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LOAD AND DEF ORMATION MEASUREMENTS OF HUMAN THIGHS AND
SEAT CUSHION FOAMS

By

AkramAli

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
of the degree of
MASTER OF SCIENCE
Department of Material Science and Mechanics

l 997

ABSTRACT
LOAD AND DEFORMATION MEASUREMENTS OF HUMAN THIGHS AND SEAT
CUSHION F OAMS

By
Akram Ali
In recent years much attention has been paid to applying physical principles and
engineering methods to the behavior of parts of the human body, considering it a structure and
a machine. This study describes the measurement of loads, deformations, and contours of
human thighs and seat cushion materials. Deformation of soft tissues and seat cushion foams
are significant factors in determining the interface contours between the seat and the back of
the thigh. The goal of this work is to represent the human interactions with seats and to provide
quantitative data to develop deformable human models. This study was conducted with related
work to develop finite element models of human and seat interactions.

A contour measurement system was built that uses wires through the seat cushion foam
samples to transfer the surface contours to a video camera with computer interface. The contour
system was used to measure deflections of people’s soft tissues with seat cushion foams of
different stiffness and thickness. While raising the foam sample and contour system into the
back of the thigh, measurements of force, and deformation of the foam and thigh were
collected.

The force versus deflection responses of the thighs did not vary significantly with different
foam stiffnesses. This work helps the automotive seat designer understand the complex

problem of contact between human soft tissues and seat cushion foams.

DEDICATION

To my parents

ACKNOWLEDGMENTS

The author like to express his sincerest gratitude to following people, for their
efforts, advice and encouragement:

Co-workers and friends for their help and support: Chris Gedraitis. Nate Radcliffe,
Barry Frost, Bruce Liu, Tanisha Gordon, F rank Mills, Melissa Sloan, Robert Boughner,
Kristy Satchell., Jamillah Gross, Jeff Basas, Damien F ron, and Theresa Atkinson.

Tammy Bush, for her friendship and time to review my work.

Clifford Beckett, for his help and idea to develop contour measurement system used
in this study.

Richard Setyabudhy, for his cooperation.

The staff in MSU Anatomy Laboratory

Dr. Norman Sauer and David Barondess, for their help and advice.

Johnson Controls, Inc., for their generous fitnding of this project and staff in Comfort
Laboratory for their help.

Dr. Ronald Averill and Dr. Roger Haut for reviewing my work and serving on my
committee.

To my graduate advisor, Dr. Robert P. Hubbard, for your friendship, guidance and
help me keeps focused these past two years. Working with you helped me to learn and
explore biomechanics. I appreciate your help and support for everything. I am proud of

this accomplishments and you made it possible for me. Thank you.

TABLE OF CONTENTS

LIST OF TABLES ........................................................................................................ vii

LIST OF FIGURES ........................................................................................................ ix
CHAPTER 1

BACKGROUND AND OBJECTIVES ............................................................................ l

1.1 Thigh Anatomy ............................................................................................... 6

1.2 Biomechanics of Soft Tissue .......................................................................... 8
CHAPTER 2

SUBJECT ANTHROPOMETRY METHODS AND RESULTS ................................... 14

2.1 Subjects Physical Characteristics ................................................................... 14

2.2 Thigh Measurement ..................................................................................... 17

2.3 F emur Measurement ................................................................................... 19

2.4 Estimate Femur Location in the Subject Thigh ............................................. 22

2.5 Thigh and Foam Contact Surface Locations ................................................. 24

2.6 Results ......................................................................................................... 27

2.7 F emur Measurement Analysis ...................................................................... 32
CHAPTER 3

LOAD-DEFORMATION MEASUREMENT METHODS ............................................ 35

3.1 Contour Measurement System ..................................................................... 37

3.2 Testing Stiffness of the Foams with and without Wires ................................. 39

3.2.1 Compression Test of Foam with Wires ........................................... 39

3.2.2 Compression Test of Foam without Wires ..................................... 40

3.3 Thigh Load-Deformations Tests .................................................................. 40

3.3.1 Thigh-Foam Interaction Test ......................................................... 40

3.3.2 Thigh-Flat, Rigid Plate Test ........................................................... 42

3.4 Uniaxial Compression Test of the Foams Samples ........................................ 43

3.4.1 Test Specimens ............................................................................ 43

3.4.1 Procedure ...................................................................................... 43
CHAPTER 4

LOAD-DEFORMATION RESULTS AND DISCUSSION ............................................ 46

4.1 Foam Mechanical Properties ........................................................................ 47

4.2 Thigh Structural Properties .......................................................................... 49

4.3 Thigh-Foam Interactions Response ............................................................... 53

4.3.1 Thigh Interaction with Difi‘erent Foam Thicknesses ........................ 56

4.3.2 Thigh Interaction with Different Foam Densities ............................. 58

4.3.3 Thigh and Foam Interactions for All Subjects ................................ 59

4.4 Normalization of Load-Deformation Responses of Thigh-Foam and Thigh-

Rigid Plate Tests ................................................................................................. 65
4.5 Thigh-Foam Interaction Contour .................................................................. 67
CHAPTER 5
CONCLUSION AND FUTURE WORK ....................................................................... 91
APPENDICES
A. Consent Form for the Non-invasive Measurement of Deformations and Loads in the
Human Thighs of Seated Postures ........................................................................... 94
B. Copyrighted Permission .......................................................................................... 95
C. Load Cell Specification ............................................................................................ 96
D. Digital Caliper Specification ..................................................................................... 97
E. Load-Deformation Responses for the Foams and Thighs ........................................... 98
REFERENCES ........................................................................................................... 158

LEST OF TABLES

Table 2.1 Subject Physical Data ..................................................................................... 15
Table 2.2 Thigh Circumferences for Small Female (5th Percentile) , Mid-Male (50th

Percentile), and Large-Male (95th Percentile) [8] ........................................................... 16
Table 2.3 Subject Test Conditions And Group Definitions .............................................. 16
Table 2.4 Subject Thigh Measurements ............................................................... 25, 26, 27

Table 2.5 Greater Trochanter (G.T.), Medial Condyle (M.C.), and Lateral Condyle (L.C.)
Coordinate Points ........................................................................................................... 28

Table 2.6 Femurs Length (L) And The Lengths Of The Sections A (La), B (Lb), And C

(Le) Measurements ......................................................................................................... 28
Table 2.7 Coordinate Points For Sections A, B, And C ............................................. 28. 29
Table 2.8 Femurs Diameters In Z And Y Directions For Sections A, B, And C ............... 29
Table 2.9 X, Y, and Z Coordinates for HP. ( Hip point) ................................................ 29
Table 2.10 Thigh Measurements to Estimate Femur Location in Subject’s Thigh ........... 30
Table 2.11 Coordinate Points of the Thigh and the Foam Contact Surface ..................... 31

Table 2.4.1 Circumference and Diameters of the Femur [l l] .......................................... 33
Table 2.12 Femurs Data Analysis ................................................................................. 34
Table 3.2 Densities, Thicknesses and Suppliers of Foams Test Samples .......................... 47
Table 4.1 First and Second Modulus of 43 kg/m3 and 52 kg/m3 Foam Densities For ASTM
and Quasi-Static Tests .................................................................................................... 49
Table 4. 2 Slope of the Fitting Lines for the First and the Second Part ............................ 53
Table 4.3 Initial Variables of the Thigh Stiffnesses .......................................................... 55

Table 4.4 Thigh Deformations Calculated form the graphs in Figures 4.34, 4.35, 4.36,
4.37 at 90 N Load with Different Foam Thicknesses and Densities, Subject No. l, Knee

angle 100° ...................................................................................................................... 56

Table 4.5 Thigh Deformations Calculated Form the graphs in Figures 4.38, 4.39, and 4.40
at 90 N Load for Different Foam Thicknesses and Densities, Subject No. 1, Knee angle
130° ............................................................................................................................... 57

Table 4.6 Thigh and Foam Deformations at 70 N Load for Thigh Interacting with Two
Different foam Densities ................................................................................................. 60

Table 4.7 Thigh and Foam Deformations at 70 N Load for Thigh Interacting with Two

Different foam Thicknesses. .......................................................................................... 62
Table 4.8 Slope of the Fitting Lines for the First and the Second Part of Thigh-Foam

Interactions .................................................................................................................... 65
Table 4.11 Slopes between Two Contact Points of Thigh-Foam Contact Area ................ 67

LIST OF FIGURES

Figure 1.1 Subject Lying on “Bed of Springs and Nails” ................................................... 2
Figure 1.2 Pressure Distribution under the Buttocks of Seated Subject with (A) Feet
Hanging Freely, and (B) Feet Supported on a Balance Pan ............................................... 2
Figure 1.3 Experimental Chair Used to Evaluate the Pressure Distribution in Seat
Cushions .......................................................................................................................... 4
Figure 1.4. A Custom Seat Contour ................................................................................. 5
Figure 1.5 Thigh Posterior Muscles Compartment ............................................................ 7
Figure 1.6 (a) Creep Function and ( b) Relaxation Function (Maxwell Model) .................. 8
Figure 1.7 Tissue Tester ................................................................................................. 10
Figure 1.8 Testing Chair was Built to Hold the Lower Leg Motionless with an Adjustable
Arm To Hold Tissue Tester ........................................................................................... 10
Figure 1.9 A Typical Load-Deformation Response of the Calf (Posterior Muscle Belly) of
the Lower Leg of Living Human Subjects [8] ................................................................. 11
Figure 1.10 Lateral-Vertical Deformation Relationship of Mid-Thigh [9] ........................ 13
Figure 1.11 Force-Displacement Relationship of Mid-Thigh [9] ...................................... 13
Figure 2.1 Thigh Measurement [1 l] ............................................................................... 17
Figure 2.2 Coordinate System Used to Measure the Femur Dimensions [11] ................. 19
Figure 2.3 Side View and Top View for the Right Thigh [11] ......................................... 22
Figure 2.4 Coordinate System of the Thigh and the Contact Surface .............................. 24
Figure 3.1 Experiment Method Set up ............................................................................ 36
Figure 3.2 Contour Measurement System ...................................................................... 38
Figure 3.3 A Wire Images Captured by the Video Camera ............................................. 38
Figure 3.4 Grid System Used on the Foam Face ............................................................ 39
Figure 3.5 Effect of Friction Force of the Wires on the Foam Stiffness ......................... 41
Figure 3.6 Stress-Strain Curve of Foams ........................................................................ 45

Figure 4.1 Hysteresis Curves Obtained From Loading and Unloading the M-4 ( 43 kg/m3
Foam Density) Foam for Two Test Trials ....................................................................... 69

Figure 4.2 Hysteresis Curves Obtained From Loading and Unloading the Thigh for Two
Test Trails ...................................................................................................................... 69

Figure 4.3 Total Deformation Versus Load Obtained from Thigh-Foam Interaction Test
for Two trials. ............................................................................................................... 70

Figure 4.4 A Typical Strain-Stress Curve for 3 Cellular Materials Obtained from Uniaxial-
Compression Foam Test ................................................................................................. 70

Figure 4.5 Typical Best-Fit Lines were Developed to Obtain Young’s Modulus for Phase
One and the Tangent Modulus for Phase Two of Compression, Quasi-Static Test. ...... 71

Figure 4.6 Typical Load- Deformation Relationship of Thigh Structure for Two Knee
Angles. .......................................................................................................................... 71

Figure 4.7 Typical Best-F it Lines Developed for Load-Deformation Response of
Thigh ............................................................................................................................. 72

Figure 4.8 Lines Fit to Load-Deformation Relationship of the Subject Thighs with
Average Thigh Stiffness ................................................................................................. 73

Figure 4.9 The Correlation Between the Circumference and Stiffnesses of Subject Thighs.
Figure 4.10 Stiffness of Subject Thighs Distributions from Their Mean ........................... 74

Figure 4.11 Comparison between the Thigh Stiffness Average of This Study (Sample No.
1) and Previous Study (Ref. No.) (Sample No. 2) .......................................................... 75

Figure 4.12 Comparison between the Average of Thigh Stiffness (Second Part) of This
Study (Sample No. 1, Knee angle 100°) and Previous Study [5] (Sample No. 2, Knee
angle 90°). .................................................................................................................... 76

Figure 4.13 Lateral-Vertical Deformation Relationship of Thigh For Knee Angles 100 .77

Figure 4.14 Total, Thigh, and Foam Deformations ......................................................... 77
Figure 4.15 Calibration Line Between the Digital Caliper and the Digitized Wire

Displacements ................................................................................................................ 78
Figure 4.16 Typical Total, Foam, and Thigh Vertical Deformations at Node 3,4 ............. 78

Figure 3. 17 Load-Deformation Relationship for the Thigh Interaction with 44 Kg/M3
Foam Density, and with Three Different Thicknesses 25 mm, 50 mm And 100 mm. Knee
Angle 100°. .................................................................................................................. 79

Figure 3. 18 Load-Deformation Relationship for the Thigh Interaction with 44 Kg/M3
Foam Density, and with Three Different Thicknesses 25 mm, 50 mm and 100 mm. Knee
Angle 130°. ................................................................................................................... 79

Figure 3. 19 Effect of The Foam Thickness on the Foam Stiffness in Thigh- Foam
Interaction Test, Foam 43 kg/m3 . .................................................................................. 80

Figure 4. 20 Load-Deformation Relationship for the Thigh Interaction with 25 mm Foam
Thickness, and with Four Different Densities 43 kg/m3, 44 kg/m3 , 49 kg/m3 and 51
kg/m3. Knee Angle 100° Subject No. 1. ......................................................................... 80

Figure 4. 21 Load-Deformation Relationship for the Thigh Interaction with 100 mm Foam
Thickness, and with Four Different Densities 43 kg/m3, 44 kg/m3 , 49 kg/m3

and 51 kg/m3. Knee Angle 100° Subject No. 1. .............................................................. 81

Figure 4. 22 Load-Deformation Relationship for the Thigh Interaction with 25 mm Foam
Thickness, and with Four Different Densities 43 kg/m3, 44 kg/m3 , 49 kg/m3

and 51 kg/m3. Knee Angle 130° Subject No. 1. .............................................................. 81

Figure 4. 23 Load-Deformation Relationship for the Thigh Interaction with 100 mm Foam
Thickness, and with Four Different Densities 43 kg/m3, 44 kg/m3 , 49 kg/m3

and 51 kg/m3. Knee Angle 130° Subject No. 1 ................................................................ 82

Figure 4.24 Effect of the Foam Densities on the Foam Stiffness in Thigh-Foam Interaction
Test, Subject No. l. ...................................................................................................... 82

Figure 4.25 Typical Total, Thigh, and Foam Vertical Deformation versus Load for Thigh
Interaction with Two Different Foam Density (43 kg/m3 and 51 kg/m3 ). 100 mm Foam
Thickness ....................................................................................................................... 83

Figure 4.26 Typical Total, Thigh, and Foam Vertical Deformation Versus Load for Thigh
Interaction with Two Different Foam Thickness (100 mm and 25 mm). and 43 kg/m3
Foam Density ................................................................................................................. 83

Figure 4.27 Typical Total, Thigh, and Foam Vertical Deformation Versus Load, Thigh
with Two Knee Angle 100° and 130° Interaction with Foam (100 mm Thickness and 51
kg/m3 Density ................................................................................................................. 84

Figure 4.28 Typical Vertical Deformation of Thigh versus Load at Node 3,3 and 3,4 ..... 84

Figure 4.29 Linearization of Typical Load-Vertical Deformation Curves for the Thigh and

Foam. Foam 43 kg/m3, Knee Angle 100°. ...................................................................... 85
Figure 4.30 Typical Load Normalization for Thigh-Foam (43 kg/m3 Foam Density)

Interaction and Thigh-Rigid Plat Tests. .......................................................................... 85
Figure 4.31 Typical Side View of Foam-Thigh Interaction Contour. .............................. 86

Figure 4.32 Average Contour of Thigh-Foam Interaction Contour, Knee angle 100° ..... 87
Figure 4.33 Average Contour of Thigh-Foam Interaction Contour, Knee angle 130o ..... 88

 

 

Figure 4.34 Standard Deviation Contour of Thigh-Foam Interaction Contour, Knee angle
100° ............................................................................................................................... 89

Figure 4.35 Standard Deviation Contour of Thigh-Foam Interaction Contour, Knee angle
130° ............................................................................................................................... 90

Figure E.1 Best-F it Lines were Developed to Obtain Young’s Modulus for Phase One
and the Tangent Modulus for Phase Two of Compression, Quasi-Static Test for 43
Kg/M3 Foam Density (Foam Without Wires). ............................................................... 98

Figure E.2 Best-F it Lines were Developed to Obtain Young’s Modulus for Phase One
and the Tangent Modulus for Phase Two of Compression, Quasi-Static Test for 43 Kg/m3
Foam Density (Foam With Wires). ............................................................................... 98

Figure E.3 Best-F it Line were Developed to obtain Young’s modulus for Phase One and
the Tangent Modulus for Phase Two of Compression, Static Test (ASTM)for 43 Kg/m3
Foam Density. ............................................................................................................... 99

Figure E.4 Best-F it Lines were Developed to Obtain Young’s Modulus for Phase One
and the Tangent Modulus for Phase Two of Compression, Quasi-Static Test For 51

Kg/m3 Foam Density (Foam Without Wires) .................................................................. 99

Figure E.5 Best-F it Lines were Developed to Obtain Young’s Modulus for Phase One
and the Tangent Modulus for Phase Two of Compression, Quasi-Static Test for 51 Kg/m3
Foam Density (Foam With Wires) ................................................................................ 100

Figure E.6 Best-Fit Lines were Developed to Obtain Young’s Modulus for Phase One
and the Tangent Modulus for Phase Two of Compression Static Test (ASTM) for 51
Kg/m3 Foam Density (Foam With Wires) ..................................................................... 100

Figure E.7 Load- Deformation Relationship of Thigh Structure for Two Knee Angles.
Subject No. 1) ............................................................................................................. 101

Figure E.8 Load- Deformation Relationship of Thigh Structure for Two Knee Angles,
Subject No. 2 ............................................................................................................... 101

Figure E.9 Load- Deformation Relationship of Thigh Structure for Two Knee Angles,
Subject No. 3 .............................................................................................................. 102

Figure E. 10 Load- Deformation Relationship of Thigh Structure For Two Knee Angles,
Subject No. 4 .............................................................................................................. 102

Figure E.11 Load- Deformation Relationship of Thigh Structure for Two Knee Angles,
Subject No. 5 .............................................................................................................. 103

Figure E.12 Load- Deformation Relationship of Thigh Structure for Two Knee Angles,
Subject No. 6 .............................................................................................................. 103

Figure E.13 Load- Deformation Relationship of Thigh Structure for Two Knee Angles,
Subject No. 7 .............................................................................................................. 104

Figure E.14 Best-Fit Lines Were Developed for Load—Deformation Curve of Thigh,
Subject No. 1 .............................................................................................................. 105

Figure E. 15 Best-Fit Lines were Developed for the Load-Deformation Curve of Thigh,
Subject No. 2 .............................................................................................................. 106

Figure E. 16 Best-Fit Lines Were Developed for the Load-Deformation Curve of Thigh,
Subject No. 3 .............................................................................................................. 107

Figure E.17 Best-Fit Lines Were Developed for the Load-Deformation Curve of Thigh.
Subject No. 4 .............................................................................................................. 108

Figure E.l8 Best-F it Lines Were Developed for the Load-Deformation Curve of the
Thigh, Subject No. 5 .................................................................................................... 109

Figure E.19 Best-Fit Lines Were Developed for the Load-Deformation Curve of Thigh.
Subject No. 6 .............................................................................................................. 1 10

Figure E.2O Best-Fit Lines Were Developed for the Load-Deformation Curve of Thigh.
Subject No. 7 .............................................................................................................. 1 1 1

Figure E.21 Load-Deformation Relationship for the Thigh Interaction with 43 Kg/m3
Foam Density, and with Two Different Thicknesses 25 mm and 100 mm, Knee angle 100°,
Subject No. 1. .............................................................................................................. l 12

Figure E.22 Load-Deformation Relationship for the Thigh Interaction with 44 Kg/m3
Foam Density, and with Three Different Thicknesses 25 mm, 50 mm and 100 mm, Knee
angle 100° Subject No.1. ............................................................................................. 112

Figure E.23 Load-Deformation Relationship for the Thigh Interaction with 49 Kg/m3
Foam Density, and with Three Different Thicknesses 25 mm, 50 mm and 100 mm, Knee
angle 100° Subject No.1 .............................................................................................. 1 13

Figure E.24 Load-Deformation Relationship for the Thigh Interaction with 51 Kg/m3
Foam Density, and with Three Different Thicknesses 25 mm, 50 mm and 100 mm, Knee
angle 100°. Subject No.1 .............................................................................................. 113

Figure E.25 Load-Deformation Relationship for the Thigh Interaction with 43 Kg/m3
Foam Density, and with Two Different Thicknesses 25 mm and 100 mm, Knee angle 130°
Subject No.1. ............................................................................................................. 1 14

Figure E.26 Load—Deformation Relationship for the Thigh Interaction with 44 Kg/m3
Foam Density, and with Three Different Thicknesses 25 mm, 50 mm and 100 mm, Knee
angle 130° Subject No.1 ............................................................................................... l 14

 

 

Figure E.27 Load-Deformation Relationship for the Thigh Interaction with 51 Kg/m3
Foam Density, and with Three Different Thicknesses 25 mm, 50 mm and 100 mm, Knee
angle 130° Subject No.1 ............................................................................................... l 15

Figure B. 28 Effect of the Foam Thickness on the Foam Stiffness in Thigh-Foam
Interaction Test, Foam 43 kg/m3 .................................................................................. 1 15

Figure E.29 Effect of the Foam Thickness on the Foam Stiffness in Thigh-Foam
Interaction Test, Foam 44 kg/m3 Subject No l ............................................................ l 16

Figure E.30 Effect of the Foam Thickness on the Foam Stiffness in Thigh- Foam
Interaction Test, Foam 49 kg/m3 Subject No. l. ........................................................... 1 16

Figure E.31 Effect of the Foam Thickness on the Foam Stiffness in Thigh- Foam
Interaction Test, Foam 51 kg/m3, Subject No. 1. .......................................................... 117

Figure E.32 Total, Thigh, and Foam Vertical Deformation versus Load, Subject No. 1
Thigh Interaction with Two Different Foam Density (43 kg/m3 and 51 kg/m3), 100 mm
Foam Thickness .......................................................................................................... 118

Figure E.33 Total, Thigh, and Foam Vertical Deformation versus Load, Subject No. 2
Thigh Interaction with Two Different Foam Density (43 kg/m3 and 51 kg/m3), 100 mm
Foam Thickness ........................................................................................................... 119

Figure E.34 Total, Thigh, and Foam Vertical Deformation versus Load, Subject No. 3
Thigh Interaction with Two Different Foam Density (43 kg/m3 and 51 kg/tn3). 100 mm
Foam Thickness ........................................................................................................... 120

Figure E.35 Total, Thigh, and Foam Vertical Deformation versus Load. Subject No. 4
Thigh Interaction with Two Different F oarn Density (43 kg/m3 and 51 kg/m3). 100 mm
Foam Thickness ........................................................................................................... 121

Figure E.36 Total, Thigh, and Foam Vertical Deformation versus Load, Subject No. 5
Thigh Interaction with Two Different Foam Density (43 kg/m3 and 51 kg/m3), 100 mm
Foam Thickness ........................................................................................................... 122

Figure E.37 Total, Thigh, and Foam Vertical Deformation versus Load, Subject No. 6
Thigh Interaction with Two Different Foam Density (43 kg/m3 and 51 kg/m3), 100 mm
Foam Thickness ........................................................................................................... 123

Figure E.38 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 7
Thigh Interaction with Two Different Foam Density (43 kg/m3 and 51 kg/m3), 100 mm
Foam Thickness ........................................................................................................... 124

Figure E.39 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 1,
Thigh Interaction with Two Different Foam Thickness (100 mm and 25 mm), and 43
kg/m3 Foam Density ..................................................................................................... 125

xiv

Figure E.40 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 2,
Thigh Interaction with Two Different Foam Thickness (100 mm and 25 mm), and 43
kg/m3 Foam Density ..................................................................................................... 125

Figure E.41 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 3,
Thigh Interaction with Two Different Foam Thickness (100 mm and 25 mm), and 43
kg/m3 Foam Density ..................................................................................................... 126

Figure E.42 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 4,
Thigh Interaction with Two Different Foam Thickness (100 mm and 25 mm), and 43
kg/m3 Foam Density ................................................................................................... 126

Figure E.43 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 5,
Thigh Interaction with Two Different Foam Thickness (100 mm and 25 mm), and 43
kg/m3 Foam Density ..................................................................................................... 127

Figure E.44 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 6.
Thigh Interaction with Two Different Foam Thickness (100 mm and 25 mm), and 43
kg/m3 Foam Density ..................................................................................................... 127

Figure E.45 Total, Thigh, and Foam Vertical Deformation Versus Load. Subject No.7,
Thigh Interaction with Two Different Foam Thickness (100 mm and 25 mm), and 43
kg/m3 Foam Density ..................................................................................................... 128

Figure E.46 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. l,
Thigh With Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and A3 kg/m3 Density) ................................................................................ 128

Figure 4.47 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 1,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 51 kg/m3 Density) ................................................................................. 129

Figure E.48 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 2,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 43 kg/m3 Density ................................................................................. 129

Figure E.49 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 2,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 51 kg/m3 Density) ................................................................................. 130

Figure E.50 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 3,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 43 kg/m3 Density ................................................................................. 130

Figure E.51 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 3,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 51 kg/m3 Density) ................................................................................. 131

XV

Figure E.52 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 4,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 43 kg/m3 Density) ................................................................................. 131

Figure E.53 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 4,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 43 kg/m3 Density) ................................................................................. 132

Figure E.54 Total, Thigh, and Foam Vertical Deformation Versus Load. Subject No. 5,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 51 kg/m3 ................................................................................................ 132

Figure E.56 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 5,
Thigh with Two Knee Angle 1000 and 130° Interaction with One Foam (100 mm
Thickness and 43 kg/m3 Density) ................................................................................. 133

Figure E.57 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 6,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 51 kg/m3 Density ................................................................................... 133

Figure E.58 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 6,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 43 kg/m3 Density) ................................................................................. 134

Figure E.59 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 7,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 43 kg/m3 Density) ................................................................................. 134

Figure E.60 Total, Thigh, and Foam Vertical Deformation Versus Load, Subject No. 7,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 51 kg/m3 Density) ................................................................................. 135

Figure E.61 Vertical Deformation of Thigh versus Load at Node 3,3 and 3,4, Subject No.
l, Foam 61, Thickness 100 mm. Knee angles 100° and 130° ........................................ 136

Figure E.62 Vertical Deformation of Thigh versus Load at Node 3,3 and 3,4, Subject
No.2, Foam 61, Thickness 100 mm. Knee angles 100° and 130° ................................... 137

Figure E63 Vertical Deformation of Thigh versus Load at Node 3,3 and 3,4, Subject
No.3, Foam 61, Thickness 100 mm. Knee angles 100° and 130° .................................... 138

Figure E64 Vertical Deformation of Thigh versus Load at Node 3,3 and 3,4, Subject
No.4, Foam 61, Thickness 100 mm. Knee angles 100° and 130° .................................... 139

Figure E.65 Vertical Deformation of Thigh versus Load at Node 3,3 and 3,4, Subject No.
5, Foam 61, Thickness 100 mm. Knee angles 100° and 130° ......................................... 140

Figure E.66 Vertical Deformation of Thigh versus Load at Node 3,3 and 3,4, Subject
No.6, Foam 61, Thickness 100 mm. Knee angles 100° and 130° .................................... 141

 

Figure E.67 Vertical Deformation of Thigh versus Load at Node 3,3 and 3,4, Subject

No.7, Foam 61, Thickness 100 mm. Knee angles 100° and 130° ................................... 142
Figure E.68 Linearization of Load-Vertical Deformation Curves for the Thigh and Foam.
Foam 43 kg/m3, Knee Angle 100°, Subject No. 1 .......................................................... 143
Figure E.69 Linearization of Load-Vertical Deformation Curves for the Thigh and Foam.
Foam 43 kg/m3, Knee Angle 100°, Subject No. 2 .......................................................... 143
Figure E.7O Linearization of Load-Vertical Deformation Curves for the Thigh and Foam.
Foam 43 kg/m3, Knee Angle 100°, Subject No. 3 ......................................................... 144
Figure E.71 Linearization of Load-Vertical Deformation Curves for the Thigh and Foam.
Foam 43 kg/m3, Knee Angle 100°, Subject No. 4 .......................................................... 144
Figure E.72 Linearization of Load-Vertical Deformation Curves for the Thigh and Foam.
Foam 43 kg/m3, Knee Angle 100°, Subject No. 5 .......................................................... 145
Figure E.73 Linearization of Load-Vertical Deformation Curves for the Thigh and Foam.
Foam 43 kg/m3, Knee Angle 100°, Subject No. 6 .......................................................... 146
Figure E.74 Linearization of Load-Vertical Deformation Curves for the Thigh and Foam.
Foam 43 leg/m3. Knee Angle 100°, Subject No. 7 .......................................................... 147
Figure E.75 Load Normalization for Thigh-Foam (43 kg/m3 Foam Density) Interaction
and Thigh-Rigid Plat Tests, Subject No. 1 .................................................................... 148
Figure E.76 Load Normalization for Thigh-Foam (43 kg/m3 Foam Density) Interaction
and Thigh—Rigid Plat Tests, Subject No. 2 .................................................................... 149
Figure E.77 Load Normalization for Thigh-Foam (43 kg/m3 Foam Density) Interaction
and Thigh-Rigid Plat Tests, Subject No. 3 .................................................................... 149
Figure E.78 Load Normalization for Thigh-Foam (43 kg/m3 Foam Density) Interaction
and Thigh-Rigid Plat Tests, Subject No. 4 .................................................................... 150
Figure E.79 Load Normalization for Thigh-Foam (43 kg/m3 Foam Density) Interaction
and Thigh-Rigid Plat Tests, Subject No. 5 .................................................................... 151
Figure E.80 Load Normalization for Thigh-Foam (A3 kg/m3 Foam Density) Interaction
and Thigh-Rigid Plat Tests, Subject No. 6 .................................................................... 152
Figure E.81 Load Normalization for Thigh-Foam (A3 kg/m3 Foam Density) Interaction
and Thigh-Rigid Plat Tests, Subject No. 7 .................................................................... 153
Figure E.82 Side View of Foam-Thigh Interaction Contour, Subject No. 1 .................. 154
Figure E.83 Side View of Foam-Thigh Interaction Contour, Subject No. 2 .................. 154
Figure E.84 Side View of Foam-Thigh Interaction Contour, Subject No. 3 .................. 155

xvii

 

Figure E.85 Side View of Foam-Thigh Interaction Contour, Subject No. 4 .................. 155

Figure E.86 Side View of Foam-Thigh Interaction Contour, Subject No. 5 .................. 156
Figure E.87 Side View of Foam-Thigh Interaction Contour. Subject No. 6 .................. 156
Figure E.88 Side View of F oam-Thigh Interaction Contour. Subject No.7 ................... 157

xviii

 

CHAPTER 1

BACKGROUND AND OBJECTIVES

“With the exception of astronauts traveling in space, human bodies are supported by
surfaces, such as floors, chairs or beds, pressing against the skin with a total force equal to
the body weight.” [1]

A knowledge of the pressure distribution and the contour of the interaction surfaces
are important in design of supporting devices which will be comfortable for normal people
to use and avoid pressure lesions in mobilized patients. However few measurement
methods of body contour and pressure distribution have been reported.

Lindan et al. [1] used a supporting surface consisting of multiple independent Springs
and nails to measure the contact pressure (Figure 1.1) by the principle of Spring
compression. He concluded that when the person was in a seated position with their back
vertical, the points of greatest pressure were under the ischial tuberosities. The position of
the legs and trunk were important factors in determining the pressure distribution under
the buttocks of a seated subject. Figure 1.2A illustrates the degree to which the maximum
pressure exerted under the ischial tuberosities in a seated subject was influenced by
allowing the feet to hang unsupported. If the feet were supported by a balance pan which
was positioned to bear some of the weight of the legs, there was a distinct transfer of
pressure from the thighs to ischial tuberosities so that the pressure on the latter was

markedly increased (Figure 1.28).

11.1111

- -*_m

 

Figure 1.1 Subject lying on “Bed of Springs and Nails”[1].

 

A B

Figure 1.2 Pressure Distribution under the Buttocks of Seated Subject with (A) Feet
Hanging Freely, and (B) Feet Supported on a Balance Pan [1].

Mooney et al. [2] designed a special chair (Figure 1.3) to evaluate seat cushions by
measuring pressure distributions. The chair, with variable back angle, variable seat angle,
and variable leg angle, could be adjusted to suit the anatomy of each subject. The tests
were performed with both legs weighted equally, as tested by scales under each foot. The
subject was tested with his hands resting on the thighs and the thighs parallel to the floor
and the seat. The pressure was measured by pneumatic cell pressure sensors developed
especially for the study. This experiment confirmed that the greatest pressures were under
the ischial tuberosities. Measurement of pressure under the ischial tuberosities effectively
measures the seat cushion’s capability to distribute these pressures. Distribution of these
pressures may mean transfer of the weight to the thigh area. This would reduce the sharp
pressure gradients between the ischial tuberostites and surrounding tissue. Other means of
transferring pressure would be to recline or lower the knees and the legs so the weight is
borne over a larger area.

The important contribution of design of seat cushions is to equalize and minimize
pressure. Pressure can be measured and can be subjectively related to comfort for the
healthy subject [2]. Several other specifications for seat design also are important, such as
heat and moisture exchange, material stability, cushion weight, and cost. There are two
characteristics of seats for seat cushion Stiffness, soft and firm. In a soft seat, the cushion
deforms to a level where pressure distribution is spread over a larger area of the body. In a
firm seat little deformation occurs, therefore the human body can be said to be more
correctly Sitting on the seat [3]. In the latter case, efforts to achieve proper pressure

distributions on the body are incorporated into the contour of the seat cushion. Custom

contours (Figure 1.4) that fit people in wheel chair are used to equalize the pressure
distribution on their body [4].

The above studies show that the thigh is important in pressure distributions between
seat cushions and people in seated postures. For this study of measurement of human thigh
and seat cushion interactions in seated postures, thigh anatomy and engineering literature

were reviewed.

 

’93-‘33" .- 34""W. ,» memm.

Figure 1.3 Experimental Chair Used to Evaluate The Pressure Distribution in Seat
Cushions [2].

 

 

.H. .

Q
.5.‘
.31 t;

«a
9..

is“

 

 

 

Figure 1.4. Custom Seat Contour [4].

1.1 THIGH ANATOMY

The thigh tissues consist of the following major anatomical components: bone,
muscle, subcutaneous fat, and Skin. The largest component of the tissues in thigh is the
muscles [5]. The muscles of the adult thigh are divided into anterior, medial, and posterior
compartments by intermuscular septa. The thigh posterior compartment interacts with seat
cushion when people Sit in chairs. The muscles of the posterior compartment of the thigh
are biceps femurs, serrritendinosus, and semirnembranosus, and they all arise from the
ischial tuberosity. The three muscles of posterior compartment are collectively known as
the hamstrings, “ham” referring to the fleshy part of the thigh and “strings” referring to the
long tendons of these muscles (Figure 1.5). The distal tendon of the biceps femoris, the
lateral hamstring, inserts on the lateral Side of the tibia, while the tendons of
serrritendinosus and semirnembranosus, the medial hamstrings, insert on the medial side of
the tibia. The three hamstrings assist the posterior hip muscles in extending the thigh and
are the chief hip flexors of the leg [6].

The muscles provide strength and protection to the skeleton by distributing load,
absorbing shock, and enabling the bones to move at the joints. Such movement usually
represents the action of muscle groups rather than of individual muscles. The muscles
perform both dynamic and static work. Dynamic work permits locomotion and the

positioning of the body segments in space. Static work maintains body posture.

 

 

 

 

r A
t
: Gluteus minimu
Piriformis
lschial
tuberosity
Biceps femoris
Semimembnnosus . .
Sciatic nerve
Semitendinosus
lliotibial
tract (cut)
rat

Figure 1.5 Thigh Posterior Muscles Compartment [6].

 

1.2 BIOMECHANICS OF SOFT TISSUE

Data describing the behavior of the bulk muscular tissue under contact loads are
necessary in mechanical analyses of thigh-seat cushion interaction. Mechanical properties
of biological tissues were described as being nonlinear, anisotropic and viscoelastic [7].
Viscoelasticity is associated with hysteresis, relaxation, and creep responses [7]. When a
body is suddenly strained and then the strain is maintained constant afterward. the
corresponding stresses induced in the body decrease with time. This phenomenon is called
stress relaxation, or relaxation. If the body is suddenly stressed and then the stress is
maintained constant afterward, the body continues to deform, and the phenomenon is
called creep. Figure 1.6 shows the creep and relaxation firnctions. If the body is subjected
to a cyclic loading, the stress-strain relationship in the loading process is usually different

from that in the unloading process, and the phenomenon is called hysteresis.

 

Defamation
Force

 

 

Force Deformatlon

 

 

 

 

 

 

 

 

 

Time Time

 

 

Figure 1.6 (a) Creep Function and (b) Relaxation Function (Maxwell Model) [7].

Some literature related to mechanical properties of bulk muscular have been
considered as references for this thesis.

In Vannah and Childress [8], they used a quasi-static test of bulk muscle tissue to
measure the load-deformation responses of the posterior muscle belly of the lower legs of
living human subjects. A high distortion indentation test was chosen to deform the tissue
in order to estimate the composite stiffness of the tissue. The stiffness of the calf was
measured using the tissue tester, an indentator with a linear variable differential
transformer (LVDT) and load cell (Figure 1.7) which measured applied displacement and
a resulting force simultaneously. A chair was built to hold the lower leg motionless (Figure
1.8) with an adjustable arm to hold the tissue tester. The indentor was defined to have
seated when the measured force exceeded 0.2 N. The indentor was threaded to a given
position; then that position was held for 60 seconds before the resulting force was
recorded.

A typical displacement-force response (Figure 1.9) was nonlinear [8]. The muscle
belly appeared to exhibit repeatable behavior without “preconditioning”. Also they noted
minimum slope of the curve at 2 mm (at low deformation) is one-fifth of that at 20 mm.
The changes in posture and muscle contraction strategies by the subject caused variations
in the shape and the stiffness of the muscle belly. In a multisubject test the stiffness at 7.0
N reaction force averaged 0.519 N/mm relaxed, and 0.769 N/mm (mild exertion).

They concluded the load-deformation response for this composite tissue always

exhibited hysteresis. The composite tissue relaxed less then 10 percent under stress in time

10

period between 5 and 1,200 seconds after indentation. Also they concluded that the

preconditioning was not necessary to observe a repeatable load-deformation response.

  
   

TEFLON-LINED LOAD CELL

Figure 1.7 Tissue Tester

 

Figure 1.8 Testing Chair was Built to Hold the Lower Leg Motionless with an
Adjustable Arm To Hold The Tissue Tester [8].

ll

 

Reaction Force (N)

N W A U! ON

1 I l l

l l T T

D

D
D

l

y—n
1
T
D

 

 

0 5 l 0 1 5 20 25 30
Applied Displacement (mm)

Figure 1.9 A Typical Load-Deformation Response of the Calf (Posterior Muscle
Belly) of the Lower Leg of Living Human Subjects [8].

Deng [9] studied the load-deformation responses of the hamstring regions of human
thighs in seated postures for ten subjects. A chair with load cells and electronic gauges
was built to support people in variety of seated postures. The chair was adjusted
according to each subject’s body Size, the subject sat in this chair with the hands dropped
to the sides of the chair. Based on the thigh circumferences, the subjects were divided into
small female, average male, and large male.

A rigid flat plate (254 X 138 mm) was pushed in a stepwise manner into the back of
subject’s thigh. The rigid flat plate could rotate about a lateral axis to align with the back
of the thigh. The load-deformation data were collected after a ten second wait after each
deformation step to allow load relaxation and to approach a quasi-static condition. The

tests were performed for different knee angles at 90, 120, 150, and 165 degree. The knee

12

angle was defined as the angle between two vectors, one from the greater trochanter of
the femur to the lateral condyle of the femur, another from the lateral condyle to the lateral
malleolus of the ankle.

The vertical deformation versus lateral deformation of the mid-thigh was plotted to
reflect the geometry change of the mid-thigh (Figure 1.10). A typical nonlinear load-
deformation relationship for a soft tissues under compression with increasing contact area
is shown in Figure 1.11. The load-deformation curves became stiffer as the knee angle
straightened and the knee angle increased. These experiments were conducts to provide
thigh geometry and structure properties for the finite element modeling. The result of
Deng’s computer model agreed with the experimental results.

As part of the development of a deformable computer model for human thigh, the
present study provided experiment data that describe foam mechanical properties, thigh
structure properties, load-deformation of the thigh-foam interaction, and the thigh
geometry for seven human subjects. Also this study focused on the variation of thigh
deformation with different foam thicknesses and densities. More Specifically the objectives
for this thesis are to measure:

1. Foam mechanical stress-stainproperties.

2. Thigh geomeny including thigh dimensions and femur location.

3. Thigh structure load-deformation responses.

4. Thigh-foam interaction responses, load-deformation relationships of the thigh

interacting with foams of different thicknesses and densities.

13

This study is a continuation of a previous study [9]. In the present study. seven
subjects were tested to measure the load-deformation response of their thighs with a rigid
plate and with foams. The testing chair of previous study [9] was modified and used for

this research.

 

 

 

 

O 10 20 30 4) 50 60 70
Vented drplmt (rum

 

 

 

 

KA9O —"— KAlm KAISJ —‘°"- M165

 

 

 

 

 

Figure 1.10 Lateral-Vertical Deformation Relationship of Mid-Thigh [9]

 

 

 

 

 

 

 

 

 

 

 

 

150 ..
125 t
It!) .
2
8 75 0
i 50
% II
0 ‘- ‘ e ; fl
0 10 20 30 4) 50 60 70
Vatleddaploeomanamu
KAOO “—i— KA120 KA150 —°-— KAlbs

 

Figure 1.11 Force-Displacement Relationship of Mid-Thigh [9].

CHAPTER 2

SUBJECT ANTHROPOMETRY METHODS AND RESULTS

2.1 PHYSICAL CHARACTERISTICS OF SUBJECTS

Different foam densities and thicknesses were used to Study the interaction between
automotive foam cushion materials and human thighs with two knee angles. Seven
volunteers were tested for the thigh and seat cushions interactions in seated posture
experiments. The standing heights of the subjects ranged from 1651 mm to 1930 mm, the
weights ranged from 489 N to 1245 N, and their ages ranged from 18 to 36 years old, and
the thigh circumferences ranged from 447 mm to 695 mm. These physical characteristics
of these subjects are summarized in Table 2.1. A written consent form was obtained from
each subject prior to testing. The consent form used in this project can be found in
Appendix 1.

Based on an anthropometric study [10], the subjects were divided into three
categories according to the circumference of their mid-thigh, small female (5th percentile),
mid-sized male (50 percentile), and large-male (95 percentile). These thigh measurements
were taken an in erect seated position. The mid-thigh circumference measurements are
summarized in Table 2.2.

An initial study was conducted with one subject; four different foam densities (51, 49,
44, 43 kg/m3) and three thicknesses (25, 50, 100 mm) were tested with different knee

angles of 100° and 130°. The purpose of this initial study was to identify the important

14

15

variables for further study. The results for the initial study will be discussed in Chapter
Four along with the results of the full scale study on all subjects.

Two different foam stiffn‘esses (51 and 43 kg/m3) and two thicknesses (25 and 100
mm) with knee angles of 100° and 130° were the test conditions for the thigh-foam
interaction tests for the remaining six subjects. In addition, a test in which the thigh was
loaded with a rigid flat plate was done for each subject. The thigh-rigid plate test was
conducted to provide load-deformation responses of the subject’s thighs for the finite
element modeling. Table 2.3 shows the test conditions that were used and the group

definition for each subject.

Table 2.1 Subject Physical Data

 

 

 

 

 

 

 

 

 

Subject No. Gender Age Height Weight Mid-Thigh
(Years) (m) (N) Circumference
(RM)
1 Male ~ 18 1930 778 520
2 Female 23 1702 600 53 1
3 Male 19 1829 689 510
4 Male 2 1 1 803 600 462
5 Male 36 l 778 9 l 2 608
6 Male 26 1930 1245 695
7 Female 29 165 l 489 447

 

 

 

 

 

 

 

16

Table 2.2 Thigh Circumferences for Small Female (5th Percentile) . Mid-Male (50th
Percentile), and Large-Male (95th Percentile) [8].

 

 

 

 

 

Subjects Minimum (mm) Mean (mm) maximum (mm)
small female 370 427 472
mid-male 442 504 550
large-male 485 559 635

 

 

 

 

 

Table 2.3 Subject Test Conditions And Group Definitions.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Subject Group Knee Rigid Foam
No. Definition angle Plate
(Degree) Thickness Densities
(turn) (kg/ 1113)
100 130 25 50 100 43 44 49 51
X X X X X X
l mid-male X X X X X X
X X X X X
X X X X X X
2 mid- X X X X X
female X X X X
X X X
3 mid—male X X X X X
X X X X
X X X
4 small X X X X X
male X X X X
X X X
5 large X X X X X
male X X X X
X X X
6 large X X X X X
male X X X X
X X X
7 small X X X X X
female X X X X
X X X

 

 

 

 

 

 

 

 

 

 

 

 

 

(A) Thigh Cross section (B) Thigh Side View

Figure 2.1 Thigh Measurement [11].

2.2 THIGH MEASUREMENT

Anthropometric measurements for the right thigh were taken with the subjects in a erect
seating posture with two knee angles of 100° and 130°. The measurements were used to draw
the thigh geometry for finite element modeling. The subject was seated in an adjustable chair
designed to support a person in variety of seated postures. The chair was adjusted according to
each subject’s body size. The backrest was adjusted to allow the subject to be seated in erect
posture. The pivots of the moveable footrest were aligned with lateral condyle to keep the
femur in the same position when the knee angle changed from 100 to 130 degrees. These
(Figure 2.1) measurements include:
1. Hip to knee length (L): the distance between the greater trochanter (G.T.) and lateral

Condyle (LC) of femur, measured by using a measuring tape and defined as thigh length

18

(L). Middle thigh section b = L/2, section a= L/4 toward hip, and section c= L/4 toward
knee were marked on the right thigh.

. Thigh circumference: measured by a measuring tape in the plane perpendicular to the long
axis of the thigh at sections a, b, and c.

. Thigh side to side width (w) and thigh anterior to posterior thickness (h): Measured by a
digital caliper placed on the plane perpendicular to the axis of the thigh at sections a, b, c.
. Thigh angle (Q): Measured by placing an angle finder on the top of the thigh in section a.
. F emur angle (7): Measured by placing an angle finder on line connected between greater
trochander (G.T.) and lateral condyle (L.C.).

. Knee angle ((1): Defined as the angle between two vectors: one from the femur greater
trochanter to the lateral condyle of femur, and another from the lateral condyle of femur to

the lateral malleolus.

These measurements are summarized in Table (2.4).

l9

 

  

 

 

Right [en-r (dorsal aspect)

 

 

 

 

 

 

Figure 2.2 The Coordinate System Used to Measure the Femur Dimensions [1 l].

2.3 FEMUR MEASUREMENT

The femur measurements were needed to estimate the dimensions and the location of
the femur relative to the external measurements of the subject’s thigh. This internal
location was also used to draw and to locate the femur in the finite element model. Six
femurs that varied in size were selected from fifty femurs stored in the MSU Gross
Anatomy laboratory. Measurements were taken (Figure 2.2) to estimate the femur
dimensions of human subject based on the femur length (L) (distance between the greater
trochanter to lateral condyle) and the femur width (distance between the lateral condyle
and medial condyle) using the following procedure:

1. Femur alignment and securing.

20

a. A center line (X axis) was drawn on flat board (360 mm X 510 mm). Figure 2.2

shows the coordinate system were used in this measurement.

b. The intercondylar groove was aligned at the origin (0,0,0) the center line (X

axis).
c. Proximal shaft was placed at section on the center line (X axis).
Tape was applied to secure the femur to the board

. The greater trochanter (G.T.), medial condyle (M.C.), and the lateral condyle
(L.C.) coordinate points were measured with respect to the origin (0,0,0) point.
These measurements are summarized in Table 2.5

. Middle femur sections b = L/2 (L = length between LC. and GT. = X01 - XLT),
section a = L/4 toward hip, and section c = L/4 toward knee were marked to
measure the length of the sections a (L,), b (L), and c (Lc ) (Figure 2.2). These
measurements summarized in Table 2.6. The X coordinates for section a, b, and c
were measured form the marks of sections a, b, and c to the origin point (0,0,0).
The Y coordinates for section a, b, and c were measured from the medial of the
femur to the center line ( X axis). The Z coordinates were measured from the top
point of the femur to board. These measurements are summarized in Table 2.7.

. The diameters of sections a, b, and c were measured in Z and Y directions because
the‘ cross section of the femur shaft is not symmetric in the Z and Y directions.
These diameters were measured by a digital caliper. These measurement were

summarized in Table 2.8.

. The X, Y, and Z coordinates for the hip point (HR) were measured by the
following procedure:

21

a. First, four points were marked around femur head. These points were projected

on the board

b. By using a circle template, a circle was selected to best fits four points.
c. The center of the circle was located and defined as hip point (HP).

6. The XHn and Yup, coordinates were measured from the center of this circle to the
origin point (0,0,0). The distance from the board to the top of femur head was
measured and defined as dimension F. The diameter in Z direction of the femur
head was measured and defined as dimension H. The, Z coordinate of the hip joint
Zap, was calculated from F and Z dimensions by the following equation

z,,,,.=F—H/2.

These measurements are summarized in Table 2.9.

22

 

 

     

l I
G - F
|
D
I“I /
‘1
, .
M.C. LC. 3 o p
Thigh Top View Thigh Side View

Figure 2.3 Top View and Side View for the Right Thigh [l l].

2.4 ESTIMATE FEMUR LOCATION IN THE SUBJECT THIGH

The femur location in the subject’s thigh was estimated by calculating the
approximate femur center line in the top and side views for subject’s thigh. To find the
femur location, three bony landmarks located on the subject thigh by palpating; lateral
condyle, medial condyle, and greater trochanter (Figure 2.3).

On the top view of the thigh, two points were marked on the thigh of each subject to
estimate the proximal femur center line. The first point was located by estimating the
distance from the greater trochanter landmark to femur center (X), calculated by the

following equations:

23

a
X:—+)
2 J

a: the skin thickness at greater trochanter landmark, measured by pinching the skin (Figure
2.3).

y: the distance from the greater trochanter to femur center, calculated by the simple linear
regression model (equation No. 1, see section 2.7).

The second point was located by estimating the mid point of the distance between lateral
condyle and medial condyle landmarks.

To estimate the femur center line in the side view, two landmarks, greater trochanter
and the lateral condyle landmarks were found by palpating on each subject’s thigh. The
femur center line was drawn on top and side view of each subject’s thigh. A digital caliper
placed on the plane perpendicular to the long axis of the thigh at sections a, b, and c
(Figure 2.3) was used to take the following measurements for each subject with two knee
angles 100 and 130 (Figure 2.3):

1. D the distance between the thigh medial side and femur center line on thigh top view.
2. E the distance between the thigh lateral side and femur center line on thigh top view.

3. F the distance between the thigh superior side and femur center line on thigh side view.
4. G the distance between the thigh inferior side and femur center line on thigh side view.
Table 2.10 shows the these measurement for each subject. The femur centers at the thigh
front view of sections a, b, and c were located by superposition the top and side views of

the thigh dimensions at sections a, b, and c (E, D, G, and F Dimensions).

24

2.5 THIGH AND FOAM CONTACT SURFACE LOCATIONS

Both the subject’s thigh and the contact surface of the foam were located in the seat
fixture space. The thigh was located by the X, Y, Z coordinates of two landmarks(the
lateral condyle and the greater trochanter of the femur). The contact surface of the foam
was located by the X, Y, Z coordinates of the contact surface corners. The lateral condyle
of the femur landmark was chosen as the origin point 0,0,0 (Figure 2.4). These

coordinates were measured by a ruler. The results can be found in Table 2.1 1

 

Figure 2.4 Coordinate System of the Thigh and the Contact Surface.

25

2.6 ANT HROPOMETRIC RESULTS

Table 2.4 shows the thigh measurements for each subject with two knee angles 100 and

 

 

 

 

 

 

 

130 degree.
Table 2.4 Subject Thigh Measurements
Subject Thigh Thigh Side Thigh Thigh Femur Hip to Group
No./ Knee Circumference to side Anterior Ang1e(¢) Angle Knee Definition
angle (1 (mm) Width (W) to (y) (L)
(m) Posterior (degree) (mm)
Thickness (degree)
0!)
(nun)
1/100° a=545 a=163 a=184 14 16 490 Mid-Male.
b=520 b=149 b=177
c=430 c=127 c=142
1/130 ° a=555 a=1 70 a=177 12 15 490 Mid-Male
b=522 b=152 b=174
c=425 c=125 c=l49
2/100 ° a=545 a=1 65 a=173 1 1 13 430 Mid-
b=510 b=145 b=170 Female
c=415 c=120 c=l37
2/130° a=562 a=168 a=167 14 15 430 Mid-
b=515 b=148 b=163 Female
c==420 c=122 c=l30
3/100° a=530 a=155 a=168 8 10 470 Mid-Male
b=495 b=145 b=156
c=395 c=l 10 c=126

 

 

 

 

 

 

 

 

 

26

Table 2.4 Continued, Subject Thigh Measurements

 

 

 

 

 

 

 

 

Subject Thigh Thigh Thigh Thigh Femur Hip to Group
No./ Knee Circumference Side to Anterior Angle(¢) Angle Knee Definition
angle a Side to (y) (L)
(mm) Width Posterior (degree)
(W) Thickness (degree) (mm)
(mm) (11)
(mm) '
3/130° a=530 a=l60 a=159 9 11 470 Mid-Male
b=498 b=l 50 b= l 53
c=385 c=112 c=120
4/100° a=489 a=146 a=151 10 13 449 Small-Male
b=468 b= l 38 b=153
c=375 c=112 c=124
4/130° a=488 a=l48 a=l47 9 13 449 Small-Male
b=475 b=140 b=149
c=382 c=109 c=124
5/100° a=625 a=180 a=206 10 15 465 Large-Male
b=608 b=162 b=210
. c=525 c=142 c=172
5/130° a=627 a=180 a=210 12 14 465 Large-Male
b=614 b=l 70 b=200
c=530 c=144 c=172
6/100° =762 a=l93 a=248 16 17 522 Large-Male
9:695 b=195 b=230
c=530 c=157 c=197

 

 

 

 

 

 

 

 

 

27

Table 2.4 Continued, Subject Thigh Measurements

 

 

 

 

 

Subject Thigh Thigh Side Thigh Anterior Thigh Femur. I-lip to Group
No./ Knee Circumference to Side to Posterior Angle(¢) Angle Knee Definition
angle (1 (mm) Width (W) Thickness (h) (y) (L)
(mm) (mm) (degree) (mm)
(degree)

6/ 130 ° a=761 a=197 a=250 18 18 522 Large-Male
b=688 b=200 =220
c=530 c=159 c=l 87

7/ 100° a=485 a=l64 a=134 12 12 420 Small-
b=447 b=1 3 I b= 146 Female
c=385 c=l 10 c=120

7/130 ° a=492 a=1 66 a=1 33 l l 12 420 Small-
b=455 b=146 b=l35 Female
c=390 c=1 12 c=120

 

 

 

 

 

 

 

 

 

28

The following tables summarized the femur measurements:

Table 2.5 Greater Trochanter (G.T.), Medial Condyle (M.C.). and Lateral C ondyle (L.C.)
Coordinate Points

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Femur No. l X(mm) Y(mm) Z(mm)
LC. 20 34 19.05
M.C. 20 34.5 25.08
GT. 400 25 22.61

Femur No. 2
LC. 17 39 23.4
M.C. 13 41.6 25.4
GT 382 21 18.7

Femur No. 3
LC. 19 32.6 24.3
M.C. 19 41 23.5
GT. 282 16 17.67

Femur No. 4
LC. 19 32 19
M.C. 19 44 23.6
GT. 370 24 16.9

Femur No. 5
LC. 20 33 22
M.C. 20 42 24.8
GT. 396 25 19

Femur No. 7
LC. 20 33 25
M.C. 20 43 23
GT. 368 25 20

Table 2.6 Femurs Length L And The Lengths Of The Sections A (L,), B (Lb), And C (Lc )
Measurements
F emur No. L (m) Lb (mm) L,& Lc (mm)
Femur 1 380 190 95
Femur 2 363 181.5 90.75
Femur 3 263 131.5 65.75
Femur 4 351 175.5 87.75
Femur 5 375 188 94
Femur 6 348 174 87

 

 

 

 

 

Table 2.7 Coordinate Points For Sections A, B, And C

 

 

 

 

 

 

 

 

Femur l X (m) Y (m) Z (mm)
a 305 20 45.19
b 210 19.5 57.32
c 115 21 58.84

 

 

 

 

29

Table 2.7 Continued, Coordinate Points For Sections A, B, And

Femur2 X m Y m Z mm
289 14 40
200 13 51
108 13 56.3

217 13 54.2
151 15 65.3
85 16 64.8

14 44.2
l4
16 55

l4
l4
l9

13
10
13

 

Table 2.8 Femurs Diameters In Z And Y Directions For Sections A, B, And C

 

 

 

 

 

 

 

 

 

 

diameter in Y directions diameter in Z directions (mm)
(mm
Femur No. ' a d c a b c

Femur 1 25.72 23.67 29.39 25.2 28.2 28.08
Femur 2 28 26 28.8 26 26.4 27.2
Femur 3 27 25.6 28 25.2 28 29.6
Femur 4 24.5 23.5 23.9 21.7 20.9 22.5
Femur 5 27.3 26.9 33.2 25 27.7 31.2
Femur 6 25.9 23.5 26 25 26.8 26.7

 

 

 

 

 

 

Table 2.9 X, Y, and Z coordinates for HP. ( Hip joint).

 

 

 

 

 

 

 

 

Femur NO- F [m] H [mmj X H.P. [mm] Y H.P.[mm Z Helm]
Femur l 58 44.18 426 39 35.91
Femur 2 52.3 41.5 401 43 31.55
Femur 3 62.7 42.8 315 49 41.3
Femur4 61.7 41.17 385 34 41.115
Femur 5 67.6 44.6 420 48 45.3
Femur 6 58.1 43.8 391 33 36.2

 

 

 

 

 

 

 

 

Table 2.10 Thigh Measurements to Estimate Femur Location in Subject’s Thigh

3O

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Knee angle 100, ‘ Knee angle 130
A B C A B C
(mm) (mm) (mm) (mm) mm) (mm)

SubjectNo. 1

D 115 89 81 112 102 77

E 40 50 47 45 52 48

F 50 58 61 48 59 65

G 126 110 73 121 106 80
Subject No. 2

D 105 89 74 108 88 73

E 46 43 40 47 46 44

F 61 62 57 53 61 57

G 108 105 69 105 86 64
Subject No. 3

D 107 90 70 113 95 79

E 41 43 37 36 45 30

F 69 70 65 66 67 68

G 98 83 62 83 76 56
Subject No. 4

D 113 80 61 102 83 53

E 41 44 46 36 43 43

F 45 62 65 46 58 62

G 89 8O 48 88 77 46
Subject No. 5

D 120 108 90 117 113 88

E 50 50 45 51 50 46

F 68 83 90 82 93 98

G 133 121 80 123 99 68
Subject No. 6

D 128 126 96 131 134 101

E 65 69 61 66 66 58

F 68 66 74 72 70 73

G 180 164 123 178 150 114
Subject No. 7

D 105 105 70 109 98 78

E 50 38 35 41 41 39

F 30 43 51 35 45 50

G 105 103 67 110 96 69

 

 

 

 

 

 

 

 

31

Table 2.11 the Coordinate Points of the Thigh and the Foam Contact Surface for the

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Subjects
subject No. 1 X (m) Y (m) Z (mm) Subject No. 4 X (m) Y (mtg) Z (mm)
LC. 0 0 0 LC. 0 0 0
G.T. 510 -10 -l40 G.T. 444 —25 -110
A 143 -25 48 A l 12 -33 75
B 357 -25 48 B 327 -33 75
C 357 242 48 C 327 237 75
D 243 242 48 D l 12 237 75
subject No. 2 subject No. 5
LC. 0 O 0 LC. 0 0 0
G.T. 475 -14 -157 G.T. 460 -21 -83
A 102 -80 90 A 120 -70 75
B 318 -80 90 B 335 -70 75
C 318 190 90 C 335 195 75
D 102 190 90 D 120 195 75
Subject No. 3 Subject No. 6
LC. 0 0 0 LC. 0 0 0
G.T. 460 -15 -120 G.T. 515 -39 -130
A 120 -84 75 A 148 -40 100
B 335 -84 75 B 362 —40 100
C 120 181 75 C 362 230 100
D 355 181 75 D 148 230 100
subject No. 7 X (m) Y (m) Z (mm)
LC. 0 0 0
G.T. 418 -12 -80
A 100 -20 75
B 315 -20 75
C 315 245 75
D 100 245 75

 

 

 

 

 

 

32

2.7 FEMUR MEASUREMENT ANALYSIS

Statistical methods [12] were used to estimate the femur dimensions for each subject.
The standard deviation (STDV) was calculated to measure the variability of the
measurement (femur dimensions) about their mean. The coefficients of determination R2
were calculated to measure the degree of linear relationship between the independent
variable: the femurs length and the femur width and the dependent variables: femur
diameters, the distance from the greater trochanter to femur center, and the X, Y, Z
coordinates for sections a, b, c, and HP, as reflected in the simple linear regression
model. The result of these analysis are given in Table 2.12.

As can be seen in Table 2.11, the mean of the femur length for this sample was 347
mm and the standard deviation was 43 mm. The linear regression model between the
femurs length and other femur dimensions (except the dimension Ym, (the distance from
the greater trochanter to femur center), and X coordinate for HP.) can not be used to
estimate the femur dimensions by knowing the femur length for the subject because the
coefficients of determination were small, possibly becouse the femurs that were chosen
belonged to people of different races or genders [13]. The coefficient of determination R2
between the femur lengths and the dimension Ym, was 0.78, so the simple linear
regression model can be used to estimate this variable.

y = 0.0741L - 3.0182 Equation (1)

y: The distance from the greater trochanter to femur center.

L: The femur length

The linear regression model between the femur dimensions and the femur width can

not be used to estimate the femur dimensions by knowing the femur width of the subject

33

because the coefficients of determination were small. However, based on statistical

analysis [13] of femur measurements of 35 females and 50 male skeletons, the diameters

of the mid-shaft femurs were estimated according to subject gender (Table 2.7.1).

Table 2.7.1. The Circumference and Diameters of the Femur [13]

 

 

 

 

 

 

 

gender Circumference Antero-posterior Transverse diameter
(mm) diameter (mm) (M)
Male 90 29 28
Female 82 27 25

 

 

34

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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CHAPTER 3

LOAD-DEFORMATION MEASUREMENT METHODS

To measure the load-deformation characteristics of the posterior sides of human thighs,
an experimental chair was used to support a person in a variety of seated postures. This
chair was first contracted and used by Deng [9] to measure the load-deformation
responses of people’s thighs by loading their thigh’s with a flat rigid plate. The movement
of this chair allowed changes in knee angle to affect the length and tension in the
hamstring muscles in the back of the thigh. This chair provided a backrest, a pelvis
support, and a movable footrest to change knee angle from 90 to 180 degrees (Figure
3.1). The knee angle was defined as the angle between two vectors: one from the greater
trochanter to the lateral condyle of femur, and another from the lateral condyle of the
femur to the lateral malleolus of the ankle. The knee angle was 180° when the leg was
completely extended. The backrest had a pivot that allowed rotation about the lateral axes
to comfortably accommodate the subjects. The chair dimensions were adjustable to
correspond to each individual’s body Size. The backrest was adjustable both vertically and
horizontally and supported the subject’s torso in the rib cage.

A plate supported the back of the pelvis, and two plates supported the right and left
buttocks. A load cell was put under each plate to measure the force under the buttocks
[7]. The load cell specifications were given in Appendix C.

A hydraulic jack with a 254 mm stroke was positioned under the right thigh. The
contour measurement system (described in the next section) was placed on the jack. A

load cell was installed between the contour measurement system and the jack. The load

35

36

cell measured the reaction force in the vertical direction under the thigh. A digital caliper
was attached between on the jack and the contour measurement system and was used to
measure the vertical displacement of the system. The digital caliper specifications were

given in Appendix C. Figure 3.1 shows the experimental method set up.

 

 

.E: '
9
.3”

i

,/ -

 

 

 

Figure 3.1 Experiment Method Set up

37

3.1 THE CONTOUR MEASUREMENT SYSTEM.

The contour measurement system (Figure 3.2) consisted of an aluminum box 213 mm x
533 mm x 165 mm, 2.56 mm diameter plastic tubes, 1.5 mm diameter steel wires, 3 clear
plastic plate to align the wires, and an alignment plate to align the tubes . Twenty four
holes were drilled on the top face of the box. The ends of plastic tubes passed inside the
box and were fixed in these holes. The other ends were fixed into the alignment plate of
the tubes. The alignment plate for the wires was clear plastic plate with 24 semicircular
slits was attached to the alignment plate of the tubes. A video camera was aligned
perpendicular to the bottom face of the box so it was facing the clear plastic plate.

F lorescent lights were behind the clear plastic plate so the image of the wires could be
captured with the video camera (Figure 3.3). A foam block with 24 holes and adjustable
spacer were on the top of the box. The holes were drilled through the foam face in a
matrix of four rows by six columns as shown in Figure 3.4. The hole numbers represent
the row and column (e.g. node 3,4 represent row 3 and column 4). Steel wires with a flat
button on one of their ends, were passed through the foam holes, tubes, alignment plate,
and into the slits of the clear plastic plate. When the foam deformed, the wires were
displaced with foam deformation. The video camera captured an image for each wire
displacement. These displacement images were digitized using a computer connected to

the camera.

38

 

 

Measurement Method

 

 

Florescent
Light

 

 

me Bunch
Steel Wire
/— Plastic tube
Weight
Balance

 

 

 

 

:/_

 

 

 

 

 

 

/ Aluminum Box
Clear Plastic Plate

( wires alignment plate)

 

 

 

 

 

: Strain Gage l l
I
CIIIDCI' I
: 3],, __-. O O 0 cl :2 I
. “ terms" -
. ] I“ Video : :
u . Camera . '
I n I
~.......IIIIIIIIIISIJIIIIZIIJ.’ ........... a

 

Figure 3.2 Contour Measurement System

 

 

 

Figure 3.3 A Wire Images Captured by the Video Camera

 

39

 

 

 

 

: : : 40mm
1 ~ - - -I ---------- I ----- I -------------

1 : I ; 45mm
2 __ _ .2 __________ I _____ I ______________ XI

1 i I , 45mm

; 3;,3 3',4 .
3 ......... e . . .e ............. —r

I ' 45mm
4 l- . .: ............................. —_x

I . 40mm

l e

   

. l , 1
20mm 45mm 45mm 45mm 45mm 45 mmZOmm

Figure 3.4 Grid System Used on the Foam Face.

3.2 TESTING STIFFNESS OF THE FOAMS WITH AND WITHOUT WIRES

To check how much the friction force between the wires and the system affected the
foam stiffness, force-compression tests were done on the foam with and with out the
wires.
3.2. 1. Compression Test of Foam With Wires

The foam was placed on the top of the contour measurement system with wires passing
through the foam, plastic tubes, and the alignment plates. A flat rigid plate (300 mm X 360
mm) was fixed on the seating fixture and horizontal to the foam testing surface (265 mm
X 215 mm). The testing surface was raised to contact the rigid plate. Contact of the
loading plate was chosen to be a small initial value of 0.22 N. The digital caliper attached
to contour measurement system recorded the vertical deformation of the foam. The testing

surface was raised in a stepwise manner typically 5 mm. The reaction forces and the

4O

deformations were recorded after 20 seconds to allow stress relaxation of the foam, which
approached a quasi-static test condition.
3.2.2. Compression Test of Foam Without Wires

The wires were taken out of the foam. The test procedure used for the foam with wires
were repeated. These tests were conducted on 43 kg/m3 and 51 kg/m3 foam densities and
100 mm. foam thickness. The data were processed and plotted using Microsoft Excel.
Figure 3.5 show the effect of the friction force on load-deformation responses of the foam
samples.
3.3 THIGH LOAD-DEFORMATION TESTS
3.3.1 Thigh-Foam Interaction Test

The chair was adjusted according to the subject’s body size. The subject sat in the
seating fixture with the feet placed firmly on the footrest plate, the head and body were in
a relaxed posture with hands dropped to the sides of the chair. All subjects wore shorts
during testing, so that clothing was not a variable. The foam was raised against the back of
the thigh and displaced in a quasi-static manner. Contact was identified when the
measurement force exceeded 0.22 N. As the foam block was pushed into the back of the
thigh, the digital caliper, that was attached to contour measurement system, recorded the
total vertical deformation of the thigh and the foam. The foam surface (265 mm x 215
mm) was raised into the thigh in displacement steps of approximately 5 mm. Each
displacement step was held for 20 to 30 seconds before the resulting force was recorded.
A rest time of 20 to 30 seconds was chosen in order to allow for short-term stress

relaxation of the thigh and foam; after this time, the forces were stable.

Load [NI
Ur
O
O

Load IN]

41

Foam 43 kg/m3

 

  

+ With wires
+ Without wires

  

 

 

 

0 10 20 3O 40 50 60 70
Displacement [mm]

Foam 51 leg/m3

 

1000
900 -~
800 «t
700 —~
600 ..
500 —~
400 ~-
300 -t
200 «~
100 ~~

L A L I
T f

0 10 20 30 4O 50 60 70
Displacement [mm]

+ With wires
+ Without wires

 

 

 

Figure 3.5 The Effect Friction Force of the Wires on the Foam Stiffness

42

The contour measurement system was displaced until the elevated foam block lifted the
subject’s leg and the foot from the footrest plate. The lateral deformation of the thigh was
recorded by placing a digital caliper across the middle section of the thigh and adjusted by
the subject. As the forces were being recorded, the foam deformation was recorded by a
video camera that captured the wire displacement images for each increment of
movement. This image was digitized by the computer.

The thigh deformation on the contact area with the foam was calculated by subtracting
the foam deformation from the total deformation. Both the subject’s thigh and the contact
surface of the foam were located in the seat fixture space (see Chapter 2.5 for more
details).

3.3.2 Thigh-Flat, Rigid Plate Test

Tests in which the thigh was loaded and deformed with a flat, rigid plate test were
needed to measure the thigh stiffness for the finite element model. The foam specimen on
top of the contour measurement system was replaced by a rigid flat plate (138 mm X 252
mm). The rigid flat pate could rotate on the lateral axis to align with the thigh posterior.
With knee angles at 100° and 130° and leg muscles relaxed, the testing surface was raised
to contact the back of the thigh. The system was defined to have contacted the thigh when
the measurement force exceeded 0.22 N. The digital caliper attached to contour
measurement system recorded the vertical deformation of the thigh. The thigh lateral
deformation was recorded by placing a digital caliper on middle section of the thigh and
adjusted for each reaction force by the subject. The testing surface was raised in stepwise

manner of 5 mm for each step. The reaction force and the deformations were recorded

43

after 20 to 30 seconds wait for short-term stress relaxation to approach a quasi-static test
condition.
3.4 UNIAXIAL COMPRESSION TEST OF FOAM SAMPLES.

In seating design most foam properties are based upon static test methods [3].
Compression tests for the foam were conducted to provide foam mechanical properties for
finite element model. The American Society for Testing and Materials [14] (ASTM D3674-
C) testing method was used to measure the force necessary to produce a 60% compressive
strain by loading over the entire area of the foams specimen. These tests were obtained by
using an Instron machine.

3.4.1 Test Specimens

The foam test specimens had parallel top and bottom surfaces and vertical sides. Their
thicknesses were 25.4 mm, 50.8 mm, and 101.6 mm. The other dimension were 382 mm
by 382 mm. These samples had different densities 41 kg/m’, 44 kg/m3, 49 kg/m3 and 51
kg/m3 that were determined from measuring their separate weights and volumes.

3.4.2 Procedure

1. Using a compression platen (flat plate 508 by 508 mm. with 6 mm holes on 20 mm
centers to allow for rapid escape of air during the test), each specimen was
precompressed twice to 60% of its original thickness at 4 mm/s.

2. Then the specimen rested for a period of 6 min.

3. An initial load of 5 N was applied to the Specimen area.

4. After the application of the initial load, the specimen was compressed 60% of the foam

thickness at 0.83 mm/s. The final position was held for 60 seconds.

44

Figure 3.6 shows the stress-strain curve obtained for all foam samples by using the ASTM
D3674-C testing method. Table 3.1 lists the different foam stiffnesses, thicknesses and
suppliers of foam samples were used in this study.

Table 3.1 Densities, Thicknesses and Suppliers of foams test samples.

 

 

 

 

 

 

 

 

 

 

 

 

Density Thickness Supplier

(kg/m3) (mm) (Company Name)
43 25.4 Atoma
43 101.6 Atoma
44 101.6 Johnson Controls, Inc.
44 50.8 Johnson Controls, Inc.
44 25.4 Johnson Controls, Inc.
49 101.6 Johnson Controls, Inc.
49 50.8 Johnson Controls, Inc.
49 25.4 Johnson Controls, Inc.
51 101.6 Johnson Controls, Inc.
51 50.8 Johnson Controls, Inc.
51 25.4 Johnson Controls, Inc.

 

 

 

 

 

45

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

14000
12000 --
3
10000 -~ , “kg/m ’
’3 3 49kg/m .
E: 8000 ‘“ 44kg/m ,4 ”/4“
§ 6000 -~ ML; if;
<72 ,
4000 4: f/
. 3
2000 —4r- 43kgm
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Strain

 

 

Figure 3.6. Stress-Strain Curve for 43 kg/m3, 44 kg/m3, 49 kg/m3, and 51 kg/m3 foams.

CHAPTER 4
THIGH AND FOAM DEFORMATIONS RESULTS AND DISCUSSION

The load and deformation responses of any material or structure depends on many
factors including the magnitude and direction of the applied load, the material that
constitutes the body, and the size and shape of the body. In discussing the thigh and the
foam interaction, it is important to distinguish between the structural and mechanical
properties. Structural properties reflect the mechanical behavior of the body as a whole,
including both material and geometric contributions of the load-deformation response
(i.e., thigh). The mechanical properties describe the intrinsic characteristics of the material
itself, and depend on its composition, molecular structure, and ultrastructure (i.e., foam,
bone tissue, or skeletal muscle tissue) [15].

Two trials of loading and unloading the thigh and the foam with a rigid plate were
conducted to check the test repeatability. Figure 4.1 shows the difference between the
load-deformation both of loading and unloading the foam 43 kg/m3 with rigid plate for two
trials were small. Figure 4.2 shows the difference between the load-deformation both of
loading and unloading the thigh with rigid plate for two test trials was small. The hysteresis
curves (Figures 4.1, 4.2) were one of the evidence of the viscolastic behavior of the soft
tissue and foam material [7]. The thigh-foam interaction test was repeated twice on the
same subject under the same test conditions (foam stiffness, thickness, and knee angle)
(Figure 4.3). The graphs of these tests (Figures 4.1,4.2, 4.3) Show that the differences
between the results of the'two trials were small, therefore the tests were considered

repeatable without having to be “preconditioned” [7,8].

46

47
4.1 FOAM MECHANICAL PROPERTIES

The load-deformation responses of the foam were measured using two methods of
uniaxial compression tests. The tests were conducted by ASTM D3674-C [l4] testing
method with an Instron machine (refer to Chapter 3 for more details). This test provided
foam mechanical properties for the finite element modeling. Tests were conducted by
quasi-static method with contour measurement system to evaluate the effect on the foam
mechanical properties of the fiiction between the wires and contour measurement system.

A typical stress-strain nonlinear relationships for cellular materials (Figure 4.4) were
obtained from the load-deformation relationship for the uniaxial compression foam tests
[16, 17, 18]. Also, the foams exhibited compressible behavior and zero Poisson (v) effect
in compression (the lateral deformation was very small compared to the large vertical
deformation, v = -latera1strain/axial strain)[16].

The stress-strain relationship (Figure 4.4) exhibited three different phases [19]. At
low strains, the foam showed a linear response followed by continuing deformation at
almost constant stress. Finally the stress increased rapidly. These three phases can be
explained in terms of the individual cells that made up the bulk foam material. When the
foam was loaded in compression, the first type of deformation which occurred is due to
bending of the cell walls (beams). This initial phase was limited to small strains (typically
5% in compression for a static test) [19]. The phase two was initiated when the critical
buckling stress for individual beams was reached. Once the beams begin to buckle,

deformation increased at almost constant load accompanied by an increase in the strain

48
energy of the deformed structure. As the cell walls continue buckling, they crush together
causing a sharp increase in stress with small change in strain [16].

A best-fit lines were developed to obtain first modulus for phase one and the second
modulus of phase two (Figures 4.5, E] to E6) of quasi—static and ASTM tests for 43
kg/m3 and 51 kg/m3 foam densities (Throughout the remainder of Chapter 4, results will be
shown with a typical Figure, like Figure 4.5, that was representative of the results from all
similar conditions, like Figure B] to E6 in Appendix B). These modulii were calculated
to find the effect of the stress relaxation between the ASTM and quasi-static tests due to
different strain rates. The strain rate of ASTM tests was 0.83 mm/s. however the quasi-
static tests were performed in stepwise manner with 20 seconds wait between each step
for stress relaxation. Also, the first and second modulii were calculated to find the effect
of friction force between the wires and the contour measurement system on the foam
material properties. Phases one and two were considered for this analysis because the
foam samples were loaded in these regions in thigh-foam interaction tests, discussed later
in this chapter.

The first and second modulus of quasi-static tests of the foam with and without wires
were considered to find the friction force effect on the foam material properties. These
tests were considered because they have the same strain rate. Therefore, the Stress
relaxation effects were eliminated as a variable between these tests. The results (Table 4.1)
showed that the fiiction forces increased the value of the first and second modulus by 9%
and 18%, respectively, for 51 kg/m3 foam density, and by 17% and 16%, respectively, for

43 kg/m3 foam density.

49
The first and the second modulus of quasi-static test and the ASTM test were
considered to find the stress relaxation effect on the foam material properties. The results
(Table 4.1) showed that the relaxation stress effect decreased the first and second modulus
for by 50% and 21% , respectively, for 51 kg/m3 foam density, and by 17% and 16%,
respectively, for 43 kg/m3 foam density.

Table 4.1 First and Second Modulus of 43 ltg/m3 and 52 kg/m3 Foam Densities For ASTM
and Quasi-Static Tests

 

 

 

 

 

 

 

Foam Density Phase I Phase 11 Foam Density Phase I Phase II
51 kg/m3 modulus modulus 43 kg/m3 modulus modulus
(Pa) (P3) (P8) (P3)
ASTM test 91832 12512 ASTM test 27007 8995
With wire 50405 12149 With wire test 26897 8983
Without wire test 45779 9916 Without wire 22385 7573
test
Friction effect % 9 18 Friction effect % 17 16
Relaxation Stress -50 -21 Relaxation -17 -16
effect % Stress effect %

 

 

 

 

 

 

 

4. 2 THIGH STRUCTURAL PROPERTIES

The load-deformation response of the thighs of seven subjects with two knees angles
100° and 130°, were measured using a thigh-rigid plate test to provided structure
properties for finite element modeling (Figures 4.6, E7 to E. 13). Both the material (a
composite of veins, skin, fat, and muscles) and geometry (thigh shape and femur location
with respect to soft tissue) of the thigh contributed to the load-deformation response. The
load-deformation (vertical deformation) relationship exhibited low stiffiless in the
beginning with large deformation at small initial load. This response became stiffer as the

thigh deformation and contact area of the thigh increased. This is a typical nonlinear load-

50
deformation relationship for a bulk soft tissue under compression with increasing in
contact area [8, 9, 20].

This behavior of the thigh tissue under compression load can be represented by
splitting the load-deformation curve into two parts (Figures 4.7, E. 14 to E.20), the first
part started from zero load to a load of approximately 30 N, the second part started at 30
N to the load of approximately 120 N. The load readings were different between the tests,
so the closest values for the 30 N and 120 N were selected for these calculations. The
second part of the curve represented the working region of the thigh stiffness when the
thigh typically interacts with a seat in seated posture. This working region of 30 N to 120
N ranged from 7% of body weight of small female (the 5th percentiles of population
weight distribution) to 12% of body weight of large male (the 95th percentiles of
population weight distribution). The working region was based on the contact pressure of
the thigh-seat interaction from the results of pressure mat for various people in the seated
postures [21]. Some automotive seat manufactures recommend that the pressure
distributed under the thigh in a typical automotive seat should range from 9% to 11% of
body weight, which was contained in the second part of the curve. Best-fit lines were
developed for each part and these lines were highly correlated to the data (R2 values of
0.93 to 0.99). The slopes of fitting lines were calculated from their equations to estimate
the thigh stiffnesses for each subject with different knee angles and to find the variance and
the average of the thigh stiffnesses for the seven subjects. Table 4.2 shows the slopes for
I the first and the second parts of each subject with two different knee angles. The average

slope (Table 4.2) for the seven subjects of the best-fit lines in the first part was 0.92 N/mm

51
for the 100° knee angle and 1.30 N/mm for the 1300 knee angle. The average slopes of
second part increased to 2.58 N/mm for the 100° knee angle and 2.96 MM for the 1300
knee angle. The thigh Stiffness increased from the first part to the second part by 65 % for
knee angle 100° and 55 % for knee angle 130°, due to the increasing in the thigh-rigid
plate contact area and to the effect of thigh soft tissue properties.

The graphs in Figures 4.6, E7 to E. 13 and the slope of the fitting lines for first and
second parts (Figures 4.7, E. 14 to E.20) showed that human thighs become stiffer as the
knee angle was straightened. The average thigh stiffness of seven subjects (Table 4.2)
(except the second part for subject number seven due to negative value which could be
due to the subject movement) increased by 14% for the first part and 11% for the second
part as the knee angle increased from 100° to 130°. These results indicated that the tension
of the hamstring muscles increased as the knee angle increased.

The variances and the average of the thigh stiffness for seven subjects with two knee
angles were calculated from the slope of the second part in deformation-load relationship
(Figure 4.8). The variances in the thigh stiffness due to the subject's characteristic (subject
thigh circumference, height, sex, age) were 0.12 (N/mm)2 for knee angle 100° and 0.59
(N/rnrn)2 for knee angle 130° with average thigh stiffnesses 2.60 N/mm and 2.96 N/mm,
respectively (Table 4.2). The correlation between the thigh stiffness and circumference
was 0.22 (Figure 4.9) for knee angle 130° and 0.024 for knee angle 100°. These results
indicated that the thigh stiffness varies from person to person and did not depend on the
their size. Also, these results indicted that, when the knee angle was 100° variation in the

thigh stiffnesses was small (5%) between the subjects and did not depended on the thigh

52
size. But when the knee increased to 130° (the tension of the hamstring muscles increased)
the variation in the thigh stiffnesses increased (from 5% to 20%) and the size dependence
increased from 0.024 to 0.22. Figure 2.10 shows the distributions of the thigh stiffnesses
from their mean for knee angle 100° and 130°.

The average of the thigh stiffness for this study was compared with a previous study
by Deng [9]. Figure 4.11 shows the data sets and the averages for both studies. Also, the
average slopes of the thigh working region (second part for the load-deformation
relationship) for both studies (Figure 4.12) were calculated to determine the variance from
their mean. The average slopes were 2.6 N/mm for this study (sample number one) and
2.3 N/mm for previous study (sample number two). The variance between these studies
was 0.045 (N/mm)2. This result indicated the variance of the averages stiffness was small
(1.8%) and the average of this study was stiffer by 12% for the previous study. This
difference between the thigh stiffnesses of these studies could be due to differences in
sample size and the knee angle.

To demonstrate the change of the thigh geometry during the tests, the lateral versus
the vertical deformations of the thigh was plotted for each subject (Figure 4.13). The
lateral-vertical deformation relationship (Figure 4.13) was nonlinear and exhibited a larger
lateral deformation with larger vertical deformation. The muscle layers slide over one
another and flow away from the area of immediate pressure, producing the lateral

deformation.

 

53

Table 4. 2 Slope of the Fitting Lines for the First and the Second Part

 

 

 

 

 

 

 

 

 

 

 

 

Knee angle 100o Knee angle 130°
Subject No. Slope Slope The Differ. Slope Slope The Differ. The Effect of the
Part Part in Thigh Part Part II in Thigh Change in knee Angle
I II Stiffness I N/mm Stiffness on thigh Stiffness
N/mm N/mm between N/mm between (Percent)
PartI&Il PartI&II
(Percent) (Percent) Part I Part II
1 0.91 2.94 69 1.32 3.03 56 13.95 2.97
2 0.60 2.02 70 1.03 2.14 52 21.29 5.61
3 1.14 2.92 66 1.90 3.05 52 22.55 14.68
4 0.86 2.73 68 1.47 2.84 48 22.34 3.87
5 0.89 2.27 61 1.09 2.56 57 8.81 11.33
6 1.21 2.83 57 1.24 4.02 69 1.06 29.60
7 0.81 2.53 71 1.04 2.19 53 8.19 -15.51*
Average 0.92 2.60 65 1.30 2.96 56 14.03 11.34
Standard 0.20 0.35 5 0.31 0.77 7 8.41 10.03
Deviation
Variance 0.04 0.12 0.10 0.59
@mrroz

 

 

 

 

 

 

 

 

 

* The negative value indicated that there were errors in the data. This could be due to the

subject movement, so this value was not considered in the average and standard deviation
calculation for the slope for the second part.

 

4.3 THIGH-FOAM INTERACTIONS RESPONSE

The load and deformation responses of the thigh-foam interactions depend on many
factors including, materials properties, geometric properties, and the magnitude and
direction of the interaction forces. There are two components of interaction forces: (1)
normal forces that are perpendicular to the thigh-foam interfaces, (2) shear forces that are
tangent to the thigh-foam interface. These shear forces result from the relative motion
between the thigh and foam. The magnitudes and distributions of the normal and shear on

the thigh-foam interaction surface determine the magnitudes and direction of the resultant

54
force components acting on the interaction surface and determine the deformation of the
sofi tissue and foam.

In the thigh-foam interaction, the thigh-foam contact surface deforms relative to the
foam support structure and the subject’s thigh soft tissues deform relative to the femur.
An assumption that the femur did not move during the test was made to calculate the thigh
deformation from the total foam deformations. Figure 4.14 shows the determination of
total, thigh, and foam deformation boundaries.

The total deformation of the thigh and foam (870,01) in the vertical direction was
measured by the displacement of the contour measurement system. The foam deformation
(8pm,) in vertical direction was calculated by digitizing the wire displacement images using
a computer software program [23]. The rigid flat plate test of the foam with wires was
used to obtain the calibration slope (Deal) by plotting the reading of the digital caliper
(Figure 3.2) (in millimeter units) with corresponding digitized wires displacement (in Pixel
units) for each displacement step (Figure 4.15). The foam deformation was calculated as
follow:

5;... (mm) =[ d’(Pire1) - d(Pi.er)] x 13..., (mm/Pixel) Equation (2)

d. : The position of the wires before the foam deformation.

d : The position of the wires after the deformation.

The vertical deformation of the thigh at the contact area with the foam was calculated by
subtracting the foam deformation from the total deformation 57m,

5mm = 5Foam + 5mg}: => 5mg}: = 8Toral - 5Foam Equation (3)

Figure 4.16 Shows the total, thigh, and the foam deformations for a typical test.

55

Two locations of foam deformation (3,3 and 3,4 nodes) were considered for the
above calculation (Figure 3.4). These nodes were chosen because they were the first
contact nodes between the thigh and the foam, and they were located at mid-thigh section.
The deformation of the mid-thigh was selected because this region deformed more
compared with other regions of the thigh.

The load-deformation responses of the thigh—foam interactions in seated postures
were studied to determine the structural behavior of thigh’s tissue with different
thicknesses and densities of foam seat cushions. The experimental data collected also
provided quantitative information for a finite element model.

A test series was conducted to estimate the variation in thigh deformation using
different variables including seven subjects, the thigh-foam contact nodes, three foam
thicknesses, four foam densities, and two knee angles. The initial number of possible
variables were 336 (Table 4.3).

Table 4.3 Initial Variables of the Thigh Stiffnesses

 

 

 

 

 

 

 

Subject Thigh-Foam Contact Foam Thicknesses Foam Densities Knee angles
Numbers Points grim) 0(g/m3 ) (degree)
7 3,3 and 3,4 Nodes 25, 50, and 100 43, 44, 49, and 51 100° and 130°

 

An initial study was conducted with subject number one to find the variation in mid-thigh
deformation with different foam thicknesses and densities. Four different foam densities
(51, 49, 44, 43 Kg/M3) and three foam thicknesses (25, 50, 100 mm) were tested with

thigh of subject number one and with two different knee angles (100°, 130°).

 

56
4.3.1 THIGH INTERACTION WITH DIFFERENT FOAM THICKNESSES.

The thigh deformations versus load for subject number one were plotted individually
for each foam density and each knee angle for all foam thicknesses (Figures 4.17. E2] to
E.27). The deformations of the mid-thigh (node 3,4) at 90 N load were calculated from
these graphs (Figure 4.17, E21 to E.27). The deformation at 90 N load was chosen based
on two facts: (1) all test ranges reached this limit of 90 N load and (2) the 90 N load
located in the working range (discussed previously in Section 4.2) of the thigh. Table 4.4
shows the mid-thigh deformation at 90 N load with all densities and thicknesses of the
foam for 1000 knee angle.

Table 4.4 Thigh Deformations at 90 N Load with Different Foam Thicknesses and
Densities, Subject No. 1, Knee angle 100°

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Thigh Deformation Thigh-different Foam
(mm) Density
Foam Thickness 51 kg/m3 49 kg/m3 44 kg/m3 43 kg/m3 Average Standard
(mm) Foam Foam Foam Foam (mm) Deviation
Density Density Density Density (mm)
100 39 46.5 43.5 42.5 42.9 3
50 42 42 45 43 1.7
25 46.5 46.5 43 42 44.5 2.3
Thigh- Average 42.5 45 43.8 42.3 43* 2*
different (mm)
Foam Standard 3.7 2.6 1 0.4 2*
Thickness Deviation
(turn)
* The means of averages and standard deviations of the thigh interacting with different foam
thicknesses and densities

The average of the thigh deformation and the standard deviation were calculated for the
thigh interacting with different foam thicknesses. Table 4.4 shows the average and the

standard deviation of the thigh deformation at 90 N for different foam thicknesses with

 

57

knee angle 100°. The means of averages and standard deviations were 43 mm and 2 mm,

respectively, of the thigh interacting with different foam thicknesses. Figure 4.17 shows

small variation in the thigh deformation of subject number one due to different foam

thickness for 43 kg/m3 foam density with knee angle 100°.

The deformations of the mid-thigh (node 3.4) with knee angle 1300 at 90 N load were

calculated from the graphs in Figures 4.18, E25 to E.27. Table 4.5 shows the mid-thigh

deformation of subject number one with 130° knee angle at 90 N load for 100 mm, 50 mm,

25 mm foam thicknesses and 51 kg/m3,44 kg/m3, and 43 kg/m3 foam densities.

Table 4.5 Thigh Deformations at 90 N Load for Different Foam Thicknesses and
Densities, Subject No. 1, Knee angle 130°

 

 

 

 

 

 

 

Thigh Deformation (mm) Thigh-different Foam Density
Foam Thickness 51 kg/m3 44 kg/m3 43 kg/m3 Average Standard
(mm) Foam Foam Foam (mm) Deviation
Densigl Density Density (mm)
100 44.5 47 44 45 1.6
50 42 48 45 4
25 46 46 44 45 1.2
Thigh- Average 44 47 44 *45 *2
different (mm)
Foam Standard *1
Thickness Deviation 2 1 0
(my

 

 

 

 

 

 

 

"' The mean of averages and standard deviations of the thigh interacting with different

foam thicknesses and densities

The average of the thigh deformation and the standard deviation were calculated for the

thigh interacting with different foam thicknesses and with knee angle 130°. Table 4.5

shows the average and the standard deviation of the thigh deformation at 90 N for

different foam thicknesses with knee angle 130°. The means of averages and standard

deviations were 45 mm and 1 mm, respectively, of the thigh interacting with different

 

58
foam thicknesses. Figure 4.18 Shows small variation in the thigh deformation of subject
number one due to different foam thickness for 44 kg/m3 foam density with knee angle
130°.

These results from subject number one indicated that the thigh deformation did not
vary significantly (3%) with different foam thicknesses. Eliminating the foam thickness as
a variable reduced the possible variable combinations of the thigh deformation from 336 to
112. In the same time, when the foam thicknesses increased (Figure 4.19), the foam
stiffnesses decreased significantly. The 100 mm and 25 mm foam thicknesses were chosen
for further analysis because they represented the softer and the stiffer foams, respectively,
for each foam density.

4.3.2 THIGH INTERACTION WITH DIFFERENT FOAM DENSITIES

The interaction effect of different foam densities with the thigh of subject number one
was determined by plotting the thigh vertical deformations versus the load for 100 mm and
25 mm foam thickness with all foam densities (Figures 4.20, 21, 22, 23). Table 4.4 shows
the thigh deformation at 90 N load with knee angle 100° for these graphs. The average and
the standard deviation were calculated to estimate the variability in the thigh deformations
for different foam densities (Table 4.4). The means of averages and standard deviations
were 43 mm and 2 mm, respectively, of the thigh interacting with different foam densities.
Figures 4.20, and 4.21 Show small variation in the thigh deformation of subject number
one due to different foam densities for 100 mm, and 25 mm foam thicknesses with knee

angle 100°.

59

The average of the thigh deformation and the standard deviation were calculated for
the thigh interacting with different foam densities and with knee angle 130°. Table 4.5
shows the average and the Standard deviation of the thigh deformation at 90 N for
different foam thicknesses with knee angle 130°. The means of averages and standard
deviations were 45 mm and 2 mm, respectively, of the thigh interacting with different
foam densities. Figures 4.22 and 4.23 Show small variation in the thigh deformation of
subject number one due to different foam densities for 100 mm, and 25 mm foam
thicknesses with knee angle 130°. Figure 4.24 displays a large difference in foam
stiffnesses due to the different in the foam densities.

These results from the first subject Showed that thigh deformation did not vary
substantially (4%) with different foam densities. Since this thesis was primarily concurred
with what was occurred in the thigh, the possible variable combinations were reduced
from 112 to 28 by eliminating the foam density.

4.3.3 THIGH AND FOAM INTERACTIONS FOR ALL SUBJECTS

Eliminating foam thickness and foam density as variables was extremely helpful in
reducing the number of tests run on subjects 2 through 7. However, two foams densities,
foam density (43 Kg/mJ) with thickness 100 mm and 25 mm and foam density (51 kg/m3)
thickness 100 mm were chosen in the further tests to evaluate the thigh behavior with
these variables. The 43 kg/m3 and 51 kg/m3 were chosen because they represent the
softest and the stiffest foams in this study.

The total, thigh, and foam load-deformation relationship (Figures 4.25, E.32 to E.38)

for the thigh interaction with two different foam densities (43 kg/m3 and 51 kg/m3) were

60
plotted for the each subject with two knee angles 100° and 130°. These graphs (Figures
4.25, E.32 to E.38) Show that the thigh deformed more than the foams and the thigh
became stiffer as the displacement and contact region increased with both foam densities.
Also, they Show there was a large difference in the foam deformation due to the different
foam densities. The difference in foam deformations increased as the displacement and
contact area increased. The deformations of the mid-thigh (node 3.4) at 70 N load were
calculated from these graphs. The deformation at 70 N load was chosen because some test
ranges did not exceed this limit of 70 N load and it was located in the working range of
the thigh. Table 4.6 shows the mid-thigh deformation with 100° and 130° knee angle at 70
N load for 100 mm foam thickness and 51 kg/m3 and 43 kg/m3 foam densities.

Table 4.6 Thigh and Foam Deformations at 70 N. Load for Thigh Interacting with
Two Different foam Densities.

 

 

 

 

 

 

 

 

 

 

 

 

Knee angle 100 Knee angle 130
Foam Deform. Thigh Deform. Foam Deform. Thigh Deform.
(mm) (turn) (turn) (turn)

Subject No. 43 5 1 43 5 1 43 5 1 43 5 l
leg/m3 kg/m3 kg/m3 kg/m3 kg/m3 lcg/m3 ltg/m3 kg/m3

1 8 2 35 37 8 2 35 36

2 12 2 45 50 10 2 45 47

3 5 1 40 40.5 7 1 35 36

4 8 1 50 51 9 1 46 47

5 4 1 51 52 5 l 43 43

6 8 2 35 37 8 1 30 31

7 4 0.5 45 47 4 4 42 43

Average 7 1 43 45 7 2 39 40

(mm)

 

 

 

 

 

 

 

 

 

 

The average foam deformations at 70 N load of the 43 kg/m3 foam was 80% larger than
51 kg/m3 foam. However, the thigh deformation did not vary significantly due to this

variable. The average of the thigh deformations at 70 N with foam 43 kg/m3 was smaller

61
by 3% than with 51 kg/m3. These results indicated that the load was distributed on the
larger contact area with softer foam and constrained the thigh so it became stiffer. Also.
these graphs (Figure 4.25) Show a large difference in the total deformations. That was
contributed by a large difference in foam deformations due to the difference in foam
densities. These results indicate a repeatable behavior of the thigh with different foam
stiffnesses.

The total, thigh, and foam load-deformation relationships (Figures 4.26, E39 to E45)
for the thigh interaction with two different foam thicknesses (100 mm and 25 mm) were
plotted for the each subject with 130° knee angle. These graphs (Figures 4.26, E39 to
E.45) Show that the thigh deformed more than the foams and the thigh became stiffer as
the displacement and contact region increased. Also, these graphs Show there was a large
difference in the foam stiffness due to the difference in foam thicknesses. This difference
increased as the displacement and the contact area increased. The deformations of the
mid-thigh (node 3,4) at 70 N load were calculated from these graphs (Figures 4.26, E39
to E.45) Table 4.7 shows the mid-thigh defamation with 1300 knee angle at 70 N load for
100 mm and 25 mm foam thicknesses and 43 kg/m3 foam density. The average of the
thigh deformations with 100 mm foam thickness was smaller by 3% than with 25 rmn
foam thickness. The average foam deformations at 70 N load of the 100 mm foam was
50% larger than the 25 mm foam. These results indicated that the load was distributed on

the larger contact area with the thick foam and constrained the thigh so it became stiffer.

62

Table 4.7 Thigh and Foam Deformations at 70 N Load for Thigh Interacting with
Two Different foam Thicknesses.

 

 

 

 

 

 

 

 

 

 

 

Subject No. Foam Deformation (mm) Thigh Deformation (mm)
100 mm 25 mm 100 mm 25 mm

1 6 3 36 38

2 8 8 42 42

3 6 3 33 33

4 5 1 49 50

5 4 1 41 43

6 l 1 4 29 31

7 4 1 42 43

Average 6 3 39 40

 

 

 

 

 

The total, thigh, and foam load-deformation relationships (Figure 4.27, E46 to £60)
for the foam interaction with thighs at two different knee angles (100° and 130°) were
plotted for the each subject with 43 kg/m3 and 51 kg/m3 foam densities. The graphs in
Figure 4.27, E46 to E.60 Show the thigh deformations decreased as the tensions of the
hamstring muscle increased as the knee angle increased from 100° to 130°, but the changes
in the foam deformations were small. This can be explained by the thigh-foam contact area
that did not change considerably due to change in knee angle. In this case, most of the
difference in total deformation was due to the difference in the thigh deformation.

Two locations of foam deformation (3,3 and 3,4 nodes) were considered for analysis
(Figure 2.8). These nodes were chosen because they were the first contact nodes between
the thigh and the foam, and they were located at mid-thigh section. To determine the
variation in thigh deformation at the contact points (3.3 and 3,4), the load versus the
vertical deformation of the thigh at these contact points (Figure 4.28, E61 to E.67) were
plotted in one graph for each subject and for each knee angle (100° and 130°). These

graphs Show that the thigh stiffnesses did not vary considerably (the difference in the thigh

 

63
deformation at 70 N was 1%) between these two contact points. This result indicated that
the femur location respect to the thigh soft tissue did not effect the deformation in these
nodes. Therefore, the possible variable combinations (variation in the thigh stiffnesses with
different foam thicknesses and densities, contact nodes, knee angle, and subject thigh
circumference) reduced from 28 to 14. The contact point 3,4 was selected for study.
These fourteen variables in the thigh deformation (the subject thigh circumference and
knee angles) were discussed earlier in this chapter (Section 4.2).

To summarize the thigh-foam interaction response, the non-linear load-deformation
curve of the thigh and foam was split into two parts. The first part was from 0 to 46 N.
This splitting point at 46 N load of thigh-foam tests (the width of testing surface was 215
mm) was equivalent to the splitting point at 30 N load of thigh-rigid plate test (the width
of testing surface was 137 mm, 30 x 215/ 138 = 46). The second part ranged from 46 to
120 N. The second part of this curve represented the working region of the thigh stiffness
when the thigh interacts with seat cushion in seated posture. The working region was
defined base on the contact pressure of the thigh-seat interaction from the results of
pressure mat for various people in the seated posture. The softest foam in this study (43
kg/m3 foam density with 100 mm thickness) was chosen for this analyses due to its large
deformations. The thigh with 100° knee angle was chosen for this analyses because it was
deformed more than with knee angle 130° (Figure 4.29). These test conditions (100° knee
angle with 43 kg/m3) presented the largest range of deformation that occurred in the thigh
and the foam in this study. A best-fit line was obtained for each part (part I and II for the

load-deformation curves of thigh and foam). The best-fit lines for the thigh (Figure 4.29,

64
15.68 to E74) were highly correlated to the data with correlation coefficients at least 0.92.
The average slopes for the seven subjects of the best-fit lines of the thigh deformation in
the first and second parts were 1.10 N/mm and 3.6 N/mm with standard deviation 0.27
N/mm and 1.17 N/mm (Table 4.8), respectively. The stiffness of the second part increased
from the first part by 69%, meaning that the thighs became stiffer as the displacement and
contact region increased. This amount of the increase in thigh stiffness is close to the
increasing in thigh stiffness when the thigh interacted with rigid plate (65%). The small
difference in the increase of thigh Stiffness in second part was probably due to load
distributed on the larger contact area in thigh-foam interaction with the large deformation
that occurred in the foam.

The average slopes of the best-fit lines of the foam deformation in the first and second
parts were 20.58 N/mm and 5.20 N/mm (Table 4.10), respectively. The stiffness of the
foam in the second part was smaller than the first part by 278%. This decrease in the
stiffness was the foam response to the increasing in the compression, shear, and tension
forces on the foam-thigh contact area. The compression force produced by the reaction
force on the foam-thigh contact area, the shear force produced by the friction force
between the thigh and foam, and the tension force produced by the differences in the foam

deformation at the contact surface.

Table 4.8 The Slope of the Fitting Lines for the First and the Second Part of Thigh-Foam

65

 

 

 

 

 

 

 

 

 

 

 

 

Interactions.
thigh foam
Subject Slope Slope The Differ. in Thigh Slope Slope The Differ. in Foam
No. Part I Part II Stiffness between Part I Part II Stiffness between
N/mm N/mm Part I & II N/mm N/mm Part I & II
%100 %100

l 1.44 4.30 66.51 12.53 4.69 -167.16

2 0.78 3.33 76.56 10.12 3.49 -189.97

3 1.29 4.35 70.34 11.14 3.73 -198.66

4 0.77 2.27 66.08 28.80 5.46 -427.47

5 1.23 2.82 56.34 33.21 5.99 -454.42

6 1.30 5.52 76.45 14.43 4.35 -231.72

7 0.92 2.61 64.75 33.85 8.66 -207.17
Average 1.10 3.60 68.71 20.58 5.20 -278.24
Standard 0.27 1.17 7.60 10.83 1.77 128.01
deviation

 

 

 

 

 

 

 

 

4.4 NORMALIZATION OF LOAD-DEFORMATION RESPONSES OF THIGH-FOAM
AND THIGH-RIGID PLATE TESTS.

The load-deformation responses of the thigh interaction with rigid plate and with the
foam were normalized to detennine the change in thigh stiffness when the thigh interacted
with the foam. To normalize the load-deformation response of the thigh, the applied loads
on the thigh were divided by the rigid plate width (138 mm) for thigh-rigid plate test and
by the width of foam specimen (215 mm) for the thigh-foam interaction test. This
normalization (Figure 4.30) of the load was based on the assumption that the load was
distributed uniformly along the thigh-foam and thigh-rigid plate contact areas.

The graphs for subjects No. 1, 2, 3, 6, and 7 (Figures E75, E76, E77, E80, E81)

of the normalization load shows that the thigh deformed slightly less when the thigh

66
interacted with foam than when it interacted with flat rigid plate. That may be because the
load in the thigh-foam interaction test was distributed on larger area due to foam
deformation. However, the graphs for subjects number 4, and 5 (Figures E78 and E79)
Show that the thigh deformed less when it interacted with the rigid plate than when the
thigh interacted with the foam. This result could be due to the load not being distributed
uniformly (due to the thigh geometry) along the contact area. Which made the assumption
of load normalization, loads were distributed unifome along the thigh-foam and thigh-
rigid plate contact areas, not valid for these two subjects (No. 4 and No. 5). Figure E85
and E86 show the foam contact areas with thigh for subjects 4 and 5 did not deform
unifome along the thigh axis. This non uniform deformation can be related to non
uniform load distribution on the thigh-foam contact area, since magnitudes and
distributions force components acting on interaction surface determine the deformation of
the soft tissue and foam. To find the degree of the variation in the deformation along
thigh-foam contour, the slopes between two contact points (points A and B, Figure 4.31)
were calculated for each subject. Figures E.82 to E.88 Show side view of thigh-foam
interaction contour for each subject with contact points A and B. Table 4.11 show the
slopes between these contact points for each subject that were calculated from Figures
E.82 to E.88. The slopes for subjects 4 and 5 were 3.7 and 2.7, respectively. Which
indicated that the deformations along the thigh-foam contact areas were not uniform for

these two subjects.

67

Table 4.11 The Slopes between Two Contact Points of Thigh-Foam Contact Area.

 

 

 

 

 

 

 

 

 

 

 

Subject No. l 2 3 4 5 6 7
Slope 1.8 1.3 0.5 3.7 2.7 0.26 1.03
(degree)

 

4.5 THIGH-FOAM INTERACTION CONTOUR

The primary functions of the automotive seat cushion are to locate the occupant in a
position where he can operate the vehicle with safely and comfort. Comfort is subjective
and can be related to the objective data such as pressure distribution and posture. There
are two extremes of seat stiffness, soft and firm. In soft seat, the cushion deforms to a
level where the pressure distribution is essentially equilibrated over a larger area of the
body. In the firm seat little deformation occurs. In the latter case, efforts to achieve proper
pressure distributions on the body are incorporated into the contour of the seat cushion.
Since all bodies are not of the same size and shape, an average contour that fits many
people's bodies is important to equilibrate the pressure over a larger area. In the seated
posture the maximum pressure occurs under the ischial tuberosities and can be minimize
by distributing the pressure on a large area of the thigh.

The foam of 43 kg/m3 density and 100 mm thickness loading the thigh for each
subject at 11% of the subject’s weight was chosen to find the average and the standard
deviation contours. The 11% subject weight load was chosen because it was in thigh
working region. This foam was chosen because it was the softest foam in this experiment
and the load the distributed on largest area compared with the others foams. Figures 4.32
and 4.33 Show the average contour of the seven subjects for knee angle 100° and 130°,

respectively. The average contour represents a best fit thigh-foam contour for all subjects

68
and can be used to distribute the pressure on the larger thigh-foam contact area. These
average contours fit the seven subjects with uniform Standard deviations contours (Figures
4.34 and 4.35). This uniform variation in foam deformation indicated that the change in

the thigh posterior contour between the subjects vary consistently due to the thigh

geometry.

69

 

 

Foam 43 kg/m3

 

700 a» + First trial
+ Second trial

Load [N]

 

 

 

 

0 20 40 60
Vertical Deforrmtion [mm]

 

 

Figure 4.1 Hysteresis Curves Obtained From Loading and Unloading the M-4 ( 43 kg/m3
Foam Density) Foam for Two Test Trials

 

Thigh-Flat Rigid Plate Test

 

160
140 “L
120 r
100 4” +First trial

+ Second trial

  
  

Load [N]
00
o

 

 

 

 

0 10 20 30 40 50 60

Vertical Deformation [mm]

 

 

 

Figure 4.2 Hysteresis Curves Obtained From Loading and Unloading the Thigh for Two
Test Trails

70

 

 

 

140 l

120 “F
100 a: +F11‘St trial
+ Second trial

 
    

80 ‘5

Load [N]

 

 

0 20 40 60 80

Vertical deforrration[mm]

 

 

Figure 4.3 Total Deformation Versus Load Obtained from Thigh-Foam Interaction Test
for Two trials.

 

 

40000 .
35000-j
30000-[ pnnez
25000-r
20000 J
15000 . Fume,
10000 4
5000 ~

     
   
 

Stress [Pa]

1'

I

 

 

0 0.2 0.4 0.6 0.8
Strain

 

 

 

Figure 4.4 Typical Strain-Stress Curve for Cellular Materials Obtained from Uniaxial-
Compression Foam Test.

71

 

Foam Without Wires, Quasi-Static Test

 

10000
9000 r” + Foam Without Wires
8000 r”
7000 *5
6000 r"

5000 r: Phasel
4000 4_ y = 22385x + 36.208
fi=0wm
3000 “ Phasell
zmo _,__ y = 7573 X+ 779.

R2 = 0.9951

_ Linear Fitting

 

 

 

 

 

 

Compression Stress (N/mz)

 

 

1000 r

 

 

 

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Strain

 

 

Figure 4.5 Typical Best-Fit Lines were Developed to Obtain Young’s Modulus for Phase
One and the Tangent Modulus for Phase Two of Compression, Quasi-Static Test.

 

 

 
  
   
    

     

  

 

 

 

Subject No.1, Thigh-Rigid Plate Test,
120
100 ._ /
—O—-Knee angle 100 /’
A 80 “I — '0 - Kneeangle 130
Z,
8 60 -
o
..l
40 -
20 -
0 . . . .
0 10 20 30 40 50 60 70
Vertical Deformation (mm)

 

 

 

Figure 4.6 Typical Load-Deformation Relationship of Thigh Structure for Two Knee
Angles.

 

72

 

 

 

    
 
 
 

Knee angle 100
120 I
Part II
100 _. y = 2.94l4x - 69.839
R2 = 0.9584
80
Z
1: 60 ..
CB
.3
40 ,_ Part1
y = 0.9109x - 2.0431
2 _
20 -. R 0.9693

  

 

 

 

0 l 0 20 30 40 50 6O 70
Vertical Deformation [mm]

 

Figure 4.7 Typical Best-Fit Lines Developed for Load-Deformation Response of Thigh.

 

73

 

 

Knee Angle 100

 

 

 

 

 

 

 

 

 

 

I40 l
f o A
I
120 7 + Sub.l - Sub. 2 0 + ’
I
, + ’ x
1 _.
00 1 0 Sub. 3 0 Sub. 4 _ /a I
2 80 i ' /
“O i 0 Sub. 5 A Sub. 691/
s g ’ -
.1 60 T “/11: l
' X Sub. 7 I Average ‘ .
40 + ‘/‘ /
A/ -./ ' x
20 -.~ 1"; " A
l /”H A
l . ’. ,.
0 ‘ ‘ t 4 1 a
0 10 20 30 40 50 60 70 80
Vertical Defamation (mm)
Knee angle 130
140
O
120 + Sub. 1
100 r- a Sub. 3
.— 80 + 0 Sub. 5
E.
'O
E 60 + X Sub. 7
40 __
20 ‘-
./ /
0 10 20 30 40 50 60 70

Vertical Defamation [mm]

 

Figure 4.8 Lines Fit to Load-Defamation Relationship of the Subject Thighs with

Average Thigh Stiffness

 

 

 

74

 

 

 

 

 

 

 

 

 

 

 

Knee angle 100
3 e
. O . O
. . 3 r: i
E e
z 2 - .
é -. R2=0.0246
g 2
5
:31 ._
.C.’
[—
1 ._ ?
0 .
400 450 500 550 600 650 700
Thigh circumference (mm)
Knee angle 130
5
r N 4 ._,._ . .
E 4 ~~
VJ 3 —o— O
5 2 —~ ° ’
0'5 2 --
TED 1 __ R2=0.2243
15
1 __t_
o i i e i
400 450 500 550 600 650 700

Thigh circumference (mm)

 

 

Figure 4.9 The Correlation Between the Circumference and Stiffnesses of Subject Thighs.

 

 

 

75

 

 

M Knee angle 100"
,Averagc Stiffness 3.03 2.93

 

    

Thigh Stiffness (Slope of the best-fit line, Part 11)
[N/mm]

Subject No.

 

 

 

Knee angle 130°

 

   

 

 

s l
g l
a. 4.02 l
4" E
g 1
a --3-.os-----"""
.3 3~
vl—i
5%
‘0-
°2
5H 2—
g
a
8
a:
a 1‘
Eb
E

0

2 4 l 5 3 5 7
SubjectNo.

 

Figure 4.10 Stiffness of Subject Thighs Distributions from Their Mean.

 

 

 

76

 

 

 

 

    
   

 

140 ‘ —— A —
120 f a SarpleNoJ 00 O
100T A SarpleNo.2 9 °
Z 307: "—AveragSarrpleNoJ a
E 60: —-'A\eragSarrpleNa.2 °
40 _-
20 ‘l
O r T _
0 10 20 30 40 50 60 70 80

Vertical Defamation [rrm]

 

Figure 4.11 Comparison between the Thigh Stiffness Average of This Study (Sample No.
1) and Previous Study (Ref. No. 9) (Sample No. 2).

 

 

 

 

 

120 .
100 +
_ 80 ~7—
E :
g 60 + +SampleNo.1,
j j y= 2.6 x -55.32
40 +
l +Sample No.2,
20 f y=2.3 x - 53.5
o 3’ +3 e 3
0 10 20 3O 40 50 6O 70

Vertical Deformation [mm]

 

 

 

Figure 4.12 Comparison between the Average of Thigh Stiffness (Second Part) of This
Study (Sample No. 1, Knee angle 100°) and Previous Study [5] (Sample No. 2, Knee
angle 90°).

 

 

77

 

 

 

 

45 :

40 a. +Sub. 7
E“ + Sub. 6
‘3
.2
‘5
E
Q—
Q)
Q
":3
.52
N
._l

0 10 20 30 40 50 60 70
Vertical Defamation [mm]

 

 

 

Figure 4.13 Lateral-Vertical Defamation Relationship of Thigh For Knee Angles 100o

 

 

 

 

 

 

Undefomed
Body

 

 

 

— — -Defamed Body

 

 

 

Figure 4.14 Total, Thigh, and Foam Defamatians

78

 

 

Caliper Reading Vs. Computer Di gi tizatian

 

  
   
  

 

 

70

:5) 60 N»—
.E’ -I- Calibration Line _
13. A .c — Linear Fitting ;
E E 50 ,
3 t ;
s 15- 4°
E Q“ 30 - Calibration Equation
,9 g y = 0.2809x
:3 5 20 " R2 = 0.9989
§ 10 ~ ‘
L“

O T f %

0 50 100 150 200 250
Foam Defamation Capture by the Computer Digitization of the Wires

Displacemnt (Pixel)

 

Figure 4.15 Calibration Line Between the Digital Caliper and the Digitized Wire
Displacements.

 

 

 

 

 

 

 

120
_,.A
u‘h.
r—n ”‘9

E.
'U

3:; —°—Foam

' Thigh

WA Total

0 IO 20 30 40 50 60

Vertical Defamation [mm]

 

Figure 4.16 Typical Total, Foam, and Thigh Vertical Defamatians at Node 3,4

 

 

79

 

 

Knee angle 100

 

200
180 r
160 “r
140 *5
120 ‘5
100 “5

 

Load [N]

 

 

 

 

0 10 20 30 40 50 60
Vertical Defirmation [nrrn]

 

 

Figure 3. l7 Load-Defamation Relationship for the Thigh Interaction with 44 Kg/M3
Foam Density, and with Three Different Thicknesses 25 mrrr, 50 mm And 100 mm. Knee

 

 

 

 

 

Angle 100°.
Knee angle 130
250
200 _- + 50 m
E 150 —— +100mm
'3 —' — 25 mm /
3 100 ~- /
/
50 7” My
0 A! 4213'.”- i l e .
0 10 20 30 40 50 60 70
Vertical Deformation [mm]

 

 

 

Figure 3. 18 Load-Defamation Relationship for the Thigh Interaction with 44 Kg/M3
Foam Density, and with Three Different Thicknesses 25 mm, 50 mm and 100 mm. Knee
Angle 130°.

80

 

43 kg/m3 Foam Density

 

l 20 Tm ~ ~-—--—---~~—~~u~ --.-_..._-_~__- ---_. ..__ z_

+25mm
+100mm

100 3*

Load [N]

 

 

0.0 5.0 10.0 15.0 20.0

 

Vertical Defonration [mm]

 

 

Figure 3. 19 Effect of The Foam Thickness on the Foam Stiffness in Thigh- Foam
Interaction Test, Foam 43 kg/m3 .

 

 

25 rrrrn Foam Thickness, Knee angle 100

 

180

 
  
 
 

—-— 44kg/rr13
+51kg/m3
+49 kg/m3
+43kg/m3

120 “5

   

Load [N]

 

 
 

l

0 10 20 30 4O 50 60

Vertical Deforrration [rrm]

 

Figure 4. 20 Load-Defamation Relationship for the Thigh Interact with 25 mm Foam
Thickness, and with Four Different Densities 43 kg/m3, 44 kg/m3 , 49 kg/m3
and 51 kg/m3. Knee Angle 100° Subject No. 1.

 

81

 

100 mm Foam Thickness, Knee angle 100

 

   
  
   

250
200 ~— +51kg/m3
+49 kg/m3
Z 150 ~~ +
1; 44kg/m3
0 —o—
—’ 100 43 kg/m3
50 ~

 

 

 

0 10 20 30 40 50 60
Vertical Deforrration [mm]

 

 

 

Figure 4. 21 Load-Defamation Relationship for the Thigh Interact with 100 mm Foam
Thickness, and with Four Different Densities 43 kg/m3, 44 kg/m3 , 49 kg/m3
and 51 kg/m3. Knee Angle 100° Subject No. 1.

 

25 mmFoam Thickness, Knee angle 130

 

140
120 «f +44kg/m3
1001‘ +51kg/m3
+43 kg/rn3

  
  
    

Load [N]

 

 

0 10 20 30 40 50 60
Vertical Defamation [rmn]

 

 

 

Figure 4. 22 Load-Defamation Relationship for the Thigh Interact with 25 mm Foam
Thickness, and with Four Different Densities 43 kg/m3, 44 kg/m3 , 49 kg/m3
and 51 kg/m3. Knee Angle 130° Subject No. 1.

82

 

100 mm Foam Thickness, Knee angle 130

 

 

 

0 20 40 60 80
Vertical Defamation [mm]

 

 

 

Figure 4. 23 Load-Defamation Relationship for the Thigh Interaction with 100 mm Foam
Thickness, and with Four Different Densities 43 kg/m3, 44 kg/m3 , 49 kg/m3
and 51 kg/m3. Knee Angle 130° Subject No. l.

 

 

250
+ 100 mm 49 kg/m3

+100 mm,51kg/m3
200 "h —e=— 100 mm, 44 kg/m3
-°—100mm,43 kg/m3

150 —~ , ,

Load [N]

100 + - .

50

l
a
O
D
O
D
D
O

 

0 5 10 15 20
Vertical Defamation [mm]

 

 

 

Figure 4.24 Effect of the Foam Densities an the Foam Stiffness in Thigh-Foam Interaction
Test, Subject No. 1.

 

83

 

 

 

   
   
     
   
  

 

 

250
Foam 43 kg/m3
200 .. —-— Thigh 43 kg/mB '.
""‘Total43kg/m3 ,.
:2: 150 «~ +Foam51kg/m3 ",1 '
g + Thigh 51 kg/m3 ' l
“I 100 ~~ "I"Tot3151kg/m3 - l
a". . .3 . l
50 "
l
l
0 . . l,
0 10 20 30 40 50 60 70

Vertical Defamation [mm]

 

 

Figure 4.25 Typical Total, Thigh, and Foam Vertical Defamation versus Load for Thigh
Interaction with Two Different Foam Density (43 kg/m3 and 51 kg/m3 ), 100 mm Foam

 

 

 

 

 

 

Thickness
Knee angle 130.
120
I
100 . .r ’
. .l
_ 80 . r '
a 60 —I— Foam, 100 mm
13; ' " Total, 100 mm
--1 40 + Thigh, 100 mm
—-- Foam 25 mm
20 - -- - Total, 25 mm
——- Thigh, 25 mm
0 r . . l i .
0 10 20 30 40 50 60 70

Vertical Defamation [mm]

 

 

L

Figure 4.26 Typical Total, Thigh, and Foam Vertical Defamation Versus Load for Thigh
Interaction with Two Different Foam Thickness (100 mm and 25 mm), and 43 kg/m3
Foam Density

84

 

 

   

250
P a
l/
/
200 4» / -
r .- -
A: -
E 150 4 7" .
'U ' ', , .
a .-
t—l 100 r“
—l— Foam knee angle 100
+ Thigh knee angle 100

 

- -I- -Total knee angle 100
Foam knee angle 130
_._.. Thigh knee angle 130

- - - ~ . Total knee @9139, ._.__l

 

0 10 20 30 . 40 . 50 60 70 8O
Vertlcal Defamation [mm]

 

 

 

Figure 4.27 Typical Total, Thigh, and Foam Vertical Defamation Versus Load, Thigh
with Two Knee Angle 100° and 130° Interaction with Foam (100 mm Thickness and 51
kg/m3 Density)

Knee angle 1(X)°

 

3 3

 

_
0+

 

 

Load [N]

 

is 3

 

 

 

0 10 ‘ 20 30 40 50 60
Vertical Defamation [nm]

Figure 4.28 Typical Vertical Defamation of Thigh versus Load at Node 3,3 and 3,4.

85

 

 

80 n

120
IOO «r
I'—
2
H 60 ‘
'0
(3
O
n—l

40 o

20 4»

 

 

  
 

  
 

  
 

  

 

Foam Part H
y =4.b97x + 35.34
R2 = 0.9781

   

 

 

  

 

 

 

 

  

   

 

 

 

 

 

 

 

 

 

 

Thigh Part II
Foam Pan I y =4.2963x - 89.879
y = l2.538x + 6.88l8 R2 = 0973.;
R2 =0.929
Thigh Part I
y -- 1.449ix - 3.5867
R2 =O.95|6
5 IO 15 20 25 3o 35 4o 45
Vertical Deformation [m]

 

Figure 4.29 Linearization of Typical Load-Vertical Deformation Curves for the Thigh and

Foam. Foam 43 kg/m3, Knee Angle 100°.

 

 

Load [N/mm]

0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1

 

 

 
  
  

+ Thigh-Foam
+ Thigh-Rigid Plate

 

 

 

10 20 3O 40 50 60
Vertical Deformation [mm]

 

 

Figure 4.30 Typical Load Normalization for Thigh-Foam (43 kg/m3 Foam Density)

Interaction and Thigh-Rigid Plat Tests.

 

86

 

 

Foam-Thigh Interaction Contour
Side View . sub. 7
Reaction Force 72N

 

 

 

 

 

 

 

 

O-
//
B_5 ..
\
E A
E -lOi
_____> Toward the Knee
-15< — >
-20 l
SI 32 S3 S4

 

Figure 4.31 Typical Side View of Foam-Thigh Interaction Contour.

 

87

 

 

 

 

 

Thigh-foam Inercation Contour, Front View
0
-5 <
-10
mm

-] 5 ‘R

'20 Toward the medial

-25 S]

6 5 4 3 2 l

 

 

 

 

 

 

S 1 S2 S3 S4

 

 

 

Thigh-foam Interaction 3D Contour,

   

1 2 3

V\ 4
Toward the \
medial

 

 

 

Figure 4.32 Average Contour of Thigh-Foam Interaction Contour, Knee angle 100°

88

 

Thigh-foam Interaction Contour,Front
View

 

 

4———
'20 Toward the medial
-25 ~ 81

 

 

 

 

 

 

Thigh-foam Interaction Contour, Side
View

——>
'20 Toward the knee
-25 , .

S1 82 S3 S4

 

 

 

 

 

 

Thigh-foam Interaction 3D Contour

 

5
Toward the \ 6 the knee
medial

 

 

 

Figure 4.33 Average Contour of Thigh-Foam Interaction Contour, Knee angle 130°

 

 

89

 

Thigh-foam Interaction Contour, Front View

 

0

 

 

 

 

- 15 <
<—
-20‘ Toward the media]
-15 . - . SI
1 2 3 4 5 6

 

 

 

 

 

 

-20+ Toward the knee

 

 

 

$1 $2 83 S4

 

 

 

 

Thigh-foam Interaction 3D Contour

 
 

S4

S3
sz/‘
2 3 4 3‘ Toward the

\ 5 6 knee

Toward the medial

 

 

 

Figure 4.34 Standard Deviation Contour of Thigh-Foam Interaction Contour, Knee
angle 100°

 

9O

 

Thigh-foam Interaction Contour, Front View

 

 

 

0 1

-5 V
-101
-15.
4.____..
-20‘ .
Toward the medial
l

-25 ‘ SI

1 2 3 4 5 6

 

 

 

 

Thigh-foam Interaction Contour, Side

 

 

 

 

 

View

0

-5
-10 *

mm -15 , ’
Toward the knee
-20‘
-25 ~ 1
SI 82 S3 S4

 

 

Thigh-foam Interaction 3D Contour

Toward the
- knee

 

Toward the medial

 

 

 

Figure 4.35 Standard Deviation Contour of Thigh-Foam Interaction Contour, Knee
angle 130°

CHAPTER 5

CONCLUSIONS AND FUTURE WORK

The objectives of this study were to measure load-deformations responses of the
human thigh with difi‘erent foam thicknesses and densities and to provided thigh geometry,
thigh structural properties and foam mechanical properties for finite element modeling.

Thigh dimensions for three sections were measured for seven subjects. F emur bone
geometry was estimated from statistical analyses of six femurs measurements. The location
of the femur in each subject’s right thigh was estimated by locating three landmarks:
lateral condyle, medial condyle, and greater trochanter.

The load-deformation responses of the thighs of seven subjects with two knees angles
100° and 130° were measured using a thigh-rigid plate test to provide structure properties
for finite element modeling. The initial load to deformation ratio was very small. As the
load increased, the sofi tissues of the thigh at the contact region were deformed vertically
and laterally, and the contact area increased greatly. As a result, the load to deformation
ratio increased. This is a typical nonlinear load-deformation response for soft tissues under
compression with increasing in contact area.

The behavior of the thigh tissue under compression load was represented by splitting
the load-deformation curve into two linear parts. The second part of the curves represents
the working region of the thigh stiffness when the thigh typically interacts with the seat in
seated postures. Lines were fit by regression equations to estimate the thigh stiffness for

each subject with different knee angles and to find the variance and the average of the

91

 

92

thigh stiffness for the seven subjects. Also the fitting lines for the second part could be
used to linerearize the thigh structural behavior.

A typical nonlinear stress-strain relationship for cellular materials was obtained from
the load-deformation for the uniaxial compression test of foam samples. The stress-strain
relationship exhibited three different phases. At low strains, the foam showed a linear
response followed by continuing deformation at almost constant stress. Finally the stress
increased rapidly. The foam exhibited highly compressible behavior and zero Poisson (v)
effect in compression.

The thigh-foam interaction contour was accomplished by transferring the deformed
shape of the foam surface to video images using wires through the foam. Deformation of
the mid-thigh was selected for studying the large deformation of the soft-tissues with
different foam thicknesses and densities. As the thighs and foams were loaded, the
deformation of the thigh was relatively large and the initial stiffness was low. The initial
deformations in the foam were smaller with stiffness that was greater than the thigh. As
loading increased, the stiffness of the thigh increased and the stiffness of the foam
decreased. The thigh deformations did not vary significantly with different foam
thicknesses and densities but did vary with different knee angles. That means that changing
the posture affects the thigh deformation more than the foam stiffnesses.

This study provided quantitative data to develop a deformable model and useful

information for thigh-foam interaction behavior that can be used in seat cushion design.

 

93

Work is ongoing to measure the contour of the thighs, buttocks, and the backs for
different people in different seated postures with different foam stiffnesses. The
recommendations for future work are:

l. Relate thigh deformation to subjectively feel of comfort .

2. Study time-deformation responses of the thigh and buttock. This can be used to
evaluate the change in the thigh-foam contour in time with seated posture.

3. Measure the corresponding load for each wire displacement to proved the finite
element model load-displacement data for each node (wire). This can be measured by
using pressure mat on the seat cushion.

4. Measure the three-dimensional contours of thighs and buttocks before and after
deformation by using a combination of contour measurement system and motion
analysis system. This will provide useful information to study the change in human

contours due to the deformation in the soft tissue in seated posture.

APPENDICES

APPENDIX A

CONSENT FORM FOR THE NON-INVASIVE MEASUREMENT OF
DEF ORMATIONS AND LOADS IN THE HUMAN THIGHS OF SEATED
POSTURES

INFORMED CONSENT STATEMENT

I. . consent to serve to an experimental subject in the research project. “Non-
invasive measurement of deformation and load in the thighs and buttock of sitting pe0ple.” The purpose
of this research project is to study the deformation characteristics of the back of human thighs and
buttocks as they are loaded by a deformable cushion like foam that is typical for seats in automobile seats
or office chairs. You will be seated in a special chair that supports your back, pelvis. and feet. and a
surface will be raised into contact with the back of your thigh for about half the area between your
buttocks and knee. This surface will be either a flat plate or a padded cushion. This surface will be raised
until the weight of your leg is fully supported. There is no restraint of your leg to upward movement and
the limit of the load on the back of your thigh will be the weight of your leg. This procedure will be
repeated with your foot supported in different positions to obtain information at various angles of your
knee. The results from these measurements will be compared to the results from a theoretical computer
model and used to improve the understanding of the interactions between people’s bodies and the seats
that support them.

I have been thoroughly informed of the purpose and procedures of this study in which I will participate.

I have been advised that all work will be conducted under the supervision of individuals who are
experienced with measuring loads and deformations in the thighs of human subjects.

I have been given an opportunity to request that the experimenter be of my same gender.

I understand that the tests are non-invasive and that it will take twenty minutes to take anthropometric
measurements, next it will take one hour to collect seated measurements of thigh deformation.

I have been assured that my participation remains confidential, and published experimental results will
not reveal my identity.

My consent to serve as subject is given freely and without coercion.

Further, I understand that I may withdraw from this experiment at any time and reason of my choice.

 

 

 

 

 

 

 

SUBJECT SIGNATURE DATE

TYPED OR PRINTED NAME ADDRESS
PHONE NUMBER

WITNESS DATE

 

TYPED OR PRINTED WITNESS’ NAME
If you have any questions, contact Prof. Robert Hubbard at 517-353-5013 or hubbard@msm.msu.edu

94

 

APPENDIX B
COPYRIGHT PERMISSION

- {US} , ..
l2)" 1944 Q4. 1
37:2

:1-

lQAKU-SHOIN MEDICAL PUBLlSHERS. INC.

ONE MADISON AVENUE. new YORK, NY 10010
(212) 779-0123 Fax (212) 7790322

September 2 7, 1996

Mr Akratn Ali

Biomechanics Department

E Fee Hall, Rm A-439

Michigan State University

College of Osreopathic Medicine

Department of Osteopathic Manipulative Medicine
East Lansing, Micigan 48824-1316

Dear Mr Ali

Please note that the request to reproduce the material quoted on the attached form(s) is
granted

Also be advised that the credit line should read "Courtesy of Johannes W. Rohen,
Drmed , Chihiro Yokochi, MD, in collaboration with ECB. Hall-Craggs from the book
COLOR ATLAS OF ANATOMY A PlIOTOGRAPI-IIC STUDY OF THE HUMAN
BODY, SECOND EDITION, Igaku-Shoin Medical Publishers, New York. NY, 1988 "

Please don't hesitate to contact me ifyou have any questions or ifl can be of any fitrther
assistance.

Sincerely,
‘. . \ ~__‘(__
, r t J _- 7Q
L _. -— - __ \_. __,o’ \
Alina Cttsati

Editorial Assistant

Enclosure

95

APPENDIX C

LOAD CELL SPECIFICATION

 

 

Load Static Error Non-linearity
Range Band (+l-%) F.$.)' (°/. F.s.)"
Model 45 ................. 200; 500; 1.000; .05 05
2 GOO-10.000 0 .05
25 000; 50.000; .05 .05
100.000 .07 .05
Model 47 ................. 200; 500; 1.000; 2.000 .02 .02
5.000; 10.000 .03 .03
25.000; 50.000 .04 .03
100.000 .06 05

Output (std) .................................
Fatigue lite .. .....

2mv/v
10°, Fully reversed
meI Io/o

  

 

 

Resolution: ........................ Iriirntte
Temperature. Operating ............... -65° to 200° F
Temperature. Compensated ........ 0° to 150° F

Temperature Eitect
- Zero (max) ..............................
- Span (max) ................

.10°/o F.S./100° F
.15% F.S./100° F

  

 

Strain Gage Type ............... Bonded tori
Excitation (calibration) .....
Excitation (acceptable) .. .....
insulation Resistance .....

 
 
 
 
  

10VDC
Up to 15VDC or VAC
5000 megaohms @ 50VDC

 

Bridge Resistance .............. 350 ohms

Shunt Calibration Data ..... Included

Wiring Code .................................. See Below

Electrical Termination (std) .......... PCOZA~10~6P (cable optional
With 1/4 NPT

condutt connection)
Mating Connector (not incl.) PC06A-10-68
Static Overload Capacity ............. 200%

Deflection—Full Scale ..................
Material

17-4 'PH stainless steel

 

Outputs Available .........................

96

+/- 5VDC, 4-20 mA

APPENDIX D

DIGITAL CALIPER SPECIFICATION

 

Mitutoyo and Starrett
Electronic Depth Gauges

Sliding scale and LCD provide quick,
easy-to-read depth measurements of
holes, slots. and recesses.

Display features inch/mm conversion,
zero setting. and SPC output. A knurled
screw locks gauge on the hardened stain-
less steel bar. Battery and fitted case are in-
cluded.

srit‘fii‘aé‘t‘i 74s sen’res
0-6"/150mm ........ 745245....10001~ (0.025mm)...85945A66... 236.60

7" Extension ....... 745E-7 ..................................... 85945A67... 26.25
12" Extension ..... 745E-12 ................................... 85945A68... 44.80
SPC Cable .......... 22650 ....................................... 8602A66 ..... 29.95
Replacement Battery (requires 2) .................. .....21105A169 1.14

97

 

 

 

'.'~‘ £4;’__.. .. 2

APPENDIX E

LOAD-DEFORMATION RESPONSES FOR THE F OAMS AND THE THIGHS

 

Foam Without “fires, Quasi-Static Test

 

10000
9000 “r + Foam Without Wires
8000 4*
7000 *E
6000 7*

5000 “r Phase I
4000 «P y = 22385x + 36.208

#=0%m
3000 + Phase II t

—" Linear Fitting

 

 

 

 

 

L-

2000 +_ y=7573x+779.|
R2=0.9951 j

Compression Stress (N/mz)

 

1000 r

 

 

 

O 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Strain

 

 

 

Figure B] Best-Fit Lines were Developed to Obtain Young’s Modulus for Phase One
and the Tangent Modulus for Phase Two of Compression, Quasi—Static Test for 43
Kg/M3 Foam Density ( Foam Without Wires).

 

 

 

 

 

 

 

 

 

 

 

 

Foam With Wires, Quasi-Static Test
IOOOO
9000 .. + With wires
”A 80“) ‘5 —Linear Fitting
E ._
Z 7000
a 60m -tl-
5 5000 4» Phase 1
,5 y= 26897x + 32.073 :
g 4000 R2 = 0.9931 E
=- _ :1
g 3000 l , Phase 11
U 2000 a» y = 8983x + 980.82
1000 ,5 R‘ = 0.9906
O Y I
0 O l 0 2 O 3 0.4 O 5 0 6 O 7
Strain

 

 

 

Figure E.2 Best-Fit Lines were Developed to Obtain Young’s Modulus for Phase One
and the Tangent Modulus for Phase Two of Compression, Quasi-Static Test for 43 Kg/m3
Foam Density (Foam With Wires).

98

 

 

99

 

 

 

 

 

 

 

 

 

 

 

 

Foam Without Wires, Static Test
10000

of; 9000 ‘* —M-4Instron

2 8000 «I Linear fitting

5 7000 7*

g 6000 “r

:3 5000 -_ - Phasel

.g 4000 4— "$923,392?”

9.03 3000 .1.— ' l Phase II . }
c. =8995+1393.9' .
g 2000 T [I R2=0.9922 ; l
U 1000 7

0 . i
O 0.1 0.2 0.3 0.4 0.5 0.6
Stan

 

 

 

Figure E.3 Best-F it Line were Developed to obtain Young’s modulus for Phase One and
the Tangent Modulus for Phase Two of Compression, Static Test (ASTM)for 43 Kg/m3
Foam Density.

 

 

  
 
  
 
 
 
   
  

 

 

 

 

 

 

 

 

 

 

 

Foam Without Wires, Quasi-Static Test
18000
NA16OOO —» --a— Without Wires
\ 14000 " —LinaerFitting
a 12000 I" Phasel
‘1’ . =45779x- 111.99
531 10000 y R2=0.9905
g 8000 «-
‘E Phasel]
3 6000 T y=99]6.lx+4950
g. 4000 . R2=0.98i7
5 2000 a
0 T + . . . t
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Stan

 

 

 

Figure 13.4 Best-Fit Lines were Developed to Obtain Young’s Modulus for Phase One
and the Tangent Modulus for Phase Two of Compression, Quasi-Static Test For 51
Kg/m3 Foam Density (Foam Without Wires).

 

—: .1---I —‘——— '

100

 

Foam With Wires, Quasi-Static Test

 

18000
6000 b —O—With wires
1 —-Linear Fitting /I'I

14000 ~ .'

I

 

12000 7* Phasel , I

10000 ""
8000 ~~
6000 7"

 

 

 

 

 
    

Phas ll
y -12149x + 4792.4
F12 = 0.9849

Compression Stress (N/mz)
A
O
O
O

 

 

2000 7*

 

 

 

 

L - A
, r

0 0.1 0.2 0 0.4 0.5 0.6 0.7

.3 ,
Samn

 

 

 

Figure E.5 Best-Fit Lines were Developed to Obtain Young’s Modulus for Phase One
and the Tangent Modulus for Phase Two of Compression, Quasi-Static Test for 51 Kg/m3

 

 

 

 

 

 

 

 

 

 

 

 

 

Foam Density ( Foam With Wires).
Foam Static Test
42000
39000 4+
NA 36000 4» Instron test
E 33000 ~r ——1.'nw Fitting
\
a 30000 a
to 27000 <~
8 24000 ..
I:
U) 21“» ** Phase I
S 18000 t y =91832x- 81.073
a; 15000 + R2 = 0.9956
«a 12000 «~ ' q
E m " Phade [I
o 6000 «» y=12512x+5057.8
U 3000 i» R’ =0.987
0 e 4‘ " i Jfi r
o 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Stan

 

 

 

Figure E.6 Best-Fit Lines were Developed to Obtain Young’s Modulus for Phase One
and the Tangent Modulus for Phase Two of Compression Static Test (ASTM) for 51
Kg/m3 Foam Density ( Foam With Wires).

 

101

 

Subject No.1, Thigh-Rigid Plate Test,

 

 
  
 

120

100 -~ I
—O—Kneeangle 100 ’l’

80 h - '0 — Kneeangle 130

    

60 ..

Load (N)

40 —~

20 ~~

 

  

 

   

 

0 10 20 30 40 50 60 70
Vertical Deformation (mm)

 

 

 

Figure E.7 Load- Deformation Relationship of Thigh Structure for Two Knee Angles,
Subject No. 1

 

Subject No2, Thigh-Rigid Plate Test,

 

+Kneeang1e100 3
,o’

    
  

- O— Kneeanglel30

 

 

 

 

O 10 20 30 4O 50 60 70
Vertical Deforrmtion (mm)

 

 

 

Figure 13.8 Load- Deformation Relationship of Thigh Structure for Two Knee Angles,
Subject No. 2

 

 

102

 

Subject No.3, Thigh-Rigid Plate Test,

 

140

120 4~
—O—Knee angle 100 /
100 4*

—'.— Kneeang1e130 .

L08d(N)

 

 

 

 

0 10 20 30 40
Vertical Deformation (mm)

 

 

 

Figure E.9 Load- Deformation Relationship of Thigh Structure for Two Knee Angles,
Subject No. 3

 

Subject No.4, Thigh-Rigid Plate Test,

 

120
100 E» O
- O- - Knee angle 130 ’d
80 .r -—O—Knee angle 100 ‘ e /

Load (N)

 

 

 

6O

 

Vertical Deformation (mm)

 

 

 

Figure E.10 Load- Deformation Relationship of Thigh Structure For Two Knee Angles,
Subject No. 4

 

103

 

Subject No.5, Thigh-R1 gid Plate Test,

 

180

160 4

140 it +Knee angle 130
120 E +Knee angle 100

 

 

 

 

I a A
I 7’ f

50 60 70 80

0 10 20 30 40 _
Vertical Deformation (mm)

 

 

 

Figure E.11 Load- Deformation Relationship of Thigh Structure for Two Knee Angles.
Subject No. 5

 

Subject No.6, Thigh-Rigid Plate Test,

 

  
     

 

 

 

   

300
250 ~~
+Knee angle 100 .. ’.
/
A 200 " - '0 - Kneeangle 130
E
1:
a 150 ~~
.3
100 «~
50 ~
0 . 4. . . . 3
0 10 20 30 40 50 60 70 80
Vertical Deformation (mm)

 

 

 

Figure B. 12 Load- Deformation Relationship of Thigh Structure for Two Knee Angles,
Subject No. 6

104

 

Subject No.7, Thigh-Rigid Plate Test,

 

100

90 ~~ .
80 ‘” —O—Knee angle 100 ‘

70 -~ .. ’

60 — '0 — Knee angle 130 /

Load (N)

 

 

 

 

0 1 0 20 30 40 5 0 60 70
Vertical Deformation (mm)

 

 

 

Figure E.13 Load- Deformation Relationship of Thigh Structure for Two Knee Angles,
Subject No. 7

 

105

 

 

 

    
 
 
   
 

 

 

 

 

 

 

 

 
   
  
   
   

Knee angle 100
120 r
Part II
100 -. y = 2.9414x - 69.839
R2 = 0.9584
80 «—
Z
,3 6O ..
8
" 40 ,_ Part1
y = 0.9109x - 2.0431
2 =
2 0 0 R 0.9693
0 . a ,
0 10 20 , 30 4o 50 60 ' 70
Vertical Deformation [mm]
Knee angle 130
120
Part H
100 ~— y = 3.0396x - 59.557
1?.2 = 0.978
80 ~0—
Z
'3 60 .1-
0 Part I
..1
40 -. y =1.1324x - 2.4775
R2 = 0.9765
20 «

 

 

 

O 10 20 30 40 50 60
Vertical Deformation [mm]

 

Figure E.14 Best-Fit Lines Were Developed for Load-Deformation Curve of Thigh,
Subject No. 1

 

 

 

 

 
     
 
    

106
Knee angle 100
100 fl
9 l
m #-
P111111 ,
80 .. y =2m73x- 57.497 1
a’ =09719 l
70 <- ;
a) a.
E w ‘_
40 ..
300 Hm!
y=0.6799x-27244
20 .. a’ =0.9541
10 3*

 

 

 

Vertical Deforrrntion [rim]

 

 

 

 

Knee angle 130

 

   
 
    

120
Part 11
0 I
100 y=2.l433x-42.l77
R2 =0.9844
8O «»
E. 60 ..
B
.3 40 Part I
y =1.0354x — 2.8153
R2 =0.9803
20 ._

 

 

 

0 10 20 30 40 50 6O 70

Vertical Deformation [mm]

 

 

 

Figure E. 15 Best-Fit Lines were Developed for the Load-Deformation Curve of Thigh,
Subject No. 2

107

 

 

     
 
    

 

 

 

Knee angle 100
140
I
120 .. Part 11
y = 2.9235» 50.65

100 ~» R2 =0.9836
._ 80 t
E
‘0
g 60 ..

40 4» Panl

y = 1.1404x- 1.8835
2 _
20 4* R -0.95
0 * : .
0 10 20
Vertical Defo3gmtion [um] 40 50 6“

 

 

 

 

 

Knee angle 130
120
Part 11 q
100 ,_ y = 3.0523x- 43.674
R2 = 0.9909

 

 

4'
r

0 10 20 30 40 50
Vertical Deformation [rrm]

 

 

 

 

Figure E.16 Best-Fit Lines Were Developed for the Load-Deformation Curve of Thigh,
Subject No. 3

 

108

 

 

Knee angle 100

 

100
90 0 Part II
80 ._ y = 2.7283x - 64.079
70 w R2 = 0.9819

  
  
 
 
 
 

40 -~ Part1
30 -_ y = 0.8652x - 2.5519
R2 = 0.9428

Load [N]
M
o

  

 

 

 

0 10 20 30 40 50 60

Vertical Deformation [mm]

 

 

 

Knee angle 130

 

120
y = 2.8432x - 44.956

100 .. R2 = 0.9843

 
    

r

80‘

60 ~~

Load [N]

y = 1.4703x - 2.4633

40 4» R2 = 0.9801

    

20 ~~

 

 

A A
T v

   

0 10 20 30 40 50 60
Vertical Deformation [mm]

 

 

 

Figure E.17 Best-F it Lines Were Developed for the Load-Deformation Curve of Thigh,
Subject No. 4

 

 

 

 

 

 
 
  
    
  

 

 

 

 

 

 

 
 
 
 

109
Knee angle 100
140
120-» °
100 .
Part 11 e
y = 2.2785x - 44.265
5 3° ‘* R2 = 0.9827
E 60 ..
40 .. Part1
y = 0.8956x - 1.5367
R2 = 0.9804
20 -.
0 i - . . 2
0 10 20 30 40 50 60 70
Vertical Deformation [mm]
Knee angle 130
140
I
120 -
y = 2.5613x - 51.487
100 -. R2 = 0.981
E 80 -~
1:
8 60 « y=l.0946x-2.4566
._1

 

 

R2 = 0.9731

    

 

   

1

10 20 30 40 50 60 70
Vertical Deformation [mm]

1 1
l I

 

Figure E.18 Best-Fit Lines Were Developed for the Load-Deformation Curve of the

Thigh, Subject No. 5

 

 

 

110

 

 

Kneeangle 100

 

Part II
y = 2.8343x - 51.523
R2 = 0.9331

 
    
 
 
 

Part I
y = 1.206x - 2.5668
R2 = 0.9685

   

 

 

 

0 10 20 30 40 50 60
Vertical Deformation [mm]

 

 

 

Kneeangle 130

 

   
 
 

y = 4.0259x - 82.689
100 " it2 = 0.9836

y = 1.2436x - 2.7532
R2 = 0.9754

   

 

 

   
 
 

4 Ml J A
I T I'

0 5 10 15 20 25 30 35 40 45 50
Vertical Deformation [mm]

 

Figure B. 19 Best-Fit Lines Were Developed for the Load-Deformation Curve of Thigh,
Subject No. 6

 

 

 

111

 

 

  
 
 
 

 

 

 

 

 

 

 

 

  
 
     

 

 

    

 

Knee angle 100
120
Part II I
100 ~~ _.
y — 2.5359x - 64.84
80 .. R2 = 0.9697
Z
3 6° " Part 1
3 40 . y = 0.8074x - 2.3364
R2 = 0.9599
20 «t
0 4 . .
0 10 20 30 40 50 60 70
Vertical Deformation [mm]
Knee angle 130
120
y = 2.1941x - 40.695
100 ‘* R2 = 0.9898
80 ~-
2 60 ._
“g y = 1.0493x - 3.6822
2 =
3 40 .. R 0.9629
20 4~
0 . E . . .
O 10 20 30 4O 50 6O 70
Vertical Deformation [mm]

 

 

 

Figure E.20 Best-Fit Lines Were Developed for the Load-Deformation Curve of Thigh,
Subject No. 7

112

 

Knee angle 100

 

120

100 4»

   
 

+25 mm
+100 mm

80 4.

  

6()4-

Load [N]

40 ..

20 ~»

 

 

 

0 10 20 30 40 50

Vertical Deformation [mm]

 

 

 

Figure E.21 Load-Deformation Relationship for the Thigh Interaction with 43 Kg/m3
Foam Density, and with Two Different Thicknesses 25 mm and 100 mm, Knee angle 100°,
Subject No.1.

 

hhneanghrloo

 

160

l40 1*

 

 

 

 

 

 

 

 

0' v . .
0 10 20 30 40 50 60

\hrficaltkdbnnadon[nun]

 

 

 

Figure E.22 Load-Deformation Relationship for the Thigh Interaction with 44 Kg/m3
Foam Density, and with Three Different Thicknesses 25 mm, 50 mm and 100 mm, Knee
angle 100° Subject No. 1.

113

 

Knee angle 100

 

I60

140 ..

  
  
 

120 V
+100mm
'00 " ——50mm

  

—O—25 mm
80 ..

Loadi]

60 4r

40 ..

20 .»

 

 

 

0 iv.” e ‘ i
0 IO 20 30 40 50 60

Vertical Deformation [mm]

 

 

 

Figure E.23 Load-Deformation Relationship for the Thigh Interaction with 49 Kg/m3
Foam Density, and with Three Different Thicknesses 25 mm, 50 mm and 100 mm, Knee
angle 1000 Subject No.1.

 

Knee angle 100

 

200 T —O— 100 mm

I +50 mm
F1150 +
E. ' ——25 mm
a l
3 i

1

 

 

0 1 0 2 0 3 0 40 5 0 60
Vertical Deformation [mm]

 

 

 

Figure E.24 Load-Deformation Relationship for the Thigh Interaction with 51 Kg/m3
Foam Density, and with Three Different Thicknesses 25 mm, 50 mm and 100 mm, Knee
angle 100°. Subject No.1.

 

 

 

114

 

Knee angle 130

 

Load [N]

 

 

0 10 20 30 40 50

Vertical Deformation [mm]

 

 

Figure E.25 Load-Deformation Relationship for the Thigh Interaction with 43 Kg/m3
Foam Density, and with Two Different Thicknesses 25 mm and 100 mm, Knee angle 1300
Subject No.1.

 

 

 

 

 

Kneeangle 130
200
180 4E
l60 0 +50mm
+100mm
140 <~
— '—25 mm
'— 120 ""
E
'0 100 1r
8
'1 80 1»
60 4_ f
40 0
.l
0' "d i i v A +
0 10 20 30 4O 50 60 70
Vertical Deformation [mm]

 

 

 

Figure E26 Load-Deformation Relationship for the Thigh Interaction with 44 Kg/m3
Foam Density, and with Three Different Thicknesses 25 mm, 50 mm and 100 mm, Knee
angle 130° Subject No.1.

 

 

 

 

 

 

 

115
Knee angle 130
250
200 4
+50 mm
_ 150 . +100 mm
Z
“‘ — — 25 mm
.9
8 /
._1 100 ..
50 1 Me,
I" r
0 f‘ 1“! 4 4
0 10 20 30 40 50 60 70
Vertical Deformation [mm]

 

 

 

Figure E.27 Load-Deformation Relationship for the Thigh Interaction with 51 Kg/m3
Foam Density, and with Three Different Thicknesses 25 mm, 50 mm and 100 mm, Knee
angle 1300 Subject No. 1.

 

43 kgi'mJ Foam Density

 

120

Load [N]

 

 

 

0 . e 4 ¢ r
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0

Vertical Defo tmation [mm]

 

 

 

Figure B. 28 Effect of the Foam Thickness on the Foam Stiffness in Thigh-Foam
Interaction Test, Foam 43 kg/m3

 

116

 

Loale]

 

44 kg I'm" Foam Dens 11y

 

 

 

2‘” 7.—
180 0 //
——25mm I’
160 .. +50mm :
+100mm :
I40 4» '
120 j
5 10 15 20 25

Vertical Deformation [mm]

 

Figure E.29 Effect of the Foam Thickness on the Foam Stiffness in Thigh- Foam

Interaction Test, Foam 44 kg/m3 Subject No.1.

 

 

Load [N]

49 kglm‘ Foam Density

 

I401

120 7*

 

 

 

4 6 8 10 12 14 16 18

Vertical Defamation [rim]

 

Figure 1530 Effect of the Foam Thickness on the Foam Stiffness in Thigh- Foam

Interaction Test, Foam 49 kg/m3 Subject No.1.

 

 

117

 

 

51 kg/m3 Foam Density
250

+25 mm
200 ~» — — 100 mm,

 

150 0

Load [N]

100 v

50 .»

 

 

 

Vertical Deformation [mm]

 

Figure E.3l Effect of the Foam Thickness on the Foam Stiffness in Thigh- Foam
Interaction Test, Foam 51 kg/m3, Subject No. 1.

 

118

 

 

 

 

 

 

 

 

 

 

 

 

 

Knee angle 100.
250 7
l
i
200 ” ,l '
150 "If.
E "
'8 I,
3100~~ , ' ,. -
.—" ——Foam43kg/m3
.-'°' —-—Tnigh43kg/m3
50 _,. ..--' "“‘Total43kg’m3
,l '/ +Foam51kgn'8
-' +Tl'lighSlkg/m3 .
0 i f , "."Toml;lkg’nfi ;
O 10 20 3O 4O 50 6O 70
VerficalDeformation[mm]
Kneeanglel30.
120
'l
100 + , .-
.1
80 ~~ .-'v
:— ... ’.0'
E. /'
'8 60" '.""." g
3 ' x r
—-—-Foun43kg/n8 *
4o . —-——Tligh43kg/m3
I 'x' ----Total43kg/m3
20 i - +Foun51kg/m3
/ ’ +11%”: kg/rn3
/ “I-TotalSlkg/m'i
0 i if i l i
0 10 20 30 40 50 60

Vertical Deforrmtion [mm]

 

Figure E.32 Total, Thigh, and Foam Vertical Deformation versus Load, Subject No. 1
Thigh Interaction with Two Different Foam Density (43 kg/m3 and 51 kg/m3), 100 mm
Foam Thickness

 

 

 

119

 

Kneeangle 100.

+Tl’l'g151kgm3
~1» FoamSl kgms
——Foam43kg*m3
+mgr43 Igmz
----- Total mums
-:- mm. 51 lighfi

 

J;

8) 90 1(1)

 

 

 

 

 

Knee angle 130.

200 l»

n‘ - '
.I /
.— 150 ,1 n
E / .. “‘
1m 4. -
+myr43kg/nn
*Foum43kynfl
"'"Total43kg/nfl

 

+ FounSl Its/n13
~I~ TlighSl Its/m3
' '3' 'Total 5| kme

 

1
V,

0 l 0 20 3O 4O 50 60 70 80

Vertical Deformation [mm]

 

Figure E.33 Total, Thigh, and Foam Vertical Defamation versus Load, Subject No. 2
Thigh Interaction with Two Different Foam Density (43 kg/m3 and 51 kg/m’), 100 mm
Foam Thickness

 

120

 

 

Knee angle 100.

 

180

’
, ’—-—- Foam43 kg/rn3

Load [N]

+ FoamSl kg’rrB
- a - Total 51kgfn13
-- Total 43 kg/nfi
—-—nigr43 Kgmfi
+Tli615|ktm3

 

 

O 10 20 3O 40 SO 60 7O 80
Vertical Deformation [mu]

 

 

Knee angle 130.

 

+1‘nighsuyno
—-—'l'ligh43kymB
—-—Foam43 kgms ;

 

+Foam51kg/nfi
--I-Total Slkg/n'B (
- -- -Total43 ngmS

 

0 10 20 3O 40 50 6O 70

Vertical Deformat'nn [mm]

 

 

 

Figure E.34 Total, Thigh, and Foam Vertical Deformation versus Load, Subject No. 3
Thigh Interaction with Two Different Foam Density (43 kg/m3 and 51 kg/m3), 100 mm
Foam Thickness

 

121

 

 

 

 

 

 

 

 

 

 

 

  
   

 

   

 

 

KneeangleIOO.
120 a a mi
‘-
1m 41- .
.I’ ' 3
30 t» "r i
1
z .0"
360 .~ ' +me51kglnfl
I 1 - " +11ig151kgrms
40 ”F ~|- Totaisug'mi
,' —-—w43ks/ms
20 ’ ,, -—-—me43kg/n13
,,/~ -~--~Total43kg/3
0 V“- ; t f ,L
O 10 20 30 40 50 60 70 80
Vental Defonmtion[mn]
Knee angle 130.
120 1
1m d .d' 1
. l
r-t 80 d " F 1
E ’ .- —-—Foam43 krdm3 1
'0
g 60 -—Tli7gh43kgm?
40 ------ Total43 kg/m3
+Foam51kng
20 +Th'd151kgm3
mItTota151kg/m3
o i , i i i i i
0 10 20 30 40 50 60 7O 80

Vertical Deformation [nm]

 

Figure E.35 Total, Thigh, and Foam Vertical Deformation versus Load, Subject No. 4
Thigh Interaction with Two Different Foam Density (43 kg/m3 and 51 kg/m3), 100 mm

Foam Thickness

 

 

 

122

 

 

Knee angle 100.

 

  
 

 

 

 

 

 

 

  
 

 

 

E.
g I Foam. 51 kgim3
..i +Thigh. 51kg/m3
' ‘ ‘ Total. 51 kg/m3
--— Foam. 43 kgfmJ
+ Thigh. 43 kg-‘mJ
-'" Total. 43 kg/m3 .i
i
0 f ¢ ¢ . . e I
0 10 20 3O 40 50 60 7O 80
Vertical Deformation [mm]
Knee angle I30.
180 I
I60 . ." i
140 i E
1201~ 4
'2 100 j I
v a
E) 80 -‘ —-—Foam 43 kg/m3 1
60 —-—M 43 kg/m‘i i
- -- - Total 43 kg’nfl 3
40 - a - Total 51 its/mi 1
20 +Foam5! kg/m‘i
+11%: 5| its/m3
0 Y r a. .
0 10 20 30 40 50 6O 70 80
Vertical Deformat'nn [mm]

 

Figure E.36 Total, Thigh, and Foam Vertical Deformation versus Load, Subject No. 5
Thigh Interaction with Two Different Foam Density (43 kg/m3 and 51 kg/m3), 100 mm
Foam Thickness

 

 

123

 

 

 

 

 

 

 

 

Kneeangle 100.
200 f
’/
la) 1‘ i
/
I60 t /
140 1*
l .
__ 120 v , I ,
Z ’ r
'0 1m ‘* Ix ’ .
8 ’ , ——Foam43 kgm3
_J a) ‘F x I
1’ . ’ *M-flkgm}
I ,’
so «» ," ,' -- ~Toul43kgm3
I I I.
40 0 ’/-‘ +Foam5lkgm3
w r” ’ +ntgisikgms
20 ‘ .z‘
4" -I- Totalsntgnt}
01 f .
0 10 20 3O 40 50 60 70 80
VerticalDefomaIion[mn]
Knee angle 130.
160 ..
F
140 t I
I
120 “ 1
1
_ 100 .. i
a E
'1: 80 “ - l
g l
60 - _ , ,, ' —-—M43 W l
-- ' ‘ Foarn43 kg/m3 l
40 - - -Total43 kg/m3 I:
+Foam51kg/m3 !:
20 +ntigh51kg/m3 l
-- -Tota151kg/m3 l
o , i
0 10 20 40 50 60

 

 

  

 

 

 

Vertical Defotifmion [mm]

 

 

 

Figure E.37 Total, Thigh, and Foam Vertical Deformation versus Load, Subject No. 6
Thigh Interaction with Two Different Foam Density (43 kg/m3 and 51 kg/m3), 100 mm
Foam Thickness

124

 

 

Knee angle 100.

/' ’4'“ ' " +Faam43 lag/m3
.' - mgt43kg’n13
- -- Total43 Its/n13

Load [N]

1* FoamSl ltgm3
~I~1higL51|tgxm3
' .' TotalSl kg/nfl

 

w

0 10 20 30 40 50 60 7O 80

Vertical Defamation [mm]

 

 

 

Knee angh 130

  
   

*Foamlrmeangle 130
""‘Tatalkmeanglelw
+1h'dtkmeugle 130
"I' Faanaceude 100
“I“ Thighlcmeardeloo
"I”Tatal lcneeangeloo

m L 4
- - T

O 10 20 30 40 50 6O 70

Load [N]

 

Vertical Defamation [mm]

 

Figure E.38 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 7
Thigh Interaction with Two Different Foam Density (43 itg/rn3 and 51 kg/m3), 100 mm
Foam Thickness

 

 

125

 

Knee angle 130.
120* . . ._-.

  
   

l
100*" ‘.
I /
I _.
SOT .I'
1 ,I'
2' l ’
E °°=*
.1 1 -—°—Foam25mn
——‘-"Tla‘gh25m
""‘TotalZSmm

+Foam100mm
+ Th‘yi 100nm
' .' Total l00mm

4O 50 60
Vertical Deformation [mm]

 

 

Figure E.39 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 1,
Thigh Interaction with Two Different Foam Thickness (100 mm and 25 mm), and 43
kg/m3 Foam Density

 

Knee angle 100.

140 T' "

 

Load [N]

Thigh 25 mm
—Faam 25 mm
' "' Total. 25 mm
+Thigh. 100 m

"i- " Foam 100 mm

 

' 1' 'Total 100 mm

 

Am

0 IO 20 30 40 50 60 70 80

Vertical Defamation [mm]

 

 

 

Figure E.40 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject No. 2,
Thigh Interaction with Two Different Foam Thickness (100 mm and 25 mm), and 43
kg/m3 Foam Density

 

126

 

 

Knee angle 130.

 

+Faam. lOOmm
' .‘ Total.100mm
+Thigh.100mm

—-- Foam 25 mm

Load [N]

- " 'Tatal, 25 mm
*Thigh, 25 mm

 

 

 

0 10 20 30 40 50 60 70

Vertical Deformation [mm]

 

Figure E.4l Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 3,
Thigh Interaction with Two Different Foam Thickness (100 mm and 25 mm), and
43 kg/m3 F aam Density

 

 

Knee angle 130.

 

  
 

100

.-
90 .1“ v -
80 J»- ‘0‘.
7o — '
60 ‘¥ 0
50 1 .' —--—Faam25mm

I —-—Thigh,25mm
-' - Total. 25 mm
+Thigh,100mm
+Faam100mm
- -I’-TataL100mm

4O
30
20
10

 

Load [N]

 

 

0 10 20 3O 4O 50 60 70 80

Vertical Defamation [mm]

 

Figure E.42 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 4,
Thigh Interaction with Two Different Foam Thickness (100 mm and 25 mm), and
43 kg/m3 Foam Density

 

 

127

 

 

 

 

  
 

 

 

 

Knee angle 130

90 .—

80 ~ /‘ v’
t :
70 T .’ -
.— 60 "
t.z_. 50 ‘ +Foam 100mm
g 40 - +ThigthOmn
t-1 30 "' -— Total 100 mm 1
20 Foam25 nm
10 “"‘Tatal,25mm :
0 i . i I

O 10 20 3O 4O 50 60

Vertical Defamation [mm]

 

 

Figure E.43 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 5,
Thigh Interaction with Two Different Foam Thickness (100 mm and 25 mm), and

 

43 kg/m3 Foam Density
Knee angle 130.
160 T — »- -~—» ,, ,. . .
g /
not /
z +Thigh,100mm
E ". Foam25mn
—~—-ThithSmm
-----Toutizstmt

“I" Foam 100 mm

' ‘l‘ 'Tatal, IOO nan

 

50 60

30
Vertical Defamation [mm]

 

Figure E.44 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject No. 6,
Thigh Interaction with Two Different Foam Thickness (100 mm and 25 mm), and 43
kg/m3 Foam Density

 

128

 

 

Knee angle 130.

 

  
  

 

 

100 .
90 T” ll
80 “T I ’
7O ‘—
Z 60 T
g 50 d —-—Foam 25 mm
._1 40 ——--— Thigh 25 mm
30 —- Total25 mm
20 +Faam100 m
—I- Total 100 mm
10 +Thigh 100 mm
o a i : .

 
 

 

O 10 20 30 40 50 60 70

Vertical Defamation [mm]

 

Figure E.45 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject No.7,
Thigh Interaction with Two Different Foam Thickness (100 mm and 25 mm), and
43 itg/rn3 Foam Density

 

 

 

  
 

 

 

120
l
. 4
100 ‘0' . ‘ 1
. r'
. ', a i
'— 80 .0. .'.‘. " 1
a ..i"
g 60 .4».
._J +Faam knee angle 130 5
40 + Th'gh knee angle 130 §
- -l - Total knee angle 130 f
—-—Faam knee angle 100 1
20 —— Thigh knee angle 100 i
- - -Totalkneeangle100 1
l
0 I Y V Y I
0 10 20 30 4O 50 60

Vertical Defamation [mm]

 

Figure E.46 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 1,
Thigh With Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and A3 kg/m3 Density)

 

 

129

 

 

250 M--- .._....I

0
'0
200 + .,. .'
do. .-
. I". I.

 

 

 

_ 150 .. . .
Ea .' o. 1
'° . ' l
100 w" x o ’ I' o ' l
.' +Foam knee angle 100
. , ' .I ' + Thigh knee angle 100 .
50 l . - ' ' ' 1' 'Tatal knee angle 100 !
1 - ‘ ' Foam knee angle 130 i
-—— Thigh knee angle 130 j
0 ,_,/- i I + ' ' " ' Total knee angle 130 i
0 IO 20 30 40 50 6O 70 80

Vertical Defamation [mm]

 

 

 

Figure 4.47 Total, Thigh, and F aam Vertical Defamation Versus Load, Subject No. 1,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 51 kg/m3 Density)

 

 

 

 

 

140 r“:
I
120 + /r [I l
I ,'
100 “T I I
a ,r’ r
E, 80* ,I J
a I I"
O 60 «r ’1 1‘ +Faamkmean¢100
s—l ’ ’1 +11% kmcmmo
40 +, ,’ X --— Totaikmeangieioo
,’ *Thgltkmeagb 130
20 ' —-—Foamkmeargkl30
O 1 _: A I A -- TataLJkneeargEBO
0 20 40 6O 80 100
VerticalDefarmation[nm]

 

 

 

Figure E.48 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 2,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 43 kg/m3 Density

130

 

 

Load [N]

  
 

+m‘gt kme angJe IOO
+ Faemkncearue IOO
""Total.kneeardelm
*mehteeamle I30
" high. knee ange I30
‘ "‘ Total.kneeangel30

 

0 10 20 30 40 50 60 70 80

Vertical Deformtionhrln]

 

Figure E.49 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 2,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam ( 100 mm
Thickness and 51 kg/m3 Density)

 

 

 

120 + /'/.

100 '11' ,
/

E 80 L
'3 --—Total.kneeangle 130
3 601— +Tatalkneeangb100
’ —-—Faam, kneeangle 130
40 + ,, / +Foam,1tneeang1e 100
*Thigiikrieeangi: 130
20 ‘ +Thighkneeangle 100

1 1 J
Y T 1

 

O 10 20 30 40 50 60 70 80
Vertical Defamation [mm]

 

 

 

Figure E.50 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 3,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 43 kg/m3 Density

131

 

 

 

     
     
   
   

 

 

i
l
I
180 l
160 1" *nigiimeeangieno /.- ’. 1
140 4~ + Th'gtkmeargelm 1' f 1
fl —-—Foami<meang1e13o ' .’ g
t— 120 +Faamkmeargelm ' §
E. 100 ~~ -a -Totaiimeeangeioo g
'g 80* - "Totaiitrneangeno I
O
.1
60 * .
4o . ;
20
0 i
0 10 20 30 40 50 60

Vertical Defamation [nm]

 

 

Figure E.51 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 3,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 51 kg/m3 Density) -

 

 

 

120

f ,I‘ '
I00 ‘1 .’ I l . 1
I ’ ‘
/ / I 1
x I / 1
"' II I ' 1
I ,
I

 

 

 

80 ‘1" / I I
I
/ I I
._. / I I ’
.2. a
60 ‘1 I
3 , ’ , ’ .
I
l , X
I
I " +Thl'h. knee angle IOO
40 "’ I I
/ I ’ g ’ +Foam. knee angle 100
I I ’, ' —I— TotaL knee angle IOO
’
20 —-——- Foam. knee angle 130
] -—Thrgb.knee angle 130
I — — TotaL knee angh 130
0 r; r
0 10 20 30 40 50 60 70 80

Vertical Defamation [mm]

 

Figure E.52 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 4,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 43 kg/m3 Density)

 

 

132

 

 

 

1m 4)-

  
 

: 50.. ——Founlaueadel30 5

E ——m¢a|mauem f
40., - -- Totalluncagklw
+Fommauemo

 

+1h'ghlau-gcloo
--I~Toulkmeagh loo

 

 

I
l
I
l
x
I Y Y l
0 10 20 30 40 50 60 70

 

Figure E.53 Total, Thigh, and F aam Vertical Defamation Versus Load, Subject No. 4,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm

 

 

 

 

 

Thickness and 43 kg/m3 Density)
Kneeangle 130.

180 i

160 ,_ . —— Totalkneeangb130 ’ -
140 I —a— TataLkmeangblOO /"/
120+ —-—’Ihigh,kmeangbl30 I’"

Z 100‘ +Tbistumeeansbloo {/11 ’
E 80 F +Foamkneeang|el30 I j
60 I +Faamkmeargh 100 3,

4o

20 f :

o —- r I 1 l + 1 I
0 10 20 30 40 50 60 70 80

Vertical Defamation [mm]

 

Figure E.54 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 5,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 51 kg/m3

 

 

133

 

 

 

 
 
 

+Foamkmeangle100 i
+Thig'kkl’neargk100 / I/
—a— TotalkmeangblOO ’ 3
—-—Faamkmeargll30
—-—Thigh,kneeangbl30 ”,t
------Total,kmeangbl30 ~'

 
   
   
   

 

l - l I

0 10 20 30 40 50 6O 70 80
Vertical Defamation [mm]

 

 

Figure E.56 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 5,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm

 

 

 

 

 

 

 

Thickness and 43 kg/m3 Density)
250
. I
200 ~— '. . .n’
150 ~- 3‘ .-
I—o .' ‘-o
a I ‘ fl .9 o
g 100 “h . - ‘ ° Foam knee angle I30
__1 g .' Thigh knee angle I30
- -- - TatalKnee angle 130
50 ' +Faam knee angle IOO
+Thigh knee angle 100
' g .’ - -I - Totalknee angle 100
0 4- i- : l j; TL % 41
0 10 20 3O 40 50 60 70 80

Vertical Defamation [mm]

 

 

Figure E.57 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 6,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 51 kg/m3 Density

 

134

 

 

 

’ -— TolaLkneeangbBO
—n— TataLkneeangthO
—-—Foamkmeangie13o
+Foamkneeangh100
—-—Th7ghkmeanglel30
+Thighkneeangle100

l

I l

Load [N]

 

 

 

f

0 10 20 3O 40 50 6O 70 80

Vertical Defamation [mm]

 

Figure E.58 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 6.
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 43 kg/m3 Density)

 

 

 

 

IOO ;
9o 4 x l
80 ~~ '
7o ~~ '3“

.— 60 w

E.

'o 50 Faamkmeange 130

3 40 ~~ - --Tatalkneean§el30

  
 

 

*Mhieeargh I30
+Faam.kneeargk 100
—I— Th'thmeeargb lm
- -I -Total kmeange IOO

L L L
T l

 

0 IO 20 30 40 50 60 70

Vertical Deformation [nun]

 

Figure E59 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject Na. 7,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 43 kg/m3 Density)

 

 

135

 

 

 

 

 

140
. l
120 * /'. .
100 “m, 1'."
Z 80 .4» .. O. .."
.503 60 l , . x. . . Faom knee angle 130 5
._l l ' —-—-—Thighkneeangk 130 E

- -- -Tatalkneeangle I30

 

40
+ Faam knee angle IOO ;
20 + Thigh knee angle IOO ;
- -I-Totalkneeanglel00 ’
0 “" t m i a ‘
0 10 20 3O 40 50 6O 70 80
Vertical Defamation [mm]

 

Figure E.60 Total, Thigh, and Foam Vertical Defamation Versus Load, Subject No. 7,
Thigh with Two Knee Angle 100° and 130° Interaction with One Foam (100 mm
Thickness and 51 kg/m3 Density)

 

Load[N]
29 § 2 § [g

C

§§§

Load [N]
§

ES

0

136

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Knee angle 100°
i l
l i
I ;
! i
i i a
X. I
l a
0 10 20 30 4O 50 60
Vertical Defamation [um]
Knee angle 130°
1 i i ‘ //
i I i l
I : ‘ l )f '
l / g
l 4 / ,:
1 s
0 10 20 3O 40 50 60 70 80
Vertical Deformation [rrm]

Figure 13.6] Vertical Defamation of Thigh versus Load at Node 3,3 and 3,4, Subject No.

l, Foam 61, Thickness 100 mm. Knee angles 100° and 130°

137

Knee angle 100°

 

160
140 s»

120

IOO ‘—

Laad [N]
00
o

 

 

 

 

 

 

+ Node 3,3 + Node 3,4

    
  

 

 
 

I
r

10 2O 30 40 50 6O 70
Vertical Defamation [mm]

Knee angle 130°

 

Load [N]

 

   
  

 

 

+ Node 3,3. + Node 3,4

 

 

 

 

 

 
 

i
T

10 20 30 4O 50 60 70
Vertical Defamation [mm]

Figure E.62 Vertical Defamation of Thigh versus Load at Node 3,3 and 3,4, Subject

No.2, Foam 61, Thickness 100 mm. Knee angles 100° and 130°

138

Knee angle 100o

 

 
 

 

 

 

, + Node 3,4 +Nade 3,3

    

 

 

 
 

 

 

4L
Y

O 10 20 30 40 50 60
Vertical Defamation [mm]

Knee angle 1300

 

   

 

 

, +Nade 3,4 +Node 34,3

 

 

 
 

 

 

 

0 10 2O 30 4O 50
Vertical Defamation [mm]

Figure E.63 Vertical Defamation of Thigh versus Load at Node 3,3 and 3,4, Subject
No.3, Foam 61, Thickness 100 mm. Knee angles 100° and 130°

139

Knee angle 1000

 

120
100 e

80 * +Node 3,4 +Nade 3,3

 

 

 

 

Load [N]

 

 

 

 

l l
T T

O 10 20 3O 4O 50 60

Vertical Defamation [mm]

 

      
 

 

 

 

 

 

 

 

Kneeangle130°

100

m4-
Z 60 +NOCb3,4 +Node3,3
.3 .
o 40
.4

20

O

0 10 20 3O 4O 50 60
Vertical Defamation [m]

Figure E64 Vertical Defamation of Thigh versus Load at Node 3,3 and 3,4, Subject
No.4, Foam 61, Thickness 100 mm. Knee angles 100° and 130°

140

Knee angle 100°

 

   

 

+Node 3,3 + Node 3,4

 
  

 

 

120 -

 

Load [N]

 

 

 

0 10 20 3O 4O 50 60 7O 80

Vertical Defamation [mm]

Knee angle 130°

 

fl
0\
O
l
T
l

140 ~~ - -— ~

 

y—a

N

O
l

 

ML +Node3,4 +Nade3,3 i

 

 

 

 

0 10 20 3O 40 50 6O 7O 80
Vertical Deformation [mm]

Figure E.65 Vertical Defamation of Thigh versus Load at Node 3,3 and 3,4, Subject Na.
5, Foam 61, Thickness 100 mm. Knee angles 100° and 130°

141

 

 
  

   

 

 

 

 

   

 

 

 

   

 

  
   

Knee angle 1000
240
220 ~—
200 -_
180 ~—
160 - +Node 3,4 +Node 33
E 33
1:
8 100
“'1 8O
60
40
20 a
0 , . 4 A)
o 10 20 30 4o 50 60 70
Vertical Deformatim [mm]
Knee angle 1300
220
180 e—-~—--e—»~e-~e—-----s-er _

 

 

 

‘60 ‘ +Node 3,4 + Node 3,3.

 

  

 

 

 

O 10 20 30 4O 50 60
Vertical Defamation [mm]

Figure E.66 Vertical Defamation of Thigh versus Load at Node 3,3 and 3,4, Subject
No.6, Foam 61, Thickness 100 mm. Knee angles 100° and 130°

142

Knee angle 100°

 

140
120 ~-
100 ~— - ~

 

 

+Node 3,4 +Node 3,3

 

 

 

 

 

 

 

   

 

 

 

 

 
 

E
E3
O 110 20 310 40 5.0 60 70
Vertical Deformation [mm]
Knee angle 1300
140
120 ~~
100 a . -h a a .
Ego - ,, +Node 3,4 +Node 3,3 w
“s? so -
i—l 40 g
20 —

 

 

 

O 10 20 3O 4O 50 60 70
Vatical Defanmtian [mm]

Figure E.67 Vertical Defamation of Thigh versus Load at Node 3,3 and 3,4, Subject
No.7, Foam 61, Thickness 100 mm. Knee angles 100° and 130

143

 

 

 

 
   

 

  
   
 
 

 

    

 

 

 

  
 

    
 

 

 
 
  

 

 

 

 

 

 

 

 

120 i
l
'i
[00 1* I
l
!
so 0 Foam Part n l
y=4.o97x+35.34' ‘
,_, R2 =0.9781 g l
Z l i
i; 60 .. l
g T\ngh Part n ‘l
._l Foam Pm! ly=4.2963x -80_879 :
40 0 y = l2.538x +6.8818 : R2 = 0.9784 -l
R2 =0.929 ; .5

20 0 Thigh Part r

y = l.449lx - 3.5867
R2 =0.9Sl6 I
at y : . _
0 5 IO 15 20 25 30 35 4o 45
Vertical Definmation [nan]

 

Figure E.68 Linearization of Load-Vertical Defamation Curves for the Thigh and Foam.
Foam 43 kg/m3, Knee Angle 100°, Subject No. l

 

 

 

 
 
   
 
  
  

 

 

 

 

 

 

 

  
 
  

 

 

 

 

   

 

 

 

 

 

 

140
120 .. Part ll 0
y a 3.4964): + 31.5364}
R1 = 0.7566
100 «~
,_ 80 0 Thigh Part n l
E y=3.3272x-83.998|
'° R2 = 0.9887 .
3 60 4»
4° " Partl
y =10.125x + 6.4268
20 4 R: = 0-9109 Thigh Part I
y = 0.78417: - 2.6762
R2 - 0.9437
0 . Y , s
0 lo 20 30 4o 50 60 70
Vertical Defamation [mm]

 

 

 

Figure E.69 Linearization af Load-Vertical Defamation Curves far the Thigh and Foam.
Foam 43 kg/m3, Knee Angle 100°, Subject Na. 2

 

144

 

 

 

 

 

 
   

 

 

 

 
  
  

 

 

 

 
  

 

 

 

  

 

 

 

 

 

I40
Foam Part ll
.0. = .
120 y 3.7383x + 28.951 Thigh Part [1
R2 - 036% y = 4.3524x - 67.068
100 ~~ R2 =0.9757
l
"" 80 +
E
E ,0 ..
40 4 ' Foam Part I
y = l l.l4lx +0.0545
20 R2 = 0.9999 Thigh Part I
.s y = 1.2952x - 3.2035
R2 = 0.9193
0 I ~ ‘
0 5 IO 15 20 25 30 35 40 45

Vertical Defamation [run]

 

Figure E.70 Linearization of Load-Vertical Defamation Curves for the Thigh and Foam.
Foam 43 kg/m’, Knee Angle 100°, Subject Na. 3

 

 

 

   
 
   
 
 

 

 

 

 

 

 

 

 

 

 
  

 

  

 

 

  

 

 

 

 

120
100 «r .
Foam Pan ll
80 ~r y = 5.4615x + 27.609
_ I R2 = 0.9348
E.
E 60 4" Thigh Part 11
y = 2.2796x - 52.466
R2 = 0.9748
40 Foam Part I
y = 28.8687: + 0.6198
20 R2 = “-9327 Thigh Part 1
y = 0.77651: - 2.1377
R2 = 0.9713
0 . ¢ 4 .
0 10 20 30 40 50 60 70

Vertical Defamation [nan]

 

 

 

Figure E.7l Linearization of Load-Vertical Defamation Curves for the Thigh and Foam.
Foam 43 kg/m3, Knee Angle 100°, Subject No. 4

 

145

 

Load [N]

 

120

 

lOO «-

80 n»

60 o

 

40

20

' y =33.212x + 6.8261

 

 

 

 

 

 

 

 

Thigh Part 11 °
Foam pan] y = 2.82174x - 72.701
y = 5.9933x + 49.576 R = 0.9759
0 R2 = 0.9303
0
L

 

Fpam Part 1

R2 = 0.8477

   
 
 

 

 

 

Thigh Part 1
y = 1.23l2x - 5.2252
R2 =0.9588

 

 

 

10 20 30 40 50 60

Vertical Defamation [run]

   
   
 
 
 

 

7O

 

Figure E.72 Linearization of Load-Vertical Defamation Curves for the Thigh and Foam.

Foam 43 kg/m3, Knee Angle 100°, Subject No. 5

 

Load[N]

160

 

14o 4-

100 4»

80 4.

60 ..

40 1’

20 4.

 

 

Foam Part 11
y = 4.359x + 49.672
R2 = 0.8049

0

   
   
    

 

 

    
  
    
 

 

 

Thigh Part 11
y =5.521x - 127.75
R2 =0.9679

 

 

 

O

 

 

   

 

 

 

 

 

 

Foam Part 1
y = 14.4321: + 5.2693
R2 =0-9154 Thigh Part 1
y = 1.3772x - 2.0398
R2 = 0.9841
5 10 15 20 25 30 35 40 45

Vertical Deformation [run]

50

 

Figure E.73 Linearization of Load-Vertical Defamation Curves far the Thigh and Foam.

Foam 43 kg/m3, Knee Angle 100°, Subject No. 6

 

 

146

 

 

 

 

 

  
  

 

   

 

 

 

80
70 ._ f Thigh Part 11 i
Foam Part 11 y=2.6114x-52.315!
60 n y = 8.66441: + 24.814 1 R2 = 0.9972
R2 =0.963
50 .,

 

 

 

 

 

 

 

 

 

 

 

Thigh Part 1
10 y = 0.9278x - 3.1003
R2 = 0.9573
0 Y Y ' 5 L
0 5 10 15 20 25 30 35 40 45 50

Vertical Defamation [nan]

 

 

Figure E.74 Linearization of Load-Vertical Defamation Curves for the Thigh and Foam.
Foam 43 kg/m3, Knee Angle 100°, Subject Na. 7

 

147

 

Knee angle 100

 

0.9

0.8 «-

+Thigh-Foam
+ Thigh-Rigid Plate

 

 

 

 

 

 

 

 

 

 

 

 

E
E
E.
'8
3
0 i * * r
0 10 20 30 40 50 60 70
Vertical Deformation [mm]
Knee angle 130
0.9
0.8 1»
o_7 4. —O—Thigh-Faam
0 6 +Thigh-Rigid Plate
2
'8
.3
0 10 20 30 40 50 60
Vertical Defamation [mm]

 

 

 

Figure A.75 Load Nomalizatian for Thigh-Foam (43 kg/m3 Foam Density) Interaction
and Thigh-Rigid Plat Tests, Subject Na. 1

 

148

 

 

 

 

 

 

 

 

 

 

 

 

 
    

 

 

 

Knee angle 100
1.2
1 .
+ Thigh-Foam
0.8 ., + ThighoRigid Plate
E
E
E.
'0
8
._l
0 10 20 30 40 50 60 70 80
Vertical Defamation [mm]
Knee angle 130
0.8
0.7
0.6 1 + Thigh-Foam
,__ 0 5 + Thigh-Rigid Plate
2 0.4
~13
g 0.3
0.2 4»
0.1
O 1 1 i Y .7 4.
0 10 20 30 40 50 60 70
Vertical Defamation [mm]

 

 

Figure A.76Laad Nomalizatian for Thigh-Foam (43 kg/m3 Foam Density) Interaction and
Thigh-Rigid Plat Tests, Subject No. 2

149

 

Knee angle 100
0.9

0.8 4
0.7 ._ +Thigh-Foam

0.6 q, + Thigt-Rigid Plate

 

 
 
  

0.5 «»
g 0.4 -»

3 0.3 .»

N/mm]

 

 

 

 

0 10 20 30 40 50 60
Vertical Deforrmtian [mm]

 

 

 

 

Kneeange 130

 

 
 
 

+ ThigT-Foam
+ Thigi-Rigid Plate

 

 

 

 

0 10 20 30 40 50
Vertical Defamation [nan]

 

 

 

Figure A.77 Load Nomalizatian for Thigh-Foam (43 kg/m3 Foam Density) Interaction
and Thigh-Rigid Plat Tests, Subject Na. 3

150

 

 

Kn'ee angle 100
0.7 I

 

0.6 «~
+Thigh-Faam

0.5 4» + Thigh-Rigid Plate

.°
A

Load [N/mm]
.°
W

.O
N

0.1 «»

 

 

0 10 20 30 40 50 60
Vertical Deformat ion [mm]

 

 

 

Knee angle 100
0.8

 

 

 

0.7 3»
0.6 I
0.5 ..
0.4 ..
0.3 v
0.2 4

+ Thigh-Foam
—I-— Thigh-Rigid Plate

Load [N/mm]

0.1 .1

 

0 10 20 30 4O 50
Vertical Deformation [mm]

 

Figure A.78 Load Nomalizatian for Thigh-Foam (43 kg/m3 Foam Density) Interaction
and Thigh-Rigid Plat Tests, Subject Na. 4

 

 

151

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Knee angle 100
1.4
1.2 ~»
+Thigh-Foam
._. 1 " +Thigh-Rigid Plate
2
'8
3
t
, . ,
0 10 20 30 40 50 60 70 80 -
Vertical Defomat ion [mm]
Kneeangle 130
0.9
0.8 4» .
0.7 +Thigr-Foam
0.6 + Thigh-Rigid Plate
E 0.5
E
:1 0.4
8
._i 0.3
0.2
0.1
0 f e i f i .
0 10 20 30 40 50 60 70
Vertieal Defamation [rmn]

 

 

Figure A.79 Load Nomalizatian for Thigh-Foam (43 kg/m3 Foam Density) Interaction
and Thigh—Rigid Plat Tests, Subject Na. 5

 

152

 

Knee angle 100

 

0.8 «t

Load [N/mm]

 

 

0.9 «t

+ Thigh-Foam
+ Thigh-Rigid Plat

 

 

20 30 40

 

 

 

 

 

 

 

 

 

 

0 50 60
Vertical Defamation [mm]
Knee angle 130

0.9

0.8 ~

0.7 .. —-O—Thigh-Rigid Plat

+Thigh-Faam
2.
10 15 20 25 30 35 40 45 50

Vertical Deform at ion [mm]

 

 

Figure A.80 Load Nomalizatian for Thigh-Foam (A3 1tg/m3 Foam Density) Interaction

and Thigh-Rigid Plat Tests, Subject Na. 6

153

 

 

Knee angle 100
0.8 I

0.7 .—
l

0 6 0 +Thigh-Foam
+Thigh-Rigid Plate 1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

E”
E
._Z_.
3
0 10 20 30 40 50 60 70
Vertical Defamation [mm]
Kneeangle 130
0.8
0.7
06 t Thigh
_ ' +ThighRigid Plat
Z
'0
:6
o
._1
0 10 20 30 40 50 60 70
Vertical Deformation [mm]

 

 

Figure 4.81 Load Nomalizatian for Thigh-Foam (A3 kg/m3 Foam Density) Interaction
and Thigh-Rigid Plat Tests, Subject No. 7

154

 

 

Foam-Thigh Interaction Contour.
Side View - sub.1,
Reaction Farce lOON

 

 

 

 

 

 

 

 

 

 

 

-10 \\
E -15
20 --------------------- A
——> Toward the knee
-25« -
-30 1
SI 32 S3 S4

 

Figure A.82 Side View of Foam-Thigh Interaction Contour, Subject No. l

 

 

Foam-Thigi Interaction Contour
Side View . sub. 2
Reaction Force 120 N

' > TowardtheKnee

 

SI 82 S3 S4

 

 

 

Figure A.83 Side View of F oam-Thigh Interaction Contour, Subject No. 2

155

 

Foam-Thigh Interaction Contour
Side View sub. 3
Reaction Force 122 N

 

\

\ \\

 

 

 

 

 

 

 

 

 

 

-20 x
3 ———p Toward the knee
-30 a v l
5] S2 S3 S4

 

 

 

Figure A. 84 Side View of F oam-Thigh Interaction Contour, Subject No. 3

 

 

 

 

 

 

 

 

 

Foam-Thigh Interaction Contour
Side View. Sub. 4
Reaction Force96 N
0 I
-5 ,
B W
-10-~ *
E -15 -------------
-20- ....................
25 ——‘> Toward the Knee A
-30 j 1
S] 82 S3 S4

 

 

 

Figure A.85 Side View of Foam-Thigh Interaction Contour, Subject No. 4

156

 

 

Foam-Thigh Interaction Contour
Side View sub. 5
Reaction Force 124 N

_ __,> , Toward the Knee _____ A

 

1
SI 82 S3 S4

 

Figure A.86 Side View of F cam-Thigh Interaction Contour, Subject No. 5

 

Foam-Thigh Interaction Contour
Side View sub. 6
Reaction Force 124N

mm

A

 

]
SI 82 S3 S4

-—-—-} Toward the Knee

 

 

 

Figure A.87 Side View of Foam-Thigh Interaction Contour, Subject No. 6

 

157

 

Foam-Thigh Interaction Contour
Side View. sub. 7

 

 

 

 

 

 

Reaction Force 72N
0.;
/
B 6* <
A
S -10 ----- - , - ~ - -
___> Toward the Knee
-151
-20 1
SI 82 S3 S4

 

 

 

Figure A.88 Side View of Foam-Thigh Interaction Contour, Subject No.7

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