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This is to certify that the
thesis entitled

EFFECTS OF THREE-DIMENSIONAL GEOMETRY ON
PENETRATION AND PERFORATION RESISTANCE

presented by

GEORGE JOSEPH COPPENS

has been accepted towards fulﬁllment
of the requirements for the

 

 

MS. degree in Mechanical Engineering

eta/gs 9?;

Major Professor’s/Signature
7/22/04

Date

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6101 cJClRC/DatoDuopss-p. 15

iﬁm iﬁﬁ- _ __——- ——_———-

EFFECTS OF THREE-DIMENSIONAL GEOMETRY ON PENETRATION AND
PERFORATION RESISTANCE
By

George Joseph Coppens

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Mechanical Engineering

2004

ABSTRACT
EFFECTS OF THREE-DIMENSIONAL GEOMETRY ON PENETRATION AND
PERFORATION RESISTANCE
By
George Joseph Coppens
This thesis determined the penetration and perforation thresholds of laminated,

stitched, and two- and three-dimensionally woven composite plates subjected to
transverse impact. All composite plates were made from glass/epoxy prepreg tape so
direct comparisons could be made about the effects of through thickness reinforcement
on penetration and perforation thresholds. The effects of fiber angle were also studied.
The laminated plates were made with various stacking sequences and had no additional
through thickness reinforcement. The stitched plates were reinforced through the
thickness with one-millimeter wide strips of prepreg. The two- and three-dimensional
plates were hand woven using 12.7 mm wide strips of prepreg. The three-dimensional
weaving technique was innovative in that it incorporated new fabric geometry to
reinforce the plates through the thickness. A drop weight tester with an instrumented tup
was used to impact the plates. The impact test data was used to determine the penetration
and perforation thresholds. The three-dimensional woven plates had larger penetration
and perforation thresholds than the laminated and two-dimensional plates as well as
reduced delamination areas. The stitched plates had the largest penetration and
perforation thresholds. Through thickness reinforcement increased penetration and
perforation thresholds. The ﬁber angles of the laminated and three-dimensional plates

also inﬂuenced their penetration and perforation thresholds.

DEDICATION

This work is dedicated to all my family and friends who have supported me during the

years I have been in college.

iii

ACKNOWLEDGMENTS

The assistance of Dr. Dahsin Liu was gratefully appreciated during my time at MSU.

I would also like to thank my committee: Dr. Kwon, Dr. Lee, and Dr. Loos.

iv

TABLE OF CONTENTS

LIST OF TABLES ............................................................................................................ vii
LIST OF FIGURES ......................................................................................................... viii
l . Introduction ................................................................................................................. 1
1.1 Literature Survey ................................................................................................ 2
1.2 Scope of Current Study ....................................................................................... 4

1 .3 Organization ........................................................................................................ 5

2. Fabrication .................................................................................................................. 6
2.] Material ............................................................................................................... 6
2.2 Manufacturing ..................................................................................................... 6
2.2.1 Laminated Plates ......................................................................................... 6
2.2.2 Stitched Plate .............................................................................................. 8
2.2.3 Two-Dimensional Woven Plate .................................................................. 8
2.2.4 Three-Dimensional Woven Plates ............................................................ 1 1

2.3 Curing ............................................................................................................... 15
2.4 Speciﬁcations .................................................................................................... l 7

3. Testing ....................................................................................................................... 18
3.1 Testing Facility ................................................................................................. 18
3.2 Operating Procedures ........................................................................................ 20
3.3 Load-Deﬂection Curves .................................................................................... 21
3.4 Discussion ......................................................................................................... 23

4. Data Analysis ............................................................................................................ 24
4.1 Energy Proﬁle ................................................................................................... 24
4.2 Test Specimens ................................................................................................. 25
4.3 Frictional Effect ................................................................................................ 27
4.4 Measurement of Perforation Depth ................................................................... 29
4.5 Data Recording ................................................................................................. 31
4.6 Load-Deﬂection Curves for L[(O/9O)6] ............................................................. 32
4.7 Calculations of Energies ................................................................................... 33
4.8 Correction of Energy Calculations .................................................................... 35
4.8.1 Correction of Absorbed Energy ................................................................ 35
4.8.2 Correction of Impact Energy .................................................................... 37

4.9 Other Correction Methods ................................................................................ 39
4.9.1 Friction Removal Correction Method ....................................................... 39
4.9.2 Extended Method ...................................................................................... 42

5. Experimental Results and Discussions ..................................................................... 46
5.1 Load-Deﬂection Curves and Energy Proﬁles ................................................... 46
5.1.1 Laminated Specimens ............................................................................... 46
5.1.2 Stitched Specimens ................................................................................... 48
5.1.3 Two-Dimensional Woven Specimens ....................................................... 50

5.1.4 Three-Dimensional Woven Specimens ..................................................... 52

5.2 Discussions ....................................................................................................... 54
5.2.1 Angle Effect .............................................................................................. 54
5.2.2 Through-Thickness Effect ........................................................................ 56

5.3 Composite Damage ........................................................................................... 60

5.4 Material Behavior and Through-Thickness Reinforcement Hypotheses .......... 63

6. Conclusions and Future Study .................................................................................. 67
6. 1 Conclusions ....................................................................................................... 67
6.2 Future Study ...................................................................................................... 67

Appendices ........................................................................................................................ 70

Appendix A ....................................................................................................................... 71
Optical microscope images of cross sections of L[(0/90)(,], S[(0/90)6], 2D[(0/90)(,], and
3D[(O/90)(,] specimens taken at a magniﬁcation of 120x ............................................ 71

Appendix B ....................................................................................................................... 74
MATLAB program for calculating absorbed energy and impact energy ..................... 74

Appendix C ....................................................................................................................... 78
Load cell calibration data .............................................................................................. 78

Appendix D ....................................................................................................................... 80
Load-deﬂection curves and energy proﬁles of laminated specimens ........................... 80

Appendix E ....................................................................................................................... 89
Load-deﬂection curves and energy proﬁle of stitched specimens ................................ 89

Appendix F ........................................................................................................................ 92
Load-deﬂection curves and energy proﬁle of two-dimensional woven specimens ...... 92

Appendix G ....................................................................................................................... 95
Load-deﬂection curves and energy proﬁles of three-dimensional woven specimens .. 95

Appendix H ..................................................................................................................... 102
Laminated specimen damage ...................................................................................... 102

Appendix 1 ...................................................................................................................... 1 13
Stitched specimen damage .......................................................................................... 113

Appendix J ...................................................................................................................... l 16
Two-dimensional woven specimen damage ............................................................... l 16

Appendix K ..................................................................................................................... 1 l9
Three-dimensional woven specimen damage ............................................................. 1 19

References ....................................................................................................................... 128

vi

Table 2-1:

Table 4-1:

Table 4-2:

Table 4-3:

Table 4-4:

Table 5-l:

Table 5-2:

Table 5-3:

Table 5-4:

Table D-l:

Table D-2:

Table D-3:

Table 0-4:

Table 0-5:

Table E-l:

Table F-l:

Table 0-1:

Table 0-2:

Table G-3:

Table G-4:

LIST OF TABLES

Average thickness of composite plates. .................................................... 17
Results of friction effect tests. .................................................................. 28
Results of perforation depth tests .............................................................. 30
Results of ﬁiction removal correction method. ........................................ 42
Comparison of absorbed energy correction methods ................................ 44
L[(0/9O)6] specimens ................................................................................. 48
Stitched specimens. ................................................................................... 50
2D[(0/9O)6] specimens. ............................................................................. 52
3D[(O/9O)6] specimens. ............................................................................. 54
Data for L[(0/7.5)6] specimens. ................................................................ 82
Data for L[(0/15)6] specimens. ................................................................. 83
Data for L[(0/30)6] Specimens. ................................................................. 85
Data for L[(O/45)6] specimens. ................................................................. 86
Data for L[(0/90)6] specimens. ................................................................. 88
Data for S[(0/90)6] specimens. .................................................................. 91
Data for 2D[(0/90)6] specimens. ............................................................... 94
Data for 3D[(0/15)6] specimens. ............................................................... 97
Data for 3D[(O/30)6] specimens. ............................................................... 98
Data for 3D[(0/45)6] specimens. ............................................................. 100
Data for 3D[(0/90)6] specimens. ............................................................. 101

vii

Figure 2-1:
Figure 2-2:
Figure 2-3:
Figure 2-4:
Figure 2-5:
Figure 2-6:
Figure 2-7:
Figure 2-8:
Figure 2-9:
Figure 2-10:
Figure 2-1 1:
Figure 2-12:
Figure 3-1:
Figure 3-2:
Figure 3-3:
Figure 3-4:
Figure 4-1:
Figure 4-2:
Figure 4-3:
Figure 4-4:

Figure 4-5:

LIST OF FIGURES

Side view of laminated plate. ...................................................................... 7
Cutting pattern for 30° ply. ......................................................................... 7
Stitching pattern. Top view (a) and cross section (b). ................................ 8
Strips attached to stand. .............................................................................. 9
Heddles separating warp strips. ................................................................ 10
Side view of 2D geometry. ....................................................................... 1 1
3D geometry .............................................................................................. 11
Three-dimensional weave geometry in warp and fill directions ............... 12
Weaving instructions for one row of 3D geometry. ................................. 14
Step 3 of weaving 3D[(0/30)6] plate. ........................................................ 15
Vacuum bagging schematic. ..................................................................... 16
Autoclave set-up schematic. ..................................................................... 16
Schematic diagram of impact testing machine. ........................................ 18
Schematic diagram of rebound arrestor. ................................................... 19
Schematic diagram of specimen clamping ﬁxture. ................................... 19
- Specimen dimensions and unit cell. .......................................................... 20

Energy proﬁling method for determining penetration and perforation. 25

Load-deﬂection curves of test Specimens. ................................................ 26
Energy proﬁle of test specimens. .............................................................. 27
Load-deﬂection curves of lubrication test. ............................................... 28
Dimensions and notations for tup perforation tests. ................................. 30

viii

Figure 4-6: Load-deﬂection curves with and without foam. ....................................... 31
Figure 4-7: Load-deﬂection curves of L[(O/90)(,] specimens. ..................................... 32
Figure 4-8: Energy proﬁle of L[(0/90)6] specimens. ................................................... 34
Figure 4-9: Load and velocity curves of L[(0/90)6] specimen 8 .................................. 36
Figure 4-10: Corrected energy proﬁle of L[(0/90)6] specimens. ................................... 38
Figure 4-1 1: Tup measurements made for ﬁ'iction removal correction method. ........... 40
Figure 4-12: Removing friction distance of test specimen 6. ........................................ 40
Figure 4-13: Modiﬁed load-deﬂection curve of test Specimen 6 ................................... 41
Figure 4-14: Extended method for L[(O/90)6] specimen 4. ........................................... 43
Figure 4-15: Extended method for L[(0/90)(,] Specimen 8. ........................................... 43
Figure 5-1: Load-deﬂection curves of L[(0/90)6] specimens. ..................................... 46
Figure 5-2: Energy proﬁle of L[(0/90)6] specimens. ................................................... 47
Figure 5-3: Load-deﬂection curves of S[(0/9O)6] Specimens ....................................... 49
Figure 5-4: Energy proﬁle of S[(O/90)(,] Specimens. ................................................... 49
Figure 5-5: Load-deﬂection curves of 2D[(0/90)6] specimens. ................................... 51
Figure 5-6: Energy proﬁle of 2D[(0/9O)6] specimens .................................................. 51
Figure 5-7: Load-deﬂection curves of 3D[(0/9O)6] specimens. ................................... 53
Figure 5-8: Energy proﬁle of 3D[(0/90)6] specimens .................................................. 53
Figure 5-9: Impact energy interval of laminated Specimens ........................................ 56
Figure 5-10: Impact energy interval of 3D specimens. ................................................. 56
Figure 5-11: Impact energy interval of [(0/90)(,] specimens .......................................... 58
Figure 5-12: Impact energy interval of specimens with equal 0 ....................................... 58
Figure 5-13: Delamination of L[(0/45)6] and 3D[(0/45)6] specimens. .......................... 60

ix

Figure 5-14:
Figure 5-15:
Figure 5-16:
Figure 5-17:
Figure 6-1:
Figure A-l:
Figure A-2:
Figure A-3:
Figure A-4:
Figure C-l:
Figure D-l:
Figure D-2:
Figure D-3:
Figure D-4:
Figure D-5:
Figure D-6:
Figure D-7:
Figure D-8:
Figure D-9:
Figure D-lO:
Figure E-l:
Figure E-2:

Figure F-l:

Delamination of 2D[(0/90)(,] and 3D[(0/90)6] specimens ......................... 60
Top view of damage to 3D[(0/45)6] specimens. ....................................... 62
Bottom view of damage to 3D[(O/45)6] specimens ................................... 63
Normalized DH and D16 values for two-ply laminate. .............................. 65
Proposed tup design. ................................................................................. 69
Cross section of L[(0/90)6] specimen. ...................................................... 72
Cross section of S[(0/90)6] specimen ........................................................ 72
Cross section of 2D[(0/90)6] specimen. .................................................... 73
Cross section of 3D[(0/90)6] Specimen. .................................................... 73
Load-cell calibration data ......................................................................... 79
Load-deﬂection curves of L[(O/7.5)6] specimens. .................................... 81
Energy proﬁle of L[(0/7.5)6] specimens. .................................................. 81
Load-deﬂection curves of L[(O/15)6] specimens. ..................................... 82
Energy proﬁle of L[(0/15)(,] specimens. ................................................... 83
Load-deﬂection curves of L[(0/30)6] specimens. ..................................... 84
Energy proﬁle of L[(0/30)6] specimens. ................................................... 84
Load-deﬂection curves of L[(0/45)6] specimens. ..................................... 85
Energy proﬁle of L[(O/45)6] specimens. ................................................... 86
Load-deﬂection curves of L[(O/90)6] specimens. ..................................... 87
Energy proﬁle of L[(0/9O)6] specimens. .................................................. 87
Load-deﬂection curves of S[(0/90)6] specimens ....................................... 90
Energy proﬁle of S[(O/90)6] specimens. ................................................... 9O
Load-deﬂection curves of 2D[(0/9O)6] specimens. ................................... 93

Figure F-2:
Figure G-l:
Figure 0-2:
Figure G-3:
Figure 0-4:
Figure G-S:
Figure G-6:
Figure 0-7:
Figure 0-8:
Figure H-l:
Figure H-2:
Figure H-3:
Figure H-4:
Figure H-S:
Figure H-6:
Figure H-7:
Figure H-8:
Figure H-9:

Figure H-IO:

Figure l-l:
Figure 1-2:
Figure J-l:

Figure J-2:

Energy proﬁle of 2D[(O/90)6] specimens .................................................. 93
Load-deﬂection curves of 3D[(0/ l 5)6] specimens. ................................... 96
Energy proﬁle of 3D[(O/1 5)6] specimens .................................................. 96
Load-deﬂection curves of 3D[(0/30)6] Specimens. ................................... 97
Energy proﬁle of 3D[(O/30)6] specimens .................................................. 98
Load-deﬂection curves of 3D[(0/45)6] Specimens. ................................... 99
Energy proﬁle of 3D[(0/45)6] Specimens .................................................. 99
Load-deﬂection curves of 3D[(0/9O)6] specimens. ................................. 100
Energy proﬁle of 3D[(O/90)6] specimens ................................................ 101
Top view of damage to L[(0/7.5)6] specimens ........................................ 103
Bottom view of damage to L[(0/7.5)(,] specimens. ................................. 104
Top view of damage to L[(O/15)6] specimens ......................................... 105
Bottom view of damage to L[(O/15)6] Specimens. .................................. 106
Top view of damage to L[(O/30)6] specimens ......................................... 107
Bottom view of damage to L[(0/30)6] specimens. .................................. 108
Top view of damage to L[(O/45)(,] Specimens ......................................... 109
Bottom view of damage to L[(0/45)(,] specimens. .................................. 1 10
Top view of damage to L[(0/90)6] specimens ......................................... 1 1 1
Bottom view of damage to L[(0/90)6] specimens. ................................. l 12
Top view of damage to S[(0/90)6] specimens. ........................................ 1 14
Bottom view of damage to S[(0/90)6] Specimens. .................................. 1 15
Top view of damage to 2D[(O/90)6] Specimens. ..................................... 117
Bottom view of damage to 2D[(0/90)6] specimens ................................. 1 18

xi

Figure K-l:
Figure K-2:
Figure K-3:
Figure K-4:
Figure K-S:
Figure K-6:
Figure K-7:

Figure K-8:

Top view of damage to 3D[(0/15)6] specimens. ..................................... 120

Bottom view of damage to 3D[(O/15)6] Specimens ................................. 121
Top view of damage to 3D[(O/3O)6] specimens. ..................................... 122
Bottom view of damage to 3D[(O/30)6] specimens. ............................... 123
Top view of damage to 3D[(0/45)6] specimens. .................................... 124
Bottom view of damage to 3D[(0/45)6] specimens. ............................... 125
Top view of damage to 3D[(0/90)6] Specimens. .................................... 126
Bottom view of damage to 3D[(O/9O)6] specimens. ............................... 127

xii

1. Introduction

Composite materials offer high strength-to-weight and stiffness-to-weight ratios
making them excellent candidates for use in structures where strength must be maximized
while minimizing weight such as high performance cars and racing boats. Composites
can also be used as armor for civilian and vehicle applications due to their high energy
absorption capabilities. Their role is to provide penetration resistance, impact energy
dissipation, and damage containment [1]. Material selection of ﬁbers and matrix,
stacking sequence, and translaminar reinforcing techniques are some of the factors taken
into account when designing composite armor.

Composite materials offer many beneﬁts when compared to conventional metals.
Composites can behave very poorly when subjected to transverse loading. One of the
worst behaviors of composites is their tendency to delaminate when loaded transversely.
Delamination can cause severe reductions in in-plane strength and stiffness, which can
lead to failure of an entire structure. This drawback may be one of the biggest limiting
factors on composite materials being used in more areas [2]. Other forms of damage are
matrix cracking, ﬁber-matrix debonding, ﬁber microbuckling, ﬁber shear-out, and ﬁber
fracture [3, 4].

Composite materials need to be more resistant to transverse loading. The amount of
energy that composites can resist before penetration and perforation is reduced by
delamination [5]. The motivation of this work was to increase penetration and
perforation resistance by reducing delamination. There are two primary ways to achieve

this goal; one is to use through thickness stitching and the other is to use woven fabrics.

1.1 Literature Survey

Laminated composite plates made from unidirectional ﬁbers are susceptible to low
velocity impact loads. Transverse damage resistance is especially poor since laminated
composites have no through-thickness reinforcement; There have been many studies on
laminated composites subjected to low velocity impact as evidenced by the review of
Richardson and Wisheart [6]. Most studies agree that the most detrimental damage in
composite laminates subjected to impact loading is delamination [2,7]. This type of
damage can occur by relatively light impacts while the surface appears to be undamaged
[8]. Laminated panels are still attractive because there are no crimp angles to reduce the
in-plane properties and ﬁber volume fractions.

Many methods have been investigated with the goal of increasing the interlaminar
fracture toughness of laminated composites. These include using toughened
Ithermosetting matrices, translaminar reinforcement in the form of stitching, z-pinning,
knitting, braiding, weaving, and modifying interfacial properties. Some studies have
shown stitching can increase compression after impact strengths by 50% and increase
Mode I ﬁacture toughness by a factor of 30 [9]. Larsson found that stitching could
increase impact delamination energy by more than 20 times when compared to unstitched
plates [10]. This is because the stitching improves the delamination resistance energy by
raising the Mode I interlaminar ﬁacture resistance of the laminate, which makes it more
difﬁcultfor a delamination crack to propagate between the ﬁber plies [1 1].

Stitching clearly has many beneﬁts, including improved impact damage tolerance and

improved delamination resistance to ballistic impact. However, there are problems

associated with stitched composites. These include difﬁculties in stitching complex

shapes along with size and thickness restraints imposed by the sewing machines. Large
purpose-built sewing machines require extremely high capital costs that are usually
beyond the budget of most composite fabricators [12].

Stitching can also decrease in-plane stiffness and tensile and compressive properties
by varying amounts [13]. The thread and needle used for stitching can damage the
microstructure by breaking, spreading, and crimping the ﬁbers around the stitch holes.
Resin rich regions form around the stitch holes causing possible stress concentration
zones[ll]

Composite plates made from laminated two-dimensional (ZD) woven fabric have
received much attention. 2D fabric consists of plain, satin, twill, etc. weaving
geometries. 2D fabrics offer improved impact resistance and damage tolerance because
of their integrated nature and balanced in-plane properties [14]. Woven fabric laminates
have been shown to have Mode I interlaminar ﬁ'acture toughness of four to ﬁve times
greater than laminates made of unidirectional fabric. This can be attributed to the
roughness of the fabric, resin rich regions between the plies, and the ways in which crack

propagation occurs [2]. The resin rich areas tend to arrest the interplay cracks and cause
them to “jump” between undulations rather than extend continuously. The cracks also
have difﬁculty in propagating because of the undulating paths that occur in the fabric
[15]. Woven fabrics also have smaller damage areas after impact, thus they have higher
residual compression strength when compared to unidirectional laminates. These
strengths can be attributed to the more ductile and compliant nature of woven fabrics [2].
Siow and Shim studied plain weave carbon epoxy plates with a laminate sequence of

[0/90/-45/45/0/90]s- They found the damage mechanisms for woven laminates to be

mainly delamination and ﬁber breakage which were Similar to unidirectional laminates
[16].

Three-dimensional (3D) composites have become very popular based on their greater
delamination resistance, ballistic damage resistance, and impact damage tolerance.
Weaving, braiding, stitching, and knitting are all methods for producing 3D composites.
The impact energy needed to initiate damage in 3D woven carbon-bismaleimide
composites is up to 60% higher than in a laminated counterpart of the same materials.
Their Mode I interlaminar ﬁacture toughness values can be 6-20 times higher than
unidirectional composites. This group of composites gets their superior properties from
the through-thickness binder yarns which can arrest or slow the growth of delamination
cracks [12].

Many of the in-plane properties of 3D composites are usually inferior to laminated
counterparts when an equivalent amount of ﬁbers are aligned in the load direction.
Stiffness values are similar to 2D fabrics but their tension and compression strengths may
be lower by 15-20%. The strength reduction is due to the crimping and distortion of in-
plane ﬁbers by the binder yarns [12].

1.2 Scope of Current Study

This thesis research attempted to determine the energy required to cause penetration
and perforation of glass/epoxy composite plates subjected to low velocity impact. The
use of only one material allowed direct correlations to be made between fabric geometry
and penetration and perforation resistance.

I Laminated, stitched, 2D woven, and 3D woven geometries were tested. The laminated

geometry was used to produce a baseline for comparing the other geometries to. The

laminated plates had no through-thickness reinforcement. The stitched plates were
reinforced through the thickness by thread. Each piece of glass/epoxy that made up the
2D woven plate was reinforced, but the pieces were only joined by matrix material. The
3D woven geometry used the ﬁbers, as well a matrix, to join all of the plies together
through the thickness.
1.3 Organization

This thesis is divided into Six chapters. Chapter 1 introduces composite materials
along with their advantages and drawbacks. The reasons for conducting this study are
discussed. Chapter 1 also provides a literature survey of recent work performed on
laminated, stitched, 2D woven and 3D woven composite materials. Chapter 2 discusses
the materials and methods used for fabricating the composite plates. The procedure used
to cure the plates is included along with the speciﬁcations of the composite plates.
Chapter 3 includes the equipment and procedures used to test the composite plates and
the equations used to calculate their performance. Chapter 4 discusses the energy proﬁle
method used to determine the penetration and perforation resistance of the composite
plates. The problems encountered while testing along with their solutions are presented.
The results of laminated specimens are used to discuss the problem solutions. Chapter 5
presents selected results from this study along with discussions on angle effect and the
effects of through-thickness reinforcement. Chapter 6 concludes the entire project and

offers recommendations for future studies.

2. Fabrication

The following sections discuss the material and methods used to construct the
composite plates. The autoclave cure cycle for the thermosetting composite material is
also presented.
2.] Material

All composite plates constructed for this study were made from Scotchply type 1003-
A tape which was a non-woven, unidirectional ﬁberglass tape pre-impregnated (prepreg)
with an epoxy matrix. The prepreg tape came on a 300 mm (12”) wide roll with a total
length of 66 m (72 yards). The prepreg tape was sealed inside a plastic bag and stored in
a freezer when not being used. The sealed plastic bag containing the prepreg tape was
removed from the freezer and allowed to warm for approximately one hour prior to use.
Leaving the prepreg tape in the sealed plastic bag while warming prevented condensation
from forming on the composite material.
2.2 Manufacturing
2.2.1 Laminated Plates

Laminated composite plates were constructed from twelve pieces of prepreg tape.
Each piece was 300 mm x 300 mm, namely 0° and 90° ply. The angled plies were cut by
using patterns. The patterns were placed on the prepreg tape and then cut around. The
plies were then stacked together to create the laminated plates, as shown in Figure 2-1.
An optical microscope image of the actual cross section of a portion of a L[(0/90)(,]
specimen at a magniﬁcation of 120X is shown in Appendix A. The plates had a stacking

sequence of [0/0/0/0/0/0/0/0/0/0/0/0] with 0 being equal to 7.5, 15, 30, 45, or 90 degrees.

They were designated as L[(0/0)6]. The plates were unsymmetric and had dimensions of

300 mm x 300 mm.

 

Figure 2-1:Side view of laminated plate.

Special tailoring was required for the angled plies where 0 equaled 7.5, 15, 30, or 45
degrees. Gaps were created in the angled plies since the tape was only 300 mm wide.
Figure 2-2 illustrates how the prepreg tape was cut to create the pieces labeled A and C.
The horizontal lines were used to represent the direction of the ﬁbers. The area enclosed
by the dashed lines, labeled A’, was the gap. Piece A was used to ﬁll the gap to create
the 300 mm x 300 mm angled ply. The length of each ply and the cutting lines were
determined in the CAD program that was used to create the patterns. The ﬁber continuity
was important when creating the angled plies. Only certain pieces of the pattern could be

used to ﬁll gaps. Area B could have been rotated 90° clockwise and used to ﬁll gap A’

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

i: 420 mm =i
1r— """ ‘Lx' ———————
l.— B l/ \\\ A J77]!
Lﬂf \\/’ |
: \ :
300 mm | [F \j
: [z c J/ :
l / / l
. / /
.[ j/ .
_v__ l:\_\_ ___________ 7L- J
\\\ \\ A, ,’I

Figure 2-2:Cutting pattern for 30° ply.

but the ﬁber orientation would have been wrong. In addition, the plies were cut so that
edges of all gaps were parallel to the ﬁber direction.
2. 2.2 Stitched Plate

The stitched plate was based on a laminated stacking sequence of L[(0/90)¢,] which
was unsymmetric. The stitching was done by hand using a needle and 1 mm wide strips
of prepreg for thread. A horizontal stitching pattern was used as shown in Figure 2-3 a.
The nodes in the ﬁgure represent the stitching points for a portion of the plate. The solid
and dashed lines represent the thread above and below the plate, respectively. The path
of the thread through the plate is shown in Figure 2-3b. An optical microscope image of
the actual cross section of a portion of a S[(0/90)6] specimen at a magniﬁcation of 120x
is shown in Appendix A. The distance between each stitch as well as each row of
stitching was 12.7 mm forming unit cells of 12.7 mm x 12.7 mm. The stitched plate was

designated as S[(0/90)6] and had dimensions of 300 mm x 300 mm.

W M “~_.A"\ —f""-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

12.7
mm
‘ A’ 12.7
mm
L/\/\tJ\/—\.
“ J ‘ J/“N
(a) (b)

Figure 2-3:Stitching pattern. Top view (a) and cross section (b).

2.2.3 T wo-Dimensional Woven Plate
The two-dimensional (2D) woven plate consisted of six pieces of plain weave prepreg

that were stacked together. Each piece was very similar to a layer of conventional woven

fabric composite. However, the plies were manufactured from the prepreg tape rather
than from a prefabricated woven fabric. Each of the 2D woven pieces had to be woven
by hand using a fabricated loom. This process began by cutting the prepreg tape into 458
mm x 12.7 mm strips. The ﬁber direction was parallel to the cutting direction. The ends
of the strips were placed side by side on a warp board, paper backing up, and then
secured to the board by masking tape. This procedure was repeated for the other end of
the strips, except that a 25 mm length of the paper backing was removed from the end of
each strip before taping. Each piece consisted of 26 warp strips. Leaving the paper
backing on the strips until it was required to be removed prevented the ﬁbers from getting

damaged during the weaving process.

Support bar

  
  

Warp boards
C-clamp

Warp strips

Figure 2-4:Strips attached to stand.

The strips and boards were then attached to a fabricated stand, paper backing down,
with c-clamps as shown in Figure 2-4. The warp boards were placed 380 mm apart
which created slack in the strips so that they could be moved in the vertical direction
when inserting the ﬁll strips. Heddles were fabricated by bending 18 gauge steel wire

into the required shape. The heddles were designed so that the warp strips could be

inserted through them aﬁer they were ﬁxed at both ends. Two heddle bars, each with
thirteen heddles, were used to weave the prepreg strips. The heddles Were used to
separate the warp strips so that the ﬁll strips could be inserted as shown in Figures 2-5a
and 2-5b. One set of heddles would pull up on the even numbered strips while the other
set would push down on the odd numbered strips as shown in Figure 2-Sa. The heddle
bar positions were reversed prior to the next ﬁll strip insertion as shown in Figure 2-5b.
The heddle bar in the up position would be clamped to the support bar during ﬁll strip
insertion. The weight of the heddle bar in the down position was sufﬁcient to hold the
strips in their required position. Approximately 25 mm of paper backing was removed

from each warp strip prior to the placement of each ﬁll strip.

 

Figure 2-5: Heddles separating warp strips.

The process of switching the heddles, removing paper backing, and placing ﬁll strips
was repeated until each piece was completed. Six pieces were individually woven in
total and stacked together with both warp and ﬁll units well aligned through the
thickness. The 2D woven plates with the geometry shown in Figure 2-6 were designated

as 2D[(0/90)6], where the underline emphasized woven. The panels had dimensions of

 

 

 

 

 

 

 

 

 

 

 

 

\ /
\ J \ / > One piece
Ply 6 \ I \ / Warp ply
\ / \ I ~ Fill ply
Ply 12 g \ I \ J

Figure 2-6:Side view of 2D geometry.

300 mm x 300 mm after removing the excessive warp and ﬁll units from all edges.
Though not exact, the 2D woven composite plate was close to being symmetric about its
midplane. An optical microscope image of the cross section of a portion of a 2D[(Q/9_0)6]
specimen at a magniﬁcation of 120X is shown in Appendix A.
2.2.4 Three-Dimensional Woven Plates

The three-dimensional (3 D) woven plates used a novel manufacturing technique to
create a geometry in which 12.7 mm wide strips of prepreg were interwoven in the warp,

ﬁll, and through thickness directions as shown in Figure 2-7.

 

Figure 2-7:3D geometry.

The geometry was similar to the 2D woven plate; however, each ply of the 3D plate
was interwoven with the others. The 2D plate consisted of Six pieces of plain-woven
prepreg that were joined by the epoxy matrix between them. Figure 2-6 shows that in the

2D plate plies l and 2, 3 and 4, 5 and 6, 7 and 8, 9 and 10, and 11 and 12 were woven

ll

together. The 3D plate differs because in the warp direction plies 1 and 2, 2 and 4, 4 and
6, 6 and 8, 8 and 10, and 10 and 12 were interwoven together as shown if Figures 2-7 and
2-8a. Plies 1 and 3, 3 and 5, 5 and 7, 7 and 9, 9 and 11, and 11 and 12 were interwoven
in the ﬁll direction as shown in Figures 2-7 and 2-8b. This 3D geometry created a plate
with the same thickness as the 2D plate but without having only the epoxy matrix to

connect each layer.

Fly]

3'

Warp ply

Pl 6
y Fill ply

ii

 

‘ Ply 12
(a) warp direction

 

 

Plyl

 

5i

=*Warp Ply

Pl 6
y Fill ply

P1y12-=-

(b) ﬁll direction
Figure 2-8:Three-dimensional weave geometry in warp
and fill directions.

The procedure for creating the 3D woven plate was extremely time consuming and
labor intensive. This geometry required that each ﬁll row be completed before the next
could begin. No automation was incorporated into weaving the plates as no equipment
could be found that could create the 3D geometry, thus all weaving was done by hand.
All warp strips of the ﬁrst ply had to be taped, paper backing side up, to a warp board
only at one end before weaving could begin. A section of the paper backing was

removed from the end of each strip where the tape was placed. The next ply of strips

12

then had to be placed directly over the previous ply, paper backing removed, and taped to
the warp board. This procedure was repeated until all strips of six plies were taped to the
warp board. The other ends of the strips were not taped as in the two-dimensional
weaving. The fabricated plates consisted of twenty-six strips per ply with the panel
having six plies in the warp direction and six plies in the ﬁll direction.

The warp board and strips were secured to an elevated work surface with the paper
backing down. Non-perforated Teﬂon fabric was used to prevent the strips from sticking
to the work surface. The 3D weaving process required that warp strips and associated
paper backing be folded back in the sequence presented in Figure 2-9. The paper backing
remained on the warp strips until they were folded back. The length of paper backing
removed depended on the ﬁll angle, but enough length had to be removed so that none
remained between the warp strips and ﬁll strips during the weaving of each row. Figure
2-10 shows step 3 prior to placing a ﬁll strip over the warp strips for the 3D[(9_/9_0)6]
plate. The ﬁll strips are folded back and the paper backing has been trimmed.

3D woven plates had orthogonal as well as non-orthogonal angles between warp and
ﬁll strips. The ﬁll strips were placed at angles of 15, 30, 45, and 90 degrees from the
warp strip direction. These plates were designated as 3D[(m)6], 3D[(Q/ﬂ)6],
3D[(O_/ﬁ)(,], and 3D[((_)19_0)6]. The plates had dimensions of 300 mm x 300 mm aﬁer the
edges were trimmed. An optical microscope image of the cross section of a portion of a
3D[(M)6] specimen at a magniﬁcation of 120x is shown in Appendix A.

The procedure for weaving the next ﬁll row followed the same steps. However, the
warp strips that were folded back and then placed over the ﬁll strips would change. For

example, in step one, the warp strips in rows 1, 3, and 5 would be folded back and all but

13

one strip in rows 2 and 4 would be folded back. The completed second ﬁll row should
look like that given in Step 8 of Figure 2-9. The remaining odd ﬁll rows should be the
same as the ﬁrst ﬁll row while the remaining even ﬁll rows will be the same as the

second ﬁll row.

 

E :1

1 2 3 4 5
Step 1. Fold back all warp strips in
rows 2 and 4. Fold back all but one
strip in rows 1, 3, and 5.

:2

W

Step 2. Place a fill strip over warp
strips 1, 3, and 5.

 

 

 

 

W

Step 3. Place another warp strip over
the ﬁrst fill strip in rows 1, 3, and 5.
Place another ﬁll strip over the warp
strips.

 

 

 

 

 

 

Step 4. Place warps strips in every row
over the last fill strip. Add another ﬁll
strip.

 

 

 

 

 

Step 5. Place warp strips in every row
over the last fill strip. Add another fill
strip.

 

 

 

Step 6. Place warp strips in every row
over the last fill strip. Add another fill

 

 

 

Step 7. Place warp strips in every row
over the last fill strip. Add the ﬁnal
fill strip. Then place two warp strips
in rows 2 and 4 to complete the row.

 

 

 

 

 

Step 8. Repeat steps 1-7 for the second
fill row and each successive fill row
until all 26 till rows are completed.
Steps 1-7 only Show 5 out of 26 warp
rows.

 

Figure 2-9:Weaving instructions for one row of 3D geometry.

l4

 

Paper backing
on ﬁll strips

 

Figure 2-10: Step 3 of weaving 3Dlw6] plate.

2.3 Curing

The composite plates were cured in an autoclave. Six panels were cured at a time to
ensure that they all received the same cure cycle. The following cure cycle was used:

1. Set pressure in autoclave to 560 kPa.

2. Ramp temperature from room temperature to 160° C at ten degrees per minute.

3. Hold temperature at 160° C and pressure at 560 kPa for 45 minutes.

4. Cool ﬁ'om 160° C to room temperature at 10° per minute then release pressure.

Vacuum bags were used during the cure cycle along with a vacuum pump to remove
air bubbles that formed during curing. The vacuum hoses were attached to vac valves
that allowed gases to be removed from the vacuum bags while maintaining negative
pressure in the vacuum bags. The vacuum Was maintained at 13 inches of mercury (44
kPa) from the beginning of the cure cycle until ﬁve minutes into step 3 at which time the
vacuum was vented to the atmosphere. Porous Teﬂon and bleeder fabric was placed on
the tops and bottoms of the composite plates as shown in Figure 2-1 1. Vacuum bags,
which were used to contain the composite plates, porous Teﬂon, and bleeder fabric, were

then placed on top of aluminum caul plates. Only one caul plate was used, i.e. the

vacuum bag was not sandwiched between two aluminum plates as in conventional
autoclave procedures. This allowed composite plates freedom to warp which was caused

by their unsymmetric stacking sequences.

Vacuum —_,

 

   
  

 

 

 

 

line ﬁ'om

vac valve —————————— 3__ goaous
e on

wens; *—-—-— Bleeder

Tacky tape __________ \ (2 plies)
Composite 7;" ' I "i >Porous
plate Teﬂon

Caul plate

 

Figure 2-11: Vacuum bagging schematic.

The vacuum line into the autoclave was Split into three lines using a manifold
constructed of brass tubing and “T” ﬁttings. Each vacuum bag contained two composite
plates and one vac valve. The three vacuum lines were attached to the three vac valves.
The vacuum bags were separated in the autoclave by fabricated steel stand-offs as Shown

in Figure 2-12. The middle and upper caul plates and the specimens were not shown.

Thermocouple

  
  
  
  
  
  

Autoclave walls
Vac valve

Vacuum lines

Stand-offs
Lower caul plate

Figure 2-12: Autoclave set-up schematic.

l6

2.4 Specifications

All of the composite plates warped slightly at their corners. This was partially caused
by the asymmetry of the plates. The vacuum bags also caused some of the warping. The
bags would distort when air was removed from them. The composite plates would
conform to the shape of the vacuum bags and cure with the distorted Shape. The
L[(O/7.5)6] plate was also slightly deformed by the vac valve during the cure cycle by
conforming to the pattern on the bottom of the vac valve. The curved comers of the
specimens were removed by a belt sander.

The thickness of each specimen was measured and the average values were recorded
in Table 2-1. All specimens had similar thicknesses, as they were all 12 plies thick. The
woven specimens were approximately 0.1 mm thicker because of the resin pockets due to

the geometry.

Table 2-1: Averagethickness of composite plates.

 

 

 

 

 

 

 

 

 

 

 

 

17

Type L[(O/7.5)6]| L[(0/15)6] L[(0/30)6] L[(O/45)6] L[(O/90)6] S[(O/90)6]]
Thickness (mm) 2.6 | 2.6 2.6 2.6 2.6 2.6 |
Type 20[(g/2<2>61130[(o_/1_6)61 mug/20).] mama] 30mm»):
Thickness (mm 2.7 2.7 2.7 2.7 2.7

3. Testing
3.1 Testing Facility

The composite plates were tested with an instrumented drop-weight impact tester.
Each 300 mm x 300 mm plate was cut into nine 100 mm x 100 mm Specimens with a
diamond blade circular saw. The drop weight tester consisted of the items labeled in
Figure 3-1. The hemispheric nose, 12.7 mm diameter tup was connected to a 22,241 N
load cell that was attached to the crosshead. The tup had an overall length of 50.8 mm
and a mass of 92.4 g. The crosshead was secured to the height adjustment clamp by a
latch. The crosshead and height adjustment clamp could slide with negligible friction
along the guide rails. The total weight of the crosshead, load cell, and tup was 49.3 N,

which corresponded to a mass of 5.03 kg.

   

Height
T0p\ as ~—adjustment
surface \ﬁ-<—— Latch clamp

Crosshead

 

Load cell
Bottom / Tup
surface

 

 

Guide rail—>

je— Roller lever

switch

 

 

< Guide rail

 

 

 

 

 

 

 

 

Figure 3-1:Schematic diagram of impact testing machine.

18

The rebound arrestor consisted of a pneumatic air cylinder, a solenoid valve, relay, a
toggle switch, and a roller lever switch as shown in Figures 3-2 and 3-3. The switches
were held in place by a stand not shown in the ﬁgures. The top and bottom plates of the
specimen clamping ﬁxture had cutouts of 76 mm x 76 mm. Four toggle clamps, shown
in Figure 3-3, were used to secure the top plate and the specimen to the bottom plate.
Toggle clamps were used to ensure that the clamping points and clamping forces were
consistent for all types of specimens tested. Clamping resulted in a ﬁxed boundary

condition Simulating that the specimens were small sections of large structures.

 
  
 

Roller lever —>f,.
switch ..
TOggle switch #133. J
Relay —>:‘ .

 

 

 

 

 

§‘—Air cylinder 2 Power

Solenoid —~ ;':::‘-—Air in

 

.54.}.

 

Figure 3-2:Schematic diagram of rebound
arrestor.

   

Toggle clamps

  
 

76 mm x 76 mm

Figure 3-3:Schematic diagram of specimen clamping
ﬁxture.

3.2 Operating Procedures

Each test consisted of placing a 100 mm x 100 mm specimen on the bottom plate of
the clamping ﬁxture. The top plate was then placed over the specimen and secured with
the toggle clamps. The crosshead was then raised to a desired height above the specimen
by adjusting the position of the height adjustment clamp. Finally, the latch was pressed
to release the crosshead. The crosshead would drop under the force of gravity and be
guided by the rails. The tup would strike the Specimens at their centers. The centers of
the stitched and woven composites were carefully adjusted to be the centers of their unit

cells, shown in Figure 3-4. This resulted in the best condition for impact.

100mm———’|

    

100 mm Unit cell

 

J;
Figure 3-4:Specimen dimensions and unit cell.

A photogate system consisting of the two ﬂags and an infrared emitter/detector was
used to determine the impact velocity, Vi- The signal normally read by the computer was
zero volts. The ﬂags, shown in Figure 3-1, would produce two ﬁve-volt spikes in the
signal as they passed through the emitter/detector. Each ﬂag would produce its own
individual Spike. The data acquisition software would then measure the time between the

two spikes. This time, t, and the distance, d (10.3 mm), between the two ﬂags could be

20

used to determine the impact velocity, i.e. v,- = d / t. Both ﬂags needed to be just below

the emitter/detector when the tup made contact with the specimens for the computer to be
triggered correctly.

The crosshead would move past the roller lever switch then the bottom surface of the
crosshead would move the toggle switch to the “on” position while dropping by striking
the toggle. This would cause power to be sent to the roller lever switch. In the event of
the tup rebounding, the roller lever switch would be hit by the top surface of the
crosshead. Since the roller lever switch would have power when the crosshead hit it the
second time, the relay would latch and open the solenoid valve causing the air cylinder to
extend thus preventing the tup from hitting the specimen a second time. The toggle
switch was positioned so that it would be turned “on” just as the tup made contact with
the specimens. The roller lever switch was located 270 mm above the toggle switch for
all tests. The load on the tup during impact was recorded by a computer and subsequent
data analysis was performed by a computer program.

3.3 Load-Deﬂection Curves

The composite specimens were tested by adjusting the drop height while keeping the
crosshead weight constant. Tup load, F (t), was recorded at a sampling rate of 25 us which
was used to calculate the acceleration, a(t), after dividing by the combined mass, m, of
the crosshead, load cell, and tup, i.e.

a(t) = F(t)/m. (3.1)
Throughout this thesis, m was equal to 5.03 kg for all tests. The computer would record
2048 data points during each test resulting in the maximum capability of recording an

impact event of 50 ms. This duration was sufﬁcient for all of the impact tests performed

21

in this thesis. The velocity, v(t), at each time step was calculated by integrating the
acceleration, a(t), using Equation (3.2) where 0 corresponded to the time when the

computer began recording load data, t was the duration of the event, and v,- was the

impact velocity measured by the photogate system.

t
v(t) = - [a(ma + v,- (3.2)
o

The deﬂection history, (5(t), was calculated by integrating the velocity history using
Equation (3.3).

t
a(z) = Iv(t)dt (3.3)
0

Since both load and deﬂection could be expressed as functions of time, the direct relation
between load and deﬂection, i.e. the load deﬂection relation

F = f (6 ) (3.4)
could be established. The load-deﬂection curve was then used to determine the absorbed

energy, Ea , using Equation (3.5) where 6, was the deﬂection when the force became

zero again at the end of impact.

5r
Ea = [new (3.5)
o

A program was written in MATLAB to perform the calculations listed in the above

equations and is included in Appendix B.

22

3.4 Discussion

The tup was made of high carbon steel and subjected to heat treatment. It was
assumed to be perfectly rigid for all tests conducted. The load applied to the tup was
transferred to the load cell that was not perfectly rigid. The load cell would deform and
the deformation would be measured by four strain gages attached to the load cell. The
purpose of using four strain gages on a square load cell was to compensate for the effect
due to bending. The strain measurement would then be multiplied by a calibration factor
of 3326 to calculate the load. The calibration factor was determined by calibrating the
load cell using quasi-static compression. The calibration curve for the 22,241 N load cell
is shown in Appendix C. The assumption of perfect rigidity and the mass (92.4 g) of the
tup in front of the load cell, along with the accuracy of the calibration factor, could cause
some errors to the measurement of the tup load, F (t). These errors Should be included in

the ultimate analysis of experimental accuracy.

23

4. Data Analysis
4.1 Energy Proﬁle

The objective of this thesis research was to determine the energy levels required to
cause penetration and perforation of composite plates, the so-called penetration and
perforation thresholds. A method based on impact and absorbed energies was used for
determining the thresholds [17]. This method was called the energy proﬁling method. A
sketch of a typical energy proﬁle for specimens subjected to central impact is given in
Figure 4-1. The solid circles resemble experimental results. They are based on the

energy delivered to the specimens, i.e. the impact energy, E ,- , and the energy absorbed by
the Specimens, i.e. the absorbed energy, Ea . The impact energy values included both

kinetic energy and potential energy. The absorbed energy values assumed all forms of
energy absorption, such as elastic and plastic deformation, fracture, and friction. There
was also energy absorbed by the testing facility in terms of vibration and heat. Hence,
the absorbed energy values were usually less than their respective impact energies for
specimens subjected to central impact.

Figure 4-1 shows that the absorbed energy increases as the impact energy increases.
There comes a point where the impact energy and the absorbed energy ﬁrst become equal
to each other. This point is called the penetration point and the corresponding energy
value, the penetration threshold. AS the impact energy further increases, the impact and
the absorbed energies remain equal to each other, namely, the equal energy interval. It is
also called the penetration process zone. There comes another point just before the
impact energy becomes greater than the absorbed energy again. This point is called the

perforation point and the corresponding energy value, the perforation threshold.

24

25

 

 

 

 

Perforation

20 - Equal energy 3 g
:- W[
> .
g 15 ~ Equal energy line Penetration
if: e
u 10 a
o
E O
8 5 - .
2 o

0 1 t I F l

0 5 1O 15 20 25
Impact Energy, J

Figure 4-1:Energy proﬁling method for determining
penetration and perforation.

4.2 Test Specimens

The ﬁrst group of tests conducted was on a polymeric material reinforced with short
glass ﬁbers in random orientations. The specimens were impacted and the energy proﬁle
was established. This study was performed so that the user could become familiar with
the instrumented drop-weight impact tester, rebound arrestor, data acquisition, data
processing, and the energy proﬁle method. It was also performed to establish the
protocols of experiment and data analysis that would be used later for the glass/epoxy
composite plates.

The load-deﬂection curves of the test Specimens are shown in Figure 4-2. The curves
were established from data calculated by the software prepared by the manufacturer of
the instrumented drop-weight impact tester. Figure 4-2 shows that the specimens tested
produced open and closed curves. It is also noted from the ﬁgure that the eleven curves
overlap well in both the loading and unloading sections although the discrepancy on the

peak load seems to be signiﬁcant. The closed curves, numbered 1, 2, and 3, are for

25

Specimens that experienced rebounding of the tup from the specimens, while the open
curves, numbered 4-11, are for specimens that experienced penetration of the tup into or
perforation of the tup through the specimens. Penetration was deﬁned as the ﬁrst instant
the tup did not rebound from a specimen. Perforation, however, was deﬁned as the
instant when the tip of the tup just broke throughtheﬂbackside of the specimens being
tested.

6500
5500
4500
3500
2500
1 500

500
-500

 

 

Load,N

 

0 51015202530354045

Deﬂection, mm
Figure 4-2: Load-deﬂection curves of test specimens.

Figure 4-3 shows the energy proﬁle for the eleven curves given in Figure 4-2. The
impact and absorbed energies used in generating the energy proﬁle are based on the
values calculated by the manufacturer’s software. Data points 1, 2, and 3 had impact
energies smaller than the corresponding absorbed energies as the tup rebounded during
these impact tests. Data points 4-8 were located above the equal energy line, indicating
that they absorbed more energy than what was inputted to them. Data points 9 and 11
appeared to be very close to the equal energy line. Inspections of the specimens revealed
that specimens 4 through 11 had been perforated. The absurdity of the results that the

absorbed energy was greater than the impact energy required more careful analysis.

26

01
O

 

 

 

 

 

 

 

 

 

ll

-: :13 if “i f" T ::'i :: :7? a:
gas -~ - ——————~ 4 5 6 91°
5 so -2--- _- -_ .__. _ _ .-
u 25 'i — “ "7 #* —-— —— ._.. ,. 7, . -_ ,,
O _ gg_ __¢_ _ _ g __ _ J __
«2 i2: 3

.-_ f A g _ _
3 1o 4 2 _____ A
< 5 / 1

0 I *I T I
0 1o 20 30 40 so
Impact Energy, J

Figure 4-3: Energy proﬁle of test specimens.

4.3 Frictional Effect

Friction played an important role in the impact study. Six additional test specimens
were impacted to study the ﬁictional effect. These specimens were made of the same
materials as those tested previously. Three Specimens received no lubrication prior to
impact, while the other three were lubricated with a 6% silicone mold release product.
The silicone was spread on the surface of the specimens at the point where the tup would
impact them. The tup was lubricated with silicone as well. Table 4-1 gives the results of
the lubrication test. The impact energies and absorbed energies were obtained from the
manufacturer’s software while the corrected energies and extended method energies were

based on methods presented in later sections.

27

Table 4-1: Results of friction effect tests.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Velocity Based

Software Results Correction Method Extended Method

Test Lubricant E (J) Ea (J) E (J) Ea (J) E (J) Ea (J)
1 No 34.46 35.18 . 34.80 29.45 35.29 27.97
2 No 34.49 32.73 34.83 26.55 35.32 25.24
3 No 34.29 35.64 34.61 26.36 35.13 25.26
4 Yes 34.52 29.75 34.82 25.81 35.32 25.32
5 Yes 34.53 28.89 34.85 25.03 35.31 23.93
6 Yes 34.48 31.08 34.79 26.83 35.27 25.89

 

 

Lubricating the top surfaces of the Specimens and the tup did reduce the absorbed
energy. This was a result of decreasing the friction between the specimens and the sides
of the tup. Less ﬁiction resulted in the load cell recording less load on the tup, thus less
area enclosed by the load-deﬂection curves as shown in Figure 4-4. The load-deﬂection
curves are all very Similar up to the point where the load became nearly constant.

Specimens 4, 5, and 6 have lower constant load values after that point.

5500

 

 

 

4500 -------- ~

 

 

3500 « ~ ~—————~

 

 

 

2500 — - «

Load, N

1 _. _ ___.__.__.

1500 -

 

 

 

 

 

500 ~ - .._

 

 

-500

 

—1

I I I I I I

O 5 10 15 20 25 30 35

Deﬂection, mm
Figure 4-4:Load—deflection curves of lubrication test.

28

4.4 Measurement of Perforation Depth

The deﬂection values used to generate the load-deﬂection curves, like those in Figure
4-4, were based on the calculations mentioned earlier. The deﬂection values were
checked by placing soft green craft foam12.7 mm below the test specimens so that it
would not interfere with the deﬂection. The foam had a density of .0328 g/cm3. The
crosshead was then dropped from various heights. The tup perforated the test specimens
and penetrated into the foam. The value, DM , was the distance measured from the end
of the tup to the top of the undeforrned specimen. The depth of the tup penetration into
the foam, DE , was also measured. The perforation depth, 0}), was calculated by
Equation (4.1) where 50.8 was the length, in millimeters, of the tup and DM was the
measured distance. The value of Dp indicated how far the tip of the tup moved below
the top of the specimen during the impact event.

DP 2 50.8—BM (4.1)

DC was the value given by the manufacturer’s software for how far the tip of the tup
moved below the top of the specimen during the impact event. DE was used to verify
the values of Dp. This could be done by using Equation (4.2) where 12.7 (mm) was the

distance from the bottom of the specimen to the top of the foam and h was the thickness

of the test specimens. The test specimens were 3 mm thick. The values calculated by

Equation (4.2) were labeled D}.

D; = DE +127 + h (4.2)
Table 4-2 gives the values for the dimensions shown in Figure 4-5. Tests 1-4 had the

tup travel through the specimens less than what the manufacturer’s software calculated.

29

Test 5 Showed the calculated perforation to be less than the actual perforation. The

values of DC and Dp Should have been equal. These tests indicate a large discrepancy

between the measurements based on the manufacturer’s software and the soft green foam.

The 0}) and D; values were Similar if not identical. This indicated that this method for

measuring penetration depth was accurate. The Slight discrepancies were due to

measurement errors of the DE values. Friction occurred between the tup and the

specimens after penetration; however, there was also slippage. The slippage was most

likely the reason for the discrepancies between the DC and D}: values. Further

investigations were deemed necessary.

 

 

 

 

ll
1‘

 

 

Tup position
/ after impact

Top of
specimen

2.7 mm

 

 

 

 

/Foam
- Measured foam
penetration

\ Software calculated
deﬂection

 

 

Figure 4-5:Dimensions and notations for tup perforation

tests.

Table 4-2: Results of perforation depth tests.

 

 

 

 

 

 

 

 

 

 

 

Impact .
Test Height (mm) DE (mm) DM (mm) DC(mm) Dp(mm) D‘p(mm) DC - I)P (mm)
1 838.2 6.4 27.0 31.2 22.1 22.1 9.1
2 1066.8 22.2 11.1 46.0 38.1 37.9 7.9
3 965.2 15.9 16.7 45.5 32.5 31.6 13.0
4 965.2 4.8 27.8 45.2 20.6 20.5 24.6
5 965.2 10.3 22.2 9.7 26.2 26.0 -l6.5

 

 

 

 

 

30

The foam did not affect the results as indicated by the load-deﬂection curves of Figure
4-6. Both tests were conducted using the same drop height, h, value. The load-deﬂection
curves are nearly identical with similar peak load values and a constant load value of

about 500 N beginning at a deﬂection of approximately 12 mm.

 

5000
4500 s _._ _ L V-
4000 II .2
3500 A
z 3000 — __ 1%----
g 2500 « .__.----. __ .2
.1 2000 _
1500 ~-
1000 4
500

0 1 T 1 1 1 1 1 1 1 1 ‘1

0 5101520253035404550

Deﬂection, mm
Figure 4-6: Load-deﬂection curves with and without foam.

 

 

 

 

 

 

  
 
 

X FoamL No foam\ 2

 

\/

 

 

4.5 Data Recording

The tup ﬁrst impacted the specimens with its hemispheric nose. The recording of the
load data was started by the ﬂag passing through the emitter/detector. The load data was
recorded continually as the tup advanced into the specimens. The recording of the load
data was terminated when the load became zero or negative. The load value was not zero
when perforation took place for the specimens tested. This was attributed to the sides of
the tup rubbing on the Specimens and the induced shear loads developing into normal
loads at the load cell. Since the data recording unit did not know when the tup perforated
the specimens it kept recording load data even when the load was caused by the sides of

the tup rubbing on the specimens. This caused the time of the impact event to be much

31

longer than it took the tup to perforate the specimens. Consequently, the area under the
load-deﬂection curves was increased. When the load was integrated with respect to
deﬂection, excessive absorbed energies were calculated which did not correctly portray
the behavior of the impacted Specimens. The specimens would seem more resistant to
perforation than what they really were. The excessive recording of load data and the
ﬁiction slippage beyond the penetration point required special attention in the data
analysis.
6500
5500
4500
3500
2500
1 500
500
-500

Load, N

 

0 5 10 15 20 25

Deflection, mm
Figure 4-7: Load-deflection curves of L[(0/90)6] specimens.

4.6 Load-Deﬂection Curves for L|(0/90)6]

Figure 4-7 shows eight load-deﬂection curves of the L[(0/90)(,] Specimens. They all
have a mountain-like shape indicating a signiﬁcant strain softening after the peak force.
The loading sections are slightly concave due to the in-plane constraint caused by the
ﬁxed boundary condition. The eight loading sections seem to overlap up to some extent
and the values of the eight peak forces are very similar. The unloading sections also

overlap well. The overlapping and similarities of the curves indicate the consistency of

32

material properties and testing conditions among the eight specimens. Rebounding
resulted in closed curves while penetration and perforation produced open curves. The
curves of specimens 1-5 have rebounding sections while the remaining curves do not.

Absorbed energies for the specimens with rebounding sections were determined by
calculating the areas enclosed by the load-deﬂection curves. Absorbed energies for the
specimens with open curves, such as specimens 6-8, were determined by calculating the
area bounded by the load-deﬂection curves and the horizontal axis, i.e. the deﬂection
axis. The long tail of the open curves indicated an additional absorbed energy from
friction between the Sides of the tup and the Specimens. This friction occurred after the
tup perforated the specimens. It maintained a relatively constant energy absorption level.
4.7 Calculations of Energies

Figure 4-8 presents the energy proﬁle of the L[(0/90)6] specimens with the load-
deﬂection curves given in Figure 4-7. The absorbed energies were based on the area
enclosed by the curves or under the curves as mentioned earlier. The impact energies,
Ei , were based on the following equation

E ,- = mgh (4.3)

where m was the combined mass of the crosshead, load cell, and tap, g was the
gravitational acceleration, and h was the distance between the tip of the tup and the
surface of the specimens before the drop tests took place.

The impact energy could also be expressed in terms of kinetic energy instead of

potential energy, i.e.

E,- = émviz (4.4)

33

where v,- was the so-called impact velocity measured by the photogate just before the tup
impacted the specimens.

The impact velocity values from the photogate could be veriﬁed by equating the
kinetic energy to the potential energy.

Vi = Zgh (4.5)

The results from the photogate and Equation (4.5) were very similar and should have
been exact if there was no ﬁiction between the crosshead and guide rails.

Three of the ten points corresponding to specimens 6, 7, and 8 had absorbed energy
values greater than their respective impact energies. Apparently, the calculations of the

energies were not correct and required more careful analysis.

 

42

 

as
l

l

l

l
1.

 

 

Absorbed Energy, J

 

 

 

 

 

28 30 32 34 36 38 40 42

Impact Energy, J
Figure 4-8:Energy proﬁle of L[(0/90)¢] specimens.

The absorbed energies calculated from integrating the load-deﬂection curves, as
mentioned earlier, covered the entire load-deﬂection curves. More Speciﬁcally, they
included the period of friction between the tup and the specimens after the composite

plates were completely perforated. Accordingly, the absorbed energies calculated by the

34

integration of the entire load-deﬂection curves did not really reﬂect the energy absorption
capability of the composite plates. They were higher than the composite plates could
take. The calculation of the energy absorption capability would be correct if the load-
deﬂection curves ended at the perforation points, instead of at the ends of the impact
events.

4.8 Correction of Energy Calculations

4. 8. 1 Correction of A bsorbed Energy

Based on the forgoing discussion, a method was developed to correct the values of the
absorbed energy given by the manufacture. This method utilized the perforation point as
the ending point of energy integration and was useful for the specimens with open load-
deﬂection curves. However, this method did not apply to the specimens with closed
load-deﬂection curves because there was no ﬁiction between the tup and the specimens
due to the rebounding process.

The goal of the drop weight testing was to determine the amount of the energy that
each Specimen could absorb up to perforation. The corresponding velocity-deﬂection
curve was used to determine the perforation point. The reason was that the velocity-
deﬂection curves leveled off once perforation occurred due to the steady process of
friction, i.e. no further damage process in the composite plates. Figure 4-9 presents the
load-deﬂection curve and the corresponding velocity-deﬂection curve of L[(0/90)6]
specimen 8.

The load value in Figure 4-9 increased quickly, reached a peak value of 5923 N, and
then decreased sharply. The load value then leveled off and became nearly a constant

value of 400 N. Friction between the sides of the tup and the specimen started when the

35

load became nearly constant. The point where the load became constant was deemed the

 

 

 

perforation point.
6000 4-5
Velocity ‘“ 4
5000 -~ 3 5
4000 —1 Load " 3 '2"
Z
6 L ~— 2.5 3"
8 3000 ~ Tangent line __ 2 '5
.1 ' 2
2000 l - - Perforation -_ 15 g
: —— 1
1000 1 ' o 5
o 1 1 1 1 i 1 + 1' i 0

 

058111214151718

Deflection, mm
Figure 4-9:Load and velocity curves of L[(0/90)6] specimen 8.

The velocity curve began with a value of 4 m/s which corresponded to the impact
velocity. The velocity decreased as the tup was in contact with the specimen. There was
then a bend in the curve as the load approached the peak value and then the velocity
decreased at a constant rate along the unloading section of the load-deﬂection curve.
Another bend occurred in the velocity near the end of unloading. The velocity decreased
constantly again after that point. The starting point of the second constant decrease in
velocity was indicative of the starting point of constant friction between the sides of the
tup and the Specimen. Thus, the constant decrease in velocity began when the tup
perforated the specimens. A tangent line with respect to the velocity-deﬂection curve
was drawn to identify the perforation point as Shown in Figure 4-9. Another ﬁtting line
was drawn on the load-deﬂection curve, also shown in Figure 4-9. The perforation points

determined by the load and velocity curves agreed were very close.

36

This method of determining the perforation points was similar to that used by Baucom
and Zikry [18]. In their study, the specimens were deemed perforated when the tup
displacement reached a value that was equal to the sum of the specimen thickness and the
diameter of the hemispheric nose. However, their impact testing was conducted under
quasi-static loading rates (10-80 urn/s). They also observed a point where the load
became a nearly constant value.

Based on the perforation points determined from the velocity-deﬂection curves, the
absorbed energy values that matched the deﬂection values at perforation were used as the
corrected absorbed energies. This method of correcting the absorbed energy was
subsequently used for all Specimens that were perforated.

4. 8.2 Correction of Impact Energy

The original method used Equation (4.3) or Equation (4.4) to calculate the impact
energy. This method did not take into account the energy introduced to a specimen by
the crosshead, load cell, and tup during the impact, i.e. from the contact impact until the
end of the impact event. This additional impact energy could be characterized as

potential energy in the following equation.
15f1 = mgh' (4.6)

This additional energy had to be added to the impact energy calculated by Equations (4.3)
or (4.4) in order to have the correct impact energy.

The value of h ’ was the tup deﬂection beyond the top surface of the specimen after the
initial contact took place. The method for determining h ’ was dependent on whether the
tup rebounded or perforated the Specimens. The maximum deﬂections calculated by

Equation (3.3) were used if the tup rebounded from the specimens. The deﬂection values

37

corresponding to the perforation points found from curves like those presented in Figure
4-9 were used if the tup perforated the specimens.

Equations (4.3) and (4.6) could be combined into Equation (4.7) to calculate the
corrected impact energy.

Eic = mgh + mgh' (4.7)
= mg(h + h')

Eliminating the absorbed energy due to the post-perforation friction, i.e. the corrected
absorbed energy, and calculating the impact energy with Equation (4.7), i.e. the corrected
impact energy, gave the energy proﬁle of the L[(0/90)6] shown in Figure 4-10. None of
the points are located above the equal energy line. Also, none of the points are located on
the equal energy line, which implies that there was energy loss due to heat and vibration

during the impact events.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

41

40 ._ ___.
_, 39 —— —- —--————-._
g 361::___:i__- / WW8"
'" 35 f ' .7 __-_-. ___-
E 34 _ /g5 _
3 33 «»_.—.~—_-_ A 6;_3_.-______.---- ___
.o 32 --_-_-_-____ . -----_---
“ 31 «- ~ ----- 2 - ..-_-

30 - —— 1. - - ___.

29 1 1 1 1 1 1 1 T 1 1 T

29 3O 31 32 33 34 35 36 37 38 39 40 41
Impact Energy, J

Figure 4-10: Corrected energy proﬁle of L[(0/90)6] specimens.
The corrected method would abruptly end the load-deﬂection and velocity-deﬂection
curves at the perforation points. The testing showed the loads gradually decreasing to

zero after the friction portions of the load-deﬂection curves. The corrected energy

38

method did not take into account this small area. This area only accounted for
approximately 0.5 J of energy so it was deemed negligible.
4.9 Other Correction Methods

The corrected energy methods for obtaining corrected impact energy and corrected
absorbed energy seemed to characterize the energy absorption capabilities of the
specimens more accurately than using the method provided by the manufacturer. Other
methods were also investigated in attempts to correct the absorbed energies.
4. 9. 1 Friction Removal Correction Method

The ﬁrst method used the measured perforation depth and the load-deﬂection curves
to correct the absorbed energy. This method began by testing a Specimen with the
instrumented drop-weight impact tester. Absorbed energy needed correction only if the
tup perforated the specimens. The distance from the end of the tup to the top of the
specimens was measured by a ruler after the tup had ﬁnished moving through the

specimens. This measured distance, DM , is shown in Figure 4-11. The distance that the
tup moved through the specimens while encountering friction between the sides of the
tup and specimen could then be calculated by

D}? =46-DM (4.8)
where 46 was the length, in millimeters, of the side of the tup, and DF was the ﬁiction

distance.

39

 

 

 

 

 

DM
Specimen v 46 mm
:1 50.8 mm
Tup —' Dr

 

 

 

 

U—L” J,

Figure 4-11: Tup measurements made
for friction removal correction method.

The friction distance, D}: , was then removed from the tail of the load-deﬂection

curve of each specimen that had been perforated as illustrated in Figure 4-12 for test 6 of

the test Specimens. The friction distance was 27 mm so the portion of the load-deﬂection '

curve between 13 mm and 40 mm was removed. The remaining portions of the curve up

to 13 mm and between 40 mm to 43 mm were joined together. The new load-deﬂection

curve, Figure 4-13, could then be used to calculate the absorbed energy. There was a

discontinuity in the load at a deﬂection of 13 mm. This occurred because the load was

not equal at deﬂections of 13 mm and 40 mm.

Load, N

4500
4000
3500
3000
2500
2000
1 500
1 000
500
O

 

 

0 51015202530354045

Deﬂection, mm

Figure 4-12: Removing friction distance of test specimen 6.

40

 

4500
4000 a
3500 -
3000
- 2500 J -
2000 3
1500
1000 -- ..___-___ ___-. .______ ’ T " ‘

5004 » -
0 \

024681012141618

Deﬂeeﬁon,nun
Figure 4-13: Modiﬁed load-deﬂection curve of test specimen 6.

 

 

 

Load

 

 

 

 

 

 

The friction removal correction method was used on test specimens 6 and 7 to correct
the absorbed energies and impact energies. Their original lead-deﬂection curves are
shown in Figure 4-2. The results for the correction method and ﬁiction distance
correction method are given in Table 4-3. The impact energies were similar because
different h ’ values were used in the calculations, but the absorbed energies were not. The
absorbed energy values are greatly affected by the load-deﬂection curves. The ﬁiction
removal correction method was not as accurate as the velocity based correction method
because it used the deﬂection values calculated after perforation, hence the ﬁiction
portion of the load-deﬂection curves, where a portion was removed, could have been
incorrect. The deﬂection values were shown to be questionable in Section 4.4.

Some of the tests could not have the ﬁiction removal subtraction method used. This
was because when the friction distance was subtracted, the load-deﬂection curves would
end in the unloading portions. Friction did not occur during the unloading portions so the

load-deﬂection curves must have been incorrect beyond the perforation point.

41

 

 

 

 

Table 4—3: Results of friction removal correction
method.
Velocity Based Friction Removal
Correction Method Correction Method
Test 810) E. 0) E10) 13.0)
6 37.41 26.64 37.61 27.86
7 38.24 26.87 39.01 32.36

 

 

 

 

 

 

 

4. 9.2 Extended Method

Another way to correct the energy absorbed by the specimens was termed the
extended method. This method was based on extending the unloading section (excluding
the rebouding part) to the deﬂection axis for both closed and open load-deﬂection curves.
This method was used as a way to estimate the amount of energy required for perforation.
The absorbed energy calculated by the extended method would be larger than the values
calculated by the corrected method for specimens that had a rebounding section. The
triangle method could be used as a way to predict penetration energy even if the tup
rebounded during testing.

The load-deﬂection curve of the L[(0l90)6] specimen 4 is presented in Figure 4-14.
The tup rebounded from this specimen as is evidenced by the curve being closed. This
Specimen could have absorbed more energy while being penetrated by the tap. The
unloading section of the curve would have continued along its slope and intersected the
deﬂection axis at a point beyond 12 m if the tup had penetrated the specimen and not
rebounded. This extension of the Slope is shown by the dashed line. The post-
perforation friction would not have occurred because the Sides of the tup did not pass
through the Specimen. The extended load-deﬂection curve could be used to calculate the

absorbed energy for penetration. The impact energy could also be corrected using

42

Equation (4-5) where h ’ would have been the deﬂection value at the intersection of the

softening curve and the deﬂection axis as indicated in Figure 4-14. Figure 4— l 5

illustrates how the extended method would be used for specimens that were perforated.

The load recorded due to friction would not be used for calculating absorbed energy.

Load, N

6000

 

5500 -
5000 - -
4500 - -
4000 - -

 

 

3500 -»-
3000 ---_
2500
2000 .-

 

 

1500

 

 

1000
500 -

 

 

 

0 r

 

‘A‘A

 

0 2

114

6 8 h.

Deflection, mm

10 12

Figure 4-14: Extended method for L[(0/90)¢] specimen 4.

Load, N

6000

 

5500

 

 

5000
4500

 

 

4000 +- I l

 

 

3500 4—- All
3000 “F” A]

2500
2000

 

1500 a—le
1000

500 I

 

 

 

 

otII
0246

 

I I I I I I I

8 10 12114 16 18 20 22 24
Deﬂection, mm

Figure 4-15: Extended method for L[(0/90)5] specimen 8.

43

This method would not work well if there was not a well deﬁned unloading section of
the load-deﬂection curve. Specimens l and 2 of the L[(0/90)6] plate could not be used
for the extended method since they did not have well deﬁned unloading sections. Table
4-4 presents the absorbed energies and impact energies of the L[(0/90)6] specimens from
the results based on the manufacturer’s software, velocity based correction method, and
the extended method.

Table 44: Comparison of absorbed energy correction methods.

 

 

 

 

 

 

 

 

 

 

| Software Results Velocitv Based Correction Method Extended Method
Specimen TupI Ei (J) Ea (J) h' (mm) Ei (J) Ea (J) Ei'Ea (J) h' (mm) Ei (J) Ea (J) h' (mm)

1 Rb 32.65 29.57 10.15 33.15 29.57 3.58 10.15 - - -

2 Rb 34.09 31.66 10.46 34.60 31.66 2.94 10.46 - - -

3 Rb 34.76 33.11 10.77 35.29 33.11 2.18 10.77 35.32 36.00 11.50
4 Rb 33.64 33.24 11.72 34.22 33.24 0.98 11.72 34.26 34.89 12.80
5 Rb 34.46 34.17 11.47 35.03 34.17 0.86 11.47 35.04 35.23 11.80
6 Pr 34.49 35.16 13.46 35.06 33.90 1.16 11.43 35.07 34.14 11.80
7 Pr 36.53 37.27 15.49 37.10 35.45 1.65 11.68 37.11 35.70 12.20
8 Pr 40.16 41.28 24.38 40.77 36.85 3.92 12.45 40.73 36.10 11.80

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The velocity based correction method and the extended method produced similar
results. The extended method absorbed energies for tests 3-5 are greater than the velocity
based corection method absorbed energies because those tests had rebounding. The
extended method shows how much energy may have been required to penetrate but not
perforate the specimens for tests 3-5.

Both methods had corrected the impact energy to include the additional energy in the
form of mgh '. The h ’ values for each method were similar as shown in Table 4-4. The
velocity based correction method had all absorbed energies less than the impact energies,
while the extended method had absorbed energies slightly greater than impact energies
for tests 3-5. These tests had rebounding sections so the absorbed energies are an

estimate of how much they could have absorbed. Another possible explanation is that the

extended unloading slope could have intercepted the deﬂection axis at a value greater

than it would have in actual testing leading to an overestimate of the absorbed energy.

45

5. Experimental Results and Discussions

The velocity based correction method was chosen to present the energy data for all of
the specimens tested. This method effectively eliminated the absorbed energy resulting
from the sides of the tup and Specimen interactions. It also gave more representative
values for the amount of energy being inputted to each Specimen.

The load-deﬂection curves, energy proﬁles, and energy values used to characterize
some representative samples are given below. The results of other specimens are given
in Appendices C-F.

5.1 Load-Deﬂection Curves and Energy Proﬁles
5.1.1 Laminated Specimens

Five different laminate conﬁgurations were tested. They were designated as L[(0/0)(,]
with 0 being equal to 75°, 15°, 30°, 45°, and 90°. The load-deﬂection curves of the
L[(0/90)(,] specimens along with their energy proﬁles are shown in Figures 5-1 and 5-2,

respectively. The load-defection curves and energy proﬁles for the other laminated

6500
5500
4500
3500
2500

Load, N

1500
500

 

-500
0 5 10 15 20 25 30

Deflection, mm
Figure 5-1:Load-deﬂection curves of L[(0/90)6| specimens.

46

specimens, i.e. L[(0/7.5)6], L[(0/15)6], L[(0/30)(,], L[(0/45)(,], are given in Appendix D.

 

41
4o ..--_______ ______ ._-_ _-__ ._- _- -_ -, - ______
39 +~——————--—~——~6V7- ———— —------ -— --
38 _p__ ____ -__ ______ __ ____-_7 _ .-_ LL- _ -.
37 new: —— —- — __ __ -

36 ~ - - - - - ,
35 J... 2. ._ / :_‘Z_ __ .2 _-- _--
34 «~«-——— fes —~

4. 6 3
33 .—————————— -# ﬁ- ~ -
/

32 ——+—* -
31 -~———— -—— w.
30 _F._ __ . .-_____.___--_ _

1.
29 1 1 1 1 1 1 T 1 1 1 T

29 30 31 32 33 34 35 36 37 38 39 40 41

Impact Energy, J
Figure S-2:Energy profile of L|(0/90)5] specimens.

 

 

 

 

Absorbed Energy, J

 

 

 

 

 

The load-deﬂection curves of the specimens tested seem to overlap well in the loading
and unloading sections, indicating consistency in both material properties and testing
conditions. Specimens 2-6 were chosen to illustrate the penetration and perforation
thresholds of the L[(0/90)(,] specimens. Specimens 2-5 were chosen because they were
almost penetrated by the impact energy inputted to them. Specimen 6 was chosen
because its value of impact energy just caused perforation. Specimen I experienced little
damage and was not near to penetration so it was not used. Specimens 7 and 8 had
severe perforation and were not used to characterize the specimens. The impact energy,

E,- , and absorbed energy, Ea , of these specimens are given in Table 5-1. The range of

absorbed energy for penetration and perforation was 31.66 J to 34.17 J. The difference

between 51' and Ea is also shown. These values indicate how much more absorbed

energy would have been needed to put the data points on the equal energy line. The

minimum value of them could be considered as the minimum energy not absorbed by the

47

specimens due to vibration and heat. The minimum difference was 0.86 J for the
L[(O/90)(,] specimens. The last column in Table 5-1 indicates whether the tup rebounded,

Rb, penetrated, Pn, or perforated, Pr.

 

 

 

 

 

 

 

 

 

 

 

Table 5-1: L[(0/90)d s secimens.
Specimen Ei (J) Ea (J) Ei‘Ea (J) Rb, Pn, Pr
1 33.15 29.57 3.58 Rb
*2 34.60 31.66 2.94 Rb
*3 35.29 33.11 2.19 Rb
*4 34.22 33.24 0.97 Rb
*5 35.03 34.17 0.86 Rb
*6 35.06 33.90 1.16 Pr
7 37.10 35.45 1.65 Pr
8 40.77 36.85 3.92 Pr
*Average 34.84 33.21

 

 

 

 

 

 

Rb is rebounding, Pn is penetration, and Pr is perforation

5. 1. 2 Stitched Specimens

The stitched Specimens produced the load-deﬂection curves shown in Figure 5-3.
These curves seemed to be very consistent as they overlapped very well in the loading
and unloading sections. They were used to establish the energy proﬁle Shown in Figure
5-4. Table 5-2 gives the impact energy and absorbed energy for specimens 5-7 as well as
their difference and whether the tup rebounded, penetrated, or perforated. Only
specimens 5-7 were used to characterize the penetration and perforation thresholds of the
stitched specimens, while specimens 1-4 and 8 were not. Specimens 1-3 had the tup
rebound while specimens 4 and 8 were largely perforated. They were not close to either

the penetration threshold or the perforation threshold.

48

 

 

 

 

 

 

 

 

 

 

 

 

Deﬂection, mm
Figure 5-3: Load-deﬂection curves of S[(0/90)6] specimens.

41
40
39
38
37
36
35
34
33
32
31
30
29

Absorbed Energy, J

 

29 30 31 32 33 34 35 36 37 38 39 40 41

impact Energy, J
Figure 5—4: Energy proﬁle of S[(0/90)5] specimens.

The range for the penetration and perforation thresholds was from 36.61 J to 37.60 J.
The unabsorbed energy was about 0.64 J as indicated in the fourth column of Table 5-2.

The complete results are given in Appendix E.

49

Table 5-2: Stitched specimens.

 

 

 

 

 

 

 

 

 

 

 

 

 

Specimen 51 (J) Ea (J) Ei'Ea (J) Rb, Pn, Pr
1 35.58 34.63 0.96 Rb
2 36.42 34.90 1.52 Rb
3 36.75 34.48 2.27 Rb
4 36.91 35.25 1.66 Pr
*5 37.73 36.44 1.29 Rb
*6 38.24 37.60 0.64 Rb
*7 38.70 36.61 2.09 Pr
8 40.60 36.34 4.26 Pr
*Average 38.22 36.88

 

 

 

 

Rb is rebounding, Pn is penetration, and Pr is perforation

5.1.3 T wo-Dimensional Woven Specimens

The load-deﬂection curves of the 2D[(m99_)6] specimens are Shown in Figure 5-5. All
of the curves are similar with overlapping along the loading and unloading sections. The
corresponding energy proﬁle is shown in Figure 5-6. The impact energy and absorbed
energy values are given in Table 5-3. Specimens 1-4 were chosen to characterize the
penetration and perforation resistance of these specimens. Specimens l and 3 had the tup
rebound while specimens 2 and 4 were perforated. The remaining Specimens were
caused by large amounts of perforation so they were not used. The range of the
penetration and perforation thresholds was 32.40 J to 35.86 J. The unabsorbed energy for
specimen 3 was 0.07 J indicating that it was very close to the equal energy line. Column
5 of Table 5-3 indicated that the tup penetrated specimen 3 but did not perforate. This
behavior gave a good indication of how much energy the specimens could absorb and no
correction had to be made to the absorbed energy. The complete results are given in

Appendix F.

50

Load, N

6500
5500
4500
3500

 

2500

 

1 500
500

 

-500
0 5 10 15 20 25 30

Deflection, mm

Figure 5-5: Load-deﬂection curves of 2D|(0/90)6] specimens.

Absorbed Energy, J

41
40
39
38
37
36
35
34
33
32
31
30
29

 

 

 

29 30 31 32 33 34 35 36 37 38 39 40 41
Impact Energy, J

Figure 5-6: Energy proﬁle of 2D[(0/90)5] specimens.

51

 

 

 

 

 

 

 

 

 

 

Table 5-3: 2D[(0/90)5] s secimens.
Specimen E (J) Ea (J) Ei'Ea (J) Rb, Pn, Pr
*1 34.53 33.50 1.03 Rb
*2 35.22 34.30 0.92 Pr
*3 35.93 35.86 0.07 Pn
4 36.56 32.40 4.16 Pr
5 37.11 34.33 2.78 Pr
6 38.21 36.61 1.60 Pr
7 40.82 33.77 7.04 Pr
*Average 35.23 34.55

 

 

 

 

 

 

Rb is rebounding, Pn is penetration, and Pr is perforation

5.1.4 T [tree-Dimensional Woven Specimens

Four three-dimensional woven plates, 3D[((lQ)6], were tested. The angles, 0, were
15°, 30°, 45°, and 90°. The load-deﬂection curves of the 3D[(0/ﬂ)6] Specimens are
shown in Figure 5-7. The curves are not as consistent as the specimens mentioned
earlier. This implies that there were large variations in the material properties of some of
the specimens. This was likely a result of the fabricating process. The ﬁrst 3D
Specimens made were the 3D[(ﬂ0)6] and it is likely that the weaving process was not
reﬁned. The remaining 3D woven specimens, presented in Appendix G, seemed to have
smaller variations in the load-deﬂection curves which could be attributed to improved
fabrication skills. The energy proﬁle of the 3D[(M)6] specimens is shown in Figure 5-
8.

None of the data points are located right on the equal energy line. Specimens 3, 5, and
6 were used to characterize the penetration and perforation thresholds of the specimens.
The penetration and perforation thresholds seemed to occur between 34.28 J and 35.75 J.
The amount of unabsorbed energy was approximately 0.47 J. Specimen 4 was not used
because its load-deﬂection curve was not Similar to the others indicating that its material

properties were different. Specimens 3 and 5 had the tup rebound, while specimen 6

52

experienced perforation. Specimen 1 had the tup rebound and was not close to
penetration. Specimen 2 was perforated but its load-deﬂection curve was not matching
the others so it was not used. Specimens 7 and 8 had large amounts of perforation and
were not used. The impact energies and absorbed energies of the specimens are given in

Table 5-4.

 

6500 -
5500 L
4500
3500
2500
1500
500
-500

Load, N

 

 

 

 

 

 

 

0 5 1O 15 20 25 30

Deﬂection, mm
Figure 5-7:Load-deflection curves of 3D[(0/90)6| specimens.

 

 

 

 

 

Absorbed Energy, J
8
l
l
l
1
~31
J
1
1
l

 

 

 

29 30 31 32 33 34 35 36 37 38 39 40 41

Impact Energy, J
Figure 5-8:Energy proﬁle of 3D[(0/90)6] specimens.

53

Table 5-4: 3D[(0/90)6] specimens.

 

 

 

 

 

 

 

 

 

 

 

 

 

Specimen Ei (J) Ea (J) Ei'Ea (J) Rb, Pn, Pr
1 34.57 33.38 1.19 Rb
2 35.02 29.56 5.46 Pr
*3 35.88 35.41 0.47 Rb
4 36.47 30.78 5.69 Pr
*5 37.00 34.28 2.73 Rb
*6 37.48 35.75 1.73 Pr
7 38.15 37.38 0.77 Pr
8 40.52 32.23 8.29 Pr
*Average 36.79 35.15

 

 

 

 

Rb is rebounding, Pn is penetration, and Pr is perforation

5.2 Discussions

All specimens produced similar results when compared to the L[(0/90)6] specimens.
None of the Specimens had impact energies exactly equal to their respective absorbed
energies. An amount of energy less than 1 J seemed to be lost in the tests due to vibration
and heat for all tests. The energy proﬁles produced from the testing data were not able to
determine the exact penetration and perforation. None of the samples had a large impact
energy interval between penetration and perforation. This was likely due to the specimens
being very thin. There was no remaining material for the tup to penetrate into once it
made initial penetration. The testing results did reveal a range of impact energies for
each specimen where the tup would almost penetrate or just perforate.The range of
impact energies seemed to be a method for characterizing the ballistic performance of
each specimen.
5. 2.] Angle Effect

The testing results revealed that ﬁber orientation had an inﬂuence on penetration and
perforation thresholds. Figure 5-9 showed that penetration and perforation thresholds, for

laminated specimens, increased as the ﬁber angle, 0, was decreased. This was believed to

54

be caused by the bending stiffness mismatch in the specimens. The bending stiffness
mismatch was dependent on the difference of ﬁber orientation between adjacent laminae.
It increased as the difference of ﬁber orientations was increased. This bending stiffness
mismatch caused the composite specimens to delaminate when the interlaminar stress
was higher than the allowable levels. Once delamination formed, the tup could perforate
the delaminated specimens easier than specimens that were not delaminated [5, 17, 19].
The results of Figure 5-9 seemed to support this hypothesis. Small values of 0 caused the
specimens to delaminate less, hence increasing the penetration and perforation thresholds.
The L[(0/90)6] specimens had the largest bending stiffness mismatch causing the largest
delamination, thus the lowest penetration and perforation thresholds. On the contrary, the
L[(0/7.5)(,] and L[(O/15)6] specimens had smaller bending stiffness mismatch causing less
delamination, thus larger penetration and perforation thresholds.

The results of the three-dimensional woven Specimens given in Figure 5-10 showed a
similar dependence on ﬁber orientation except for a small discrepancy in the 3D[((_)/_9§)(,]
specimens. As mentioned earlier, the load-deﬂection curves of the 3D[(Q/_9_Q)6] were not

as consistent as other cases and that might be responsible for the discrepancy.

55

 

a s

 

 

 

 

 

 

 

3 O
538‘ I
s 1 A
5 37 0 A
’5
535 E
:5 8
0
34 O
LI(U7-5)al Ll(015)al 180318 11045161 LEW
Whoa
Figure 5-9:Impact energy interval of laminated specimens.
40
e
39 1
e
'4- 38 . A
5 1 .
0
.ﬁ 37 4 . A I e
a . -
I
35 «
34
3Dllﬂ1§lsl 3011331361 301M161 3010/2911]

Specimen Type
Figure 5-10: Impact energy interval of 3D specimens.

5. 2. 2 T hrough-T hickness Eﬂect
The specimens tested have had varying degrees of through-thickness reinforcement.
The laminated specimens had no through-thickness reinforcement. The only material

joining the plies was the thin layer of matrix between them. There were no ﬁbers

contributing to any through-thickness strength.

56

The stitched specimens and laminated specimens were similar in that they were both
initially L[(0/9O)6] specimens. The stitched specimen used 1 mm wide strips of prepreg
as stitching thread to join the plies together. Stitching through the thickness with a 12.5
mm x 12.5 mm square pattern proved to be the best through-thickness reinforcement
method, among the composites tested, as shown in Figure 5-11. It was likely that this
stitching pattern was an efﬁcient selection. A stitching pattern with large dimensions
may not have been efﬁcient enough. On the other hand, a stitching pattern with smaller
dimensions may have caused higher stress concentrations.

Each piece of the two-dimensional woven specimens consisted of two plies that were
interwoven. This interweaving reinforced each piece. Six pieces were then stacked
together to form the completed two-dimensional woven specimens. As a result, the two-
dimensional woven specimens had more through-thickness reinforcement than the
laminated specimens. This caused the two-dimensional woven specimens to require
slightly more energy to begin penetration and perforation than the laminated specimens.
Thus, the two-dimensional woven specimens had higher penetration and perforation
thresholds than the laminated specimens.

The three-dimensional woven specimens were reinforced through the thickness by
ﬁbers although they were not oriented in the thickness direction. This made them more
resistant to penetration and perforation when compared to the two-dimensional woven

and laminated specimens.

57

 

 

 

394
e
o
2:38—
2' o
0 X
i537~ x
E
35— 3 x
0 x
34 °

 

Lao/90).] melee.) 30t<_0390)61 sue/30).]
Specimen Type
Figure 5-11: Impact energy interval of [(0/90)5] specimens.

 

 

 

 

40
e
39 .
,
>2 38 « + . A
g? + A e
if. 37 ~ 4: 9 a I e
‘3' A
_g 36 ‘ e E e
35- ' 8
o
34 o
L[(O/7.5)6] L[(Ol30)6] L[(0/90)el
Lao/15).] 30mm») ”(0’45)“ madame]
soumw SDKMM
Speclmen Type

Figure 5-12: Impact energy interval of specimens with equal 0.

The 3D woven plates were fabricated with four different 6 values that were 15°, 30°,
45°, and 90°. Four of the laminated plates shared the same 9 values. The results from the
testing of these specimens are shown in Figure 5-12. The solid symbols represent the 3D

woven specimens. The L[(O/7.5)(,] results are shown for comparison. The 3D woven

58

specimens had larger energy intervals than the laminated specimens. This was the most
obvious when looking at the results of the 3D[(Q/_l_5_)6] specimens. The 3D[(_(M)6]
specimens performed slightly better than L[(O/3O)6] specimens. The testing results
showed less impact energy was required to begin perforation in the 3D[(w)6]
specimens when compared to the L[(O/45)6] specimens. The energy interval for the
3D[(M§)6] specimens was larger while the energy to cause perforation was greater. The
3D[(_(_)L9_(_))6] specimens showed the largest improvement on penetration and perforation
resistance when compared to the L[(O/9O)6] specimens with the same 9 value. The 3D
woven specimens increased penetration resistance by nearly 1.7 J. Perforation resistance
was increased by over 2 J. Visual inspection showed a decrease in delamination area,
which seemed to not propagate as far from the impacted area as in the other specimens.
The undulations in the 3D woven fabric seem to retard the delamination growth.

Figure 5-13 compares L[(O/45)6] specimen 5 to 3D[(Q/15_)6] specimen 6. They were
subjected to impact energies of 36.39 J and 36.42 J, respectively. Delamination is shown
by the darker areas of the specimens when the specimens are placed on a light table and
photographed. The laminated specimen delaminated more than the 3D woven specimen.
The delamination of the bottom ply extends almost the entire length of the specimen.
The 3D woven specimen delamination seemed to be constrained to the center of the

specimen; it passed slightly beyond the undulations of the warp and ﬁll strips.

The delamination of 2D[(M)6] specimen 1 and 3D[((_)L9_0)6] specimen 1 is
compared in Figure 5-14. The specimens were impacted with energies of 34.53 J
and 34.57 J, respectively. The delamination area of the 2D specimen was larger

than the 3D specimen. The 2D specimen had delamination extend away from the

59

impact point. The 3D specimen seems to contain the delamination to an area close

to the point of impact, i.e. at the center of the unit cell.

 

L[(0/45)6] 3D[(Q/_4§)6]
Figure 5-13: Delamination of L[(0/45)6] and 3D[(0/45l6] specimens.

20[(Qﬂ)6] 3D[(ﬂ9_0)6]
Figure 5-14: Delamination of 2D[(0/90)6] and 3D[(0/90)6] specimens.

 

5.3 Composite Damage

All specimens were damaged when they were impacted with the tup. The amount of
damage depended on the impact energy and type of specimen. Figures 5-15 and 5-16
show the damage of the 3D[(M)6] specimens observed from the top and bottom
surfaces, respectively. The specimens were placed on a light table and photographed.

The specimens are arranged in order of increasing impact energy. Each specimen is

60

labeled with its test number and impact energy. The numbers are consistent with those
used in the corresponding load-deﬂection curves, energy proﬁle diagrams, and
summarized data tables. Pictures of all other specimens are given in Appendices H-K.
The dark area at the centers of the specimens is a combination of delamination and
ﬁber breakage. Specimens 3-5 were penetrated so the tup did not pass through the
specimens. Specimen 2 in Figure 5-15 has been perforated as light can be seen through
the center. The dark regions are larger in Figure 5-16 as more delamination occurred on

the bottoms of specimens.

61

 

Figure 5-15: Top view of damage to 3D|(0/45)5] specimens.

62

 

Figure 5-16: Bottom view of damage to 3D[(0/45l6] specimens.

63

5.4 Material Behavior and Through-Thickness Reinforcement Hypotheses
The testing has shown that through-thickness reinforcement and small angles between

adjacent plies increases penetration and perforation resistance. Plotting the normalized

mismatch of DH and D16 bending stiffness values for a two-ply laminate in Figure 5-l 7
reveals correlation with the testing results. The mismatch of D1 1, has a value of zero

when the ﬁbers of both plies are in the same direction. D11 is calculated from Equation

(5.1).

n
1 _
011=32911(h2—h2_1) (5.1)
k=1

The mismatch of D] I has a maximum value when the angle between the adjacent plies is

90°. The mismatch of D11 can be correlated with the amount of delamination that occurs

when composite plates are subjected to transverse load. There is no delamination when
the ﬁbers of adjacent layers are oriented in the same direction. The delamination area
increases and reaches a maximum when the ﬁbers in each ply are orthogonal to each
other, i.e. the largest possible difference of ﬁber angles between adjacent plies.
Delamination reduces a laminated composite to individual plies that can be easily

penetrated and perforated.

The D16 mismatch curve seems to correlate with the penetration and perforation

resistance of the laminated and 3D woven specimens. D16 is calculated from Equation

(5.2).

64

n
1 — 3 3
016 = 51:19:th — 11H) (5.2)

The mismatch of D16 has a maximum value at 30°. The laminated and 3D woven

specimens have their largest penetration and perforation thresholds at small 0 values of
30° or less. It appears that both of these play a role in causing the specimens to absorb

energy.

 

AA ﬂ
0.8 “‘.—“ 7 X __-.__ A
0.6 +

D, N.m

 

 

o I l l l l l I I
0 10 20 30 4O 50 60 70 80 90

0, degrees

 

Figure 5-17: Normalized D11 and D16 values for two-ply laminate.

In addition, the through-thickness reinforcement seems to constrain the delamination
cracks from spreading away from the impact points. Less delamination causes the tup

greater difﬁculty in perforating the specimens.
A composite specimen with a D16 value not equal to zero indicates that when

subjected to bending loads it will also twist, i.e. there is coupling. This coupling may

change the direction of the tup on impact causing the tup to strike the specimen at an

65

angle of less than 90° to the specimen surface, i.e. oblique impact. Oblique impact could

allow the specimens to have higher penetration and perforation resistance.

66

6. Conclusions and Future Study
6.1 Conclusions

Composite plates made from glass/epoxy were laminated, stitched, and woven with
two-dimensional and three-dimensional fabric geometries. Laminated specimens
constructed with 9 angles of 75° and 15° had higher penetration and perforation
resistance than specimens with 6 angles of 30°, 45° and 90°. These results supported the
hypothesis that small ﬁber angle values can increase penetration and perforation
resistance. The stitched specimens had the largest penetration and perforation thresholds.
The three-dimensional woven specimens outperformed the laminated and two-
dimensional woven specimens. The 3D[(ﬂ5_)6] and 3D[(w)6] had larger
penetration and perforation thresholds than the other three-dimensional specimens,
which supports the ﬁber angle effect. The three-dimensional woven geometry was
shown to have good impact resistance most likely due to the innovative way of linking
each ply together.

6.2 Future Study

The time spent fabricating and testing specimens revealed many things that could be
changed or made better to ensure testing gave the desired results.

The ﬁrst area deals with creating the samples. The laminated samples were not
difﬁcult to create. Maintaining the correct ﬁber angle for each ply was important for
creating good specimens. The fabrication of the stitched panel was time consuming
because the thread would break often. Friction between the thread and needle eye and the

thread and plies was the cause. The 2D woven and 3D woven samples would be more

67

easily made if a loom were used. A small handloom could be used for making the 2D
woven fabric if dry ﬁbers were used. Dry ﬁbers would allow the tow width to be varied.

Testing had shown that the 3D woven geometry improved impact resistance when
compared to laminated and 2D woven specimens. More testing could be conducted to
reinforce the results of the current study. Other ﬁbers could be tested such as carbon and
Kevlar. Smaller tow widths would decrease the unit cell size possibly leading to an
increase in the penetration and perforation thresholds. Automation of the weaving would
increase the ability to test more ﬁber types and weaving angles while reducing the time
needed to create each plate. The cost of a fully automated machine would be very
expensive and a machine may not exist that could weave the 3D weave geometry. The
best choice would be to modify a purchased loom so that the 3D weave geometry could
be achieved. A loom would require dry roving to be used so the woven fabric would
have to be infused with resin using a method such as vacuum assisted resin transfer
molding or by pouring the resin directly onto the fabric before autoclaving.

Testing had been made more efﬁcient with toggle clamps. These clamps ensured that
all specimens were clamped at the same points and with the same pressures. The
pneumatic rebound arrestor eliminated the need to catch the crosshead after it rebounded
from the specimens. The load cell could be calibrated before more specimens were
tested. Static calibration should be adequate, but dynamic calibration using a shock tube
or other dynamic method would be better. Quasi-static loading does not accurately
simulate the loading experienced during impact events.

The design of the tup should change for all future testing when penetration and

perforation thresholds are being sought. The sides of the tup should not be able to rub on

68

R3.2 3/4-14 UNC

R25 025.4
— I
* f {/ P—ﬁ_ — T f N
V — \

 

 

012.7 07.6

 

 

 

 

 

 

 

T
1 T __ " ‘ K)
Thickness L ‘J L
ofspecimen_d 6.4 —- p— 12.7 19.1

 

 

-#—— 50.8 ————-
Figure 6-1 : Proposed tup design.

the specimens and cause absorbed energy to be measured after the specimens are

perforated. The proposed tup design shown in Figure 6-1 would greatly reduce the

friction between the sides of the tup and the specimens. The tip of the top should be the

only portion that would contact the specimens. The tup would need to be hardened to

prevent deformation and damage to its surface.

The autoclave could be instrumented with thermocouples to ensure that all plates were
being cured with the same temperature. The curing of six panels at a time should be
abandoned if the temperature is not uniform in the autoclave.

The software currently used with the instrumented drop weight tester is DOS based.
All data recorded by the software had to be saved to a 3.5” disk then transferred to a
computer running Microsoﬁ Windows. Upgrading the software and computer so that
data collection and subsequent analysis could be performed on the same machine would
increase testing efﬁciency.

This study has revealed that more testing of the 3D woven fabric would be useful.
Numerical analysis of the 3D weaving geometry could be used to understand better the

behavior of the composite specimens during impact.

69

Appendices

70

Appendix A

Optical microscope images of cross sections of L[(0/90)5], SRO/90M, 2D[(0/90)5], and

3D|(0/90)6] specimens taken at a magnification of 120X

7l

    

qua m-

Figure A-l: Cross section of L[(0/90)5| specimen.

 

Figure A-2: Cross section of SRO/90);] specimen.

72

    

Figure A-3: Cross section of ZD|(0/90)5] specimen.

 

73

Appendix B

MATLAB program for calculating absorbed energy and impact energy

74

clear all

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% This program is written for English units (ft, 1b, 8) %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%Import EXCEL data first '...' is file name. Second '...' is worksheet
name
data = xlsread('fullrawdatalubetest.xls', 'test6');

%Groups each column of data each with a different name
Point_Number = data(:,1);

Time = data(:,2)/1000;

Load = data(:,3);

Deflection = data(:,4)/12;

Velocity = data(:,5);

Energy = data(:,6);

%The Dynatup head weighs 11.0862 pounds. This is correct. Weighed in
Composites Center 2/04.
Mass = 11.0862/32.1740;

%Store point called zero_velocity which is velocity when tup impacts
plate
1:0;
for(i=1:1ength(Time));
if(Time(i)==0):
1=l+1;
zero_velocity(l) = Velocity(i);
end
end

Newgacceleration = Load/Mass;
%Two methods for calculating the velocity difference using cumtrapz and

polyarea
Velocity_difference = cumtrapz(Time, Newgacceleration);

Velocity_differencel max(Velocity_difference)
Velocity_differencez = polyarea(Time, New_acce1eration)
%Ca1culates the tup velocity at each increment
for(i=1:length(Velocity_difference));

New_velocity(i) = (Velocity_difference(i)—zero_velocity)*-1;
end

%Calcu1ates the displacement of the tup
New_disp1acement = cumtrapz(Time, Newgvelocity);

%Two methods for calculating the absorbed energy using cumtrapz and
polyarea
absorbed_energy = cumtrapz(New_disp1acement, Load);

New;absorbed_energy_ftlb = max(absorbed_energy)

Absorbed_energy1 = polyarea(New_disp1acement', Load)

75

%Ca1culate the impact energy with and without mgh'
New_kinetic_energy_ftlb = .5*Mass*zero_velocity.‘2

New_kinetic_energy_w;mgh_ftlb = .S*Mass*zero_velocity.‘2 +
Mass*32.174*max(New_displacement)

%Output the total deflection
Total_displacement_inches = max(New_displacement)*12

%Simpson's rule for calculating integral of New_acceleration*d(Time)
n = (Time(length(Time),1) - Time(1,1))/(Time(2,1));
width = Time(length(Time),1) - Time(1,1);
for i=2:.S*n+1
y(i)= New;acceleration(2*(i-1));
end

for j=2:.5*n
z(j)= New_acceleration((2*j)-1);
end

Simpson_area_velocity = (width)*((New_acce1eration(1,1) + 4*sum(y)
+ 2*sum(z) + New_acce1eration(length(Time),1))/(3*n))

%Simpson's rule for calculating integral of New_velocity*d(Time)
New_veloc = New;velocity';
p = (Time(length(Time),1) - Time(1,1))/(Time(2,1));
width = Time(1ength(Time),1) — Time(1,1);
for i=2:.5*p+1
y(i)= New;veloc(2*(i-1));
end

for j=2:.5*p
z(j)= New_veloc((2*j)-1);
end

Simpson_area_displacement = ((width)*((New_veloc(1,1) + 4*sum(y) +
2*sum(z) + New_veloc(length(Time),1))/(3*p)))*12

%Plots

figure(l)

plot(Time, Newgacceleration)
xlabel('Time (s)')
ylabe1('Acceleration (ft/s‘2)')
title('Acceleration vs. Time')

figure(2)

plot(Time, New_velocity)
xlabel('Time (s)')
ylabel('Velocity (ft/s)')
title('Velocity vs. Time')

figure(3)

plot(Time, New_displacement*12)
xlabel('Time (s)')
ylabe1('Displacement (in)')
title('Displacement vs. Time')

76

figure(4)
plot(New;displacement*12, Load)
xlabe1('Displacement (in)')
ylabel('Load (lbf)')
title('Load vs. Displacement')

77

Appendix C

Load cell calibration data

78

 

g Puﬂyncjyprnm jug Calibration Data

 

 

 

 

é ..
é
.. Q 4
a :3 ~
3 1
|
In 10.0 2110 no 4&0 50.0
1111’ LOAN 1b ) *10H2
Tup Product No.: 8496-01 Maximum Tup Capacity: 5000 lbs 22241 N
Serial No.: 07645 Operator: Ray Smith
Approval: Customer: Michigan State University
Dynatup Job No.: 196771 Date: July 31, 2000

Bridge Resistances
A-E 861 Ohms A-B 641 Ohms A-D 645 Ohms
E-B 645 Ohms E-D 645 Ohms B-D 861 Ohms
Gage Pair Balance
(A-E, B-D) 0 Ohms (A-B, ED) 4 Ohms (A-D, ED) 0 Ohms

Collective Balance 50mV Test
(A-B, E-B, A-D, E-D) 4 Ohms 10 mV
Temperature at Calibration 73.6 degrees F. 23.1 degrees C.

Calibration is traceable to NlST; NVLAP #105023-0

Tup Calibration Factor Load Range
33261b 14749 N 1000 lb 4448 N
3327 lb 14799 N 2000 lb 8896 N
3326 lb 14749 N 3000 lb 13344 N
3322 lb 14776 N 4000 lb 17792 N
3320 lb 14768 N 5000 lb 22241 N

Figure 01: Load-cell calibration data

79

Appendix D

Load-deflection curves and energy profiles of laminated specimens

80

5000

 

4500
4000
3500
3000

Load,N

1500
1000
500

-500

2500 ,
2000 ,

 

 

 

Figure D-l:

 

1O 15 30

Deflection, mm
Load-deﬂection curves of L[(0/7.5)6| specimens.

20

 

Absorbed Energy, J

 

 

 

29

Figure D-2:

 

1 1 1 1 l 1 1

3132 33 34 35 36 37 38 3

Impact Energy, J
Energy profile of L[(0/7.5)6] specimens.

30 9 40 41

81

Table D-l: Data for L[(0/7.5)d specimens.

 

 

 

 

 

 

 

 

 

 

 

Software Results Veloci 7 Based Correction Method Extended Method
Specimen Tupl Ei (.1) Ea (J) h'(mm) Ei (J) Ea (J) Ei-Ea (.1) 1" (mm) Ei (J) Ea(J)Ih'(mm}
1 Rb 35.09 34.83 8.38 35.76 34.83 0.93 13.63 35.73 35.29 13.30
*2 Rb 36.42 36.30 9.40 37.13 36.30 0.84 14.48 37.08 36.04 13.70
*3 Pr 36.58 36.82 23.37 37.24 34.30 2.93 13.31 37.23 34.29 13.30
*4 Pr 36.99 37.16 23.37 37.69 35.25 2.44 14.22 37.98 36.74 16.30
*5 F_’n 37.50 38.11 14.73 38.22 37.42 (LL30 14.48 38.22 37.57 14.90
6 Pr 39.94__4_0.72 18.54 40.63 35.93 4.70 13.89 4059 34.92 13.50
*Average 36.87 37.10 37.57 35.82 317.63 36.16
6000
5500
5000
4500
4000
2 3500
1," 3000
8 2500
-' 2000
1500
1000
500
O 7
-500

 

 

 

 

 

Figure D-3:

5

 

 

 

 

 

 

10

15

82

 

 

 

 

 

20

Deflection, mm
Load-deﬂection curves of L[(0/15)5] specimens.

25

 

30

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

41
40 ———
_, 39 ________ _ —— ~
,1 38 -2 / — — _
2’ 37 —~— - — 1
g 1
o / 7 8
c 36 . __ __
“J / 4
1, 35 / ~ —- ——
g 34 __.__ / -. l -r
o 33 —
m /
a 32 —~——~~- ———-—~ -
< / 3.
31 ww —
30 JP 1 e 2 r5 ___- ___
29 l l l 7 I 1 . l l l 1 1
29 30 31 32 33 34 35 36 37 38 39 40 41
Impact Energy, J
Figure D-4: Energy proﬁle of L[(0/15)5] specimens.
Table D-2: Data for L[(0/15)6] specimens.

Software Results Veloci rBased Correction Method Extended Method
SpecimeJTupl Ei (J) Ea (J) h'(mm) Ei (J) Ea (J) Ei-Ea (.1) h'(mm) E, (J) Ea (J) 11' (mm)
1 Rb 35.10 29.16 4.06 35.67 29.16 6.51 11.53 - - -

2 _Bb 35.86 29.37 4.57 36.42 29.37 7.05 11.33 - - -
3 Rb 36.55 31.33 5.33 37.16 31.33 5.83 12.32 37.15 37.15 12.40
*4 RD 36.44 35.92 7.11 37.04 35.92 1.12 12.01 36.99 35.39 11.30
5 Rb 37.05 29.87 4.32 37.62 29.87 7.75 11.40 - - -
6 Pr 36.93 37.79 18.54 37.50 33.76 3.74 11.43 37.59 32.15 10.70
*7 Br 37.72 38.09 12.70 38.32 36.74 1.58 12.19 38.28 35.06 11.50
8 Pr 40.16 412.80 14.99 49.73 36.86 3.87 11.63 40.73 37.10 12.00
" Average 37.08 37.01 37.68 36.33 37.64 35.23

 

 

 

 

 

 

 

 

 

 

 

83

 

 

 

 

 

8000
7500

 

7000

 

6500
6000
5500
5000
4500
4000
3500
3000
2500
2000
1500
1000

500

-500

Load,N

10

15 20

Deflection, mm
Figure D-S: Load-deflection curves of L[(0/30)5] specimens.

41

 

 

40 —

 

39-e

 

38 4w—

 

 

37 T
36 -1r--———-——
35
34 —
33 ___.—-1”,

 

32 ~—~---—--—- ——
31 ~<

 

Absorbed Energy, J

 

30 -~——- - --
29 2-2.. / .________
28 -2.

 

 

27 l T l l l I l

f l l

l

T

 

27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

Impact Energy, J
Figure D-6: Energy profile of L[(0/30)5] specimens.

84

Table D-3:

    

 

 

 

 

Load, N
8
8
1
1
1
1
1
1
1

 

 

 

 

 

 

0 5 1O 15 20 25 30

Deflection, mm
Figure D-7: Load-deﬂection curves of L[(0/45)6] specimens.

85

41

 

40

 

 

39 smuuu-
38«m~w+—~

 

37 »—-~ew—

 

 

36-w~—w~_m~
35 +-
34 +w-~

 

33
32 w~-u
31 »—~—

Absorbed Energy, J

 

30 4~«u
29 T l l l l

 

 

 

29 30 31 32 33 34

. Impact

l T l l l 1

35 36 37 38 39 40 41
Energy,J

Figure D-8: Energy profile of L[(0/45)6] specimens.

Table D-4: Data for L

 

T E; (J)
33.92

41

35.
35.81
36.47

33.38
35.
.55

35.06
35.

86

11.
11.79
11.
11.1
11.81
11.68

Ea (J) 15,-Ea (J 11' (mm) E, (J)

.55
35.88
36.05
36.25
36.43
37.10

 

6500
6000
5500
5000
4500 -
4000 4
3500
3000
2500
2000
1500
1000
500

 

 

 

 

 

 

 

 

 

 

 

 

 

Load, N

 

 

 

 

 

 

 

 

 

 

-500 l l I l l

 

Deflection, mm
Figure D-9: Load-deflection curves of L[(0/90)6] specimens.

 

 

 

 

Absorbed Energy, J

one:
-sna
l
1
e
N
|

 

/ m TAM—"m— 8—4

29 30 31 32 33 34 35 36 37 38 39 40 41

Impact Energy, J
Figure D-10: Energy profile of ”(O/90);] specimens.

 

 

 

 

87

Table D-S: Data for L

 

T E; (.1) Ea (.1) WW" Ei (.1) (J) Ei-Ea( h'(mm Ei (J) (J) (mm
. . 1 - - -
1 1 . . 10. - - -

. . 7
11.68 7.11

88

Appendix E

Load-deflection curves and energy profile of stitched specimens

89

 

Load,N

 

 

 

Deflection, mm
Load-deﬂection curves of S[(0/90)6] specimens.

Figure E-l:

 

 

 

Absorbed Energy, J

 

 

l l

29 30 3132 33 34 35 36 37 38 3

Impact Energy, J

Figure E-2: Energy proﬁle of S[(0/90)5] specimens.

90

 

940 41

Table E-l: Data for S|g0/90)5| spgimens.
ftware Results Veloci l ased rrection Methodl Extended Method

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

91

 

 

SpecimeanupIEiU) Ea (J) h'(mm)] Ei(J) Ea(J) 15,-Ea (J) h'(mmll E, (.1) Ea (J) h'(mm)
1 ﬂ 35.02 34.63 11.94 35.58 34.63 0.96 11.43 35.82 36.32 12.40
2 Rb 35.86 34.90 7.62 38.42 34.90 1.52 11.35 36.49 37.29 12.40
3 Rb 36.20 34.48 6.86 36.75 34.48 2.27 11.07 36.82 38.75 12.70
4 Pr 38.35 37.31 19.81 36.91 35.25 1.66 11.43 37.09 35.27 11.70
*5 Rb 37.14 36.44 7.87 37.73 36.44 1.29 12.10 37.77 38.48 13.10
*6 Rb 37.65 37.60 8.13 38.24 37.60 0.64 11.86 38.25 38.45 12.30
*7 Pr 38.10 38.97 18.80 38.70 38.61 2.09 12.19 38.69 36.64 12.40
8 Pr 40.01 41.15 25.40 40.60 36.34 4.26 11.94 40.62 36.45 12.50
'Average 37.63 1_'37.67 38.22 36.88 38.24 37.85

 

 

Appendix F

Load-deflection curves and energy proﬁle of two-dimensional woven specimens

92

6500

 

6000 1

5500 +7~—
5000 1

4500 ~

4000 «7 »- .5
:5 3500 + .

3000 a
2500 ~
2000 —
1500

1000 » ¥~

 

 

 

500
-500

 

 

 

Figure F-l:

10 15

Deflection, mm
Load-deﬂection curves of 2D[(0/90)6] specimens.

 

Absorbed Energy, J

 

 

 

4.

 

 

 

29

Figure F-2:

 

l T l 1

30 3132 33 34 35 36 37 3

Impact Energy, J
Energy proﬁle of 2D[(0/90)6] specimens.

8 39 40 41

93

Table F-l: Data for 2D

T

Ei(J) Ea (J) h'(mm Ei (J) Ea (J) Ei-Ea (.1) h'(mm E, (.1)
33.99 33.50 7.7 . 1. 11. 34.58

. . . . .22
35.35 35.86 11. 0. 11.79 35.95

. . . . .1 11. .52
36. 7.47 21. 37.11 34.33 11.35 .11
. 1 . . .61 . 1. .25

94

 

Appendix G

Load-deﬂection curves and energy profiles of three-dimensional woven specimens

95

Load,N

 

0 5 1O 15 20 25 30

Deflection, mm
Figure G—l: Load-deﬂection curves of 3D[10/15)6| specimens.

 

 

 

Absorbed Energy, J

 

26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

Impact Energy, J
Figure G-2: Energy proﬁle of 3D[(0/15)6] specimens.

96

Table G-l: Data for

  

Specimen (J)

(J)

(n EA»

 

Load,N
00
01
O
O
1

 

Figure G—3:

 

 

 

 

 

 

 

 

 

 

 

10 15 20

Deﬂecﬁon,nun

Load-deﬂection curves of 3D[(0/30)6| specimens.

97

Absorbed Energy, J

 

41

 

40

are——

38~
37eem—M.

36

35»_4—~
34+“

33

32 1’

31
30

 

 

29

 

1.

 

 

l

l

l

l

I

l

T

l

l

29 30 31 32 33 34 35 36 37 38
Impact Energy, J

39 40 41

Figure G-4: Energy profile of 3D[(0/30)5] specimens.

 

Table G—2: Data for 3D|gOl3025| specimens.
Software Results Veloci 1 Based Correction Method] Extended Method

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

98

 

 

 

 

Specimen Tu Ei (J) Ea (J) 1" (mmll Ei (J) Ea (.1) Ei-Ea (J) 1" (mmll Ei (J) 5.0) h' (mm)
1 Rb 35.14 31.62 4.83 35.66 31.62 4.04 10.41 35.63 35.01 10.20
*2 Pn 35.94 35.02 9.14 36.49 35.02 1.46 10.99 36.47 36.52 11.00
*3 Pn 36.39 36.21 10.16 36.97 36.21 0.76 11.78 36.89 34.73 10.40
4 Pr 36.84 37.72 18.03 37.41 33.35 4.06 11.68 37.29 28.04 9.40
5 Pr 37.18 37.73 12.95 37.70 34.17 3.53 10.57 37.67 33.58 10.30
'6 _fr 37.54 38.11 12.535 38.08 35.43 2.65 10.80 38.05 34.92 10.50
7 Pr 40.01 41.56‘ 33.78 40.51 32.23 8.28 10.03 4g._47__31.88 9.60

, ‘Average 36.62 36.45 37.18 35.55 37.14 35.39

 

 

 

 

 

Load,N

 

 

0 5 10 15 20 25 30

Deflection, mm
Figure G-5: Load-deflection curves of 3D[(0/45)6] specimens.

41
40

 

 

Absorbed Energy, J
(.0
A

2

 

28 29 30 31 32 33 34 35 36 37 38 39 40 41

Impact Energy, J
Figure G-6: Energy proﬁle of 3D[(0/45)6] specimens.

99

Table G-3:

  

Specimen

 

 

 

 

 

 

 

 

O 5 10 15 20 25 30

Deflection, mm
Figure G-7: Load-deﬂection curves of 3D[(0/90)6] specimens.

Absorbed Energy, J

Table G-4: Data for 3D

Specimen T

1

41

 

 

40 --
39

 

38

37v«_——~+
36 ...m ,

35
34
33 ~»
32

 

31
30 1///

 

 

29 1

29 30 31 32 33 34 35 36 37 38 39 40 41

Impact Energy, J
Figure G—8: Energy proﬁle of 3D[(0/90)6] specimens.

.57 33.

101

 

Ei (.1) Ea(J) h'(mm Ei(J) 153(0) Ei-Ea (J) 11'1"“ Ei (J) Ea (J) h'(mm
34.06 33.

10.40 34.56 34.63 10.

.1 1 .
1 1 .
11.

11.1
11.

 

 

Appendix H

Laminated specimen damage

102

#5 l #6
38.22 J 40.63 J

 

Figure H-l: Top view of damage to L[(0/7.5)5| specimens.

103

#5 . 1 #6
38.22 J 40.63 J
Figure H-Z: Bottom view of damage to L[(0/7.5)6] specimens.

 

 

Figure H-3: Top view of damage to L[(0/15)6] specimens.

105

 

Figure H-4: Bottom view of damage to L|(0/15)6| specimens.

106

 

Figure H-S: Top view of damage to L[(0/30)6| specimens.

107

 

Figure H-6: Bottom view of damage to L[(0/30)6] specimens.

108

 

Figure H-7: Top view of damage to ”(o/45).] specimens.

109

 

Figure H-8: Bottom view of damage to L[(0/45)6] specimens.

110

 

Figure H-9: Top view of damage to L[(0/90)6| specimens.

111

#7
37.10 J
Figure H-10: Bottom view of damage to L[(0/90)6] specimens.

 

112

Appendix I

Stitched specimen damage

113

 

#8
40.60 J

Figure I-l Top viw of damage to S[(0/90)6| specimens.

114

#7

#8
38.70J

40.60 J i
Figure l-2: Bottom view of damage to S [(0/90M specimens. I

 

115

 

Appendix J

Two-dimensional woven specimen damage

116

Fi

40.82 J
gure J-lzTop view of damage to 2D[

ll7

 

(0/90)(.l specimens.

 

 

——-‘ern.-7<-3-g;W——
l
.1

 

Figure J-2: Bottom view of damage to 2D[(0/90)6] specimens.

118

Appendix K

Three-dimensional woven specimen damage

119

#7
37.10]

Figure K-l: Top view of damage to 3D[(0/15)¢] specimens.

 

120

 

Figure K-2: Bottom view of damage to 3D|10l15)¢] specimens.

121

 

40.51 J
Figure K-3: Top view of damage to 3D[10/30)6] specimens.

122

 

Figure K-4: Bottom view of damage to 3D|(0/30)5] specimens.

123

 

#7
36.99 .1

Figure K-S:

40.63 J
Top view of damage to 3D[10/45)6] specimens.

124

#7
36.99 J

Figure K-6: Bottom view of damage to 3D[(0/45)6] specimens.

 

125

#6
37.48 J

#7
38.15J

Figure K-7: Top view of damage to 3D|(0/90)5| specimens.

 

126

#7
38.15J

Figure K-8: Bottom view of damage to 3D[(0/90)5] specimens.

 

127

References

128

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Kim, J .K., Sham, M.L., “Impact and Delamination Failure of Woven-Fabric
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Sutherland, L., Scares, C., “Effects of Laminate Thickness and Reinforcement
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Liu, D., “Delamination Resistance in Stitched and Unstitched Composite Plates
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