—_ —— —_ —— — —— —_ —— —-—I —— —— —— _— —— —— — 102 812 THS AN é J‘s-’ES’HGAWON OF THE EfifiFA57-ABSORBMG QiiAUTIES OF VAREOUS CUSHEONENG MATERIALS Thesis for #110 Degree cf M. A. MIQHIGAN STATE‘ UMWERSI‘VY Rage: H. Barr $59 2‘:- if; "M f‘\ r I .fi‘ ' ‘3 7 i a! ! V“: j {I r " i n J I. \L’; V " '1 It“. ‘i i F» . 1 f no r MSU LIBRARIES “ r [if N r ”r n I E L, , l L. I b x {E 2' 1h; ”- x, . n; 3% r I I ,1 - I fl. ,. RETURNING MATERIALS: P1ace in book drop to remove this checkout from your record. FINES will be charged if book is returned after the date stamped below. AN INVESTIGATION 01" m IMPACT-ABSORBIN} QUALITIES OF VARIOUS GUS HIONIM} MA'IERIAIS ROGER H. BORE. tms Suhnitted to the College of Education of Michigan State University of Agriculture an! Applied Soieme in partial fflfillmmt of 'the requirement. for the degree of MASTER OF ARTS Department of Health. Physical Education and Recreation 1959 BUREAU OF EDUCATBONAL RESEARMH COLLEGE. OF EDUCATION MsCmuAN suns umvtxsiw EAST wsmo. MICHlGAN ‘umv"‘” "" " ' Acmmm The writer wishes to show his appreciation to Dr. Henry J. Hontoye who helped design the experiment and whose valuable criticien made this paper possible. R.H.B. 'p r \\'/ *1}! .3" {i Q; MAI EHML IN BACK OF BOOK TABIEOFCONTENTS CHAPTER - PAGE I. THEIROBIEM...................... l Statemntoftheproblem.............. Importanceofthestuw.. ..... Limitations of the problem. . . . . . . . . . . . . II. REVIEJCFTHEIIMATURE............... Effectsofimpact................. Cushionimuaterialteste............. BO ONONUtl-‘H CDShRODWMtOrmB-ooo-coo-0000000 memeSOmeUREeeeeeeeeeeeeeeeee13 t3 Expr meat “3 ad 0 O O O O O O O O O O O O O O O O O Ci ExperinentelDeeign................ Ivassums ..... .17 Immotabeorption.................1? Fatigueteet....................21 V. SW.CONCLUSIONSANDRWATIONS . . . . . . . 2h Smry......................2lb Conclusions....................25 Recommdatione..................25 BIBIIWRAPHI.........................27 APENJIX A - Recordings on Oscilloeoope. . . . . . . . . . . . 29 iii FIG“ LISTOFFIGURES Percentage comparisons - Football Head and Spinal Injuries Direct Fatalities. 19147-1958. . . . . . . . Comparison of Impact Characteristics of All Cushion- im Materials at Various Velocities. . . . . . . . . Conparison of the Impact Characteristics of the Ten Beatcmhmmmternl.e e e e e e e e e e e e e e Comparison of Fatigue of Cushioning Materials. . . . iv PAGE 18 19 22 TAKE 1. 2. LIST OF TAKES PAGE Direct Fatalities: . Specific Locations of Injuries... 7 Analysis of Variance Tables of Cushionim Materials atVariousVelooities. . . . . ... . . . . . . . . .20 Fatigue Test Variance Table . . . . . . . . . . . . . 23 CHAPTERI THEPROBLEH During the past twenty-seven years there has been a steady in- crease in the number of fatal head injuries in football. Although the helmet 'nanuraoturers realise this startling fact. it is shocking when one considers the clan amount of research that has been done in this area. Various cushioning materials are used as liners in football helmets today. largely because of their cushioning appearance and with- out a thorough knowledge of their impact-absorbing qualities. mm It was the purpose of this study to measure the acceleration of cushionng materials and their recovery aspect when struck by an object. This was accomplished by striking each material at various velocities and by repeated blows . . W Realizing the imrease of fatal head injuries in football it is obvious that research is greatly needed in this area. This problem is not a new one. In Marvin A. Stevens' book. mm gm m (1933) helnet resdesigning was already being considered because of the increasing head injuries. There was a tendency at that time to make headguarde heavier.larger and harder in an attempt to cut down on the imreasing head injuries. The result was that they merely became offensive weapons and failed to absorb the shock of blows.1 Since that time helmet construction has progressed considerably but it is evident by statistical proof. that helnet construction has not kept pace with the speed of the game.2 The Twenty-Seventh Annual Survey of Football Fatalities (1931- 1958) states that fatalities directly related to football have averaged 17.52 per year, and a total of I473 deaths have been recorded since 1931.3 The report further shows that a tabulation of specific location of fatal injuries has been perfoned by this committee since 19%. and that the head and face areas accounted for 63.80 percent of all fatal- ities. the spine for 17.68 percent. ard abdominal-internal for 18.62 percent.“ A further analysis of the data by the location of the blow reveals that spine injuries were caused by blows to the top of the head. Con- bining these two (head and spine) results in the face that 81.l&8 percent of all fatalities since 1914? are due to traumatic blows to the head.5 (See Figure 1.) In a still closer investigation. the specific location of each blow. was reported. The results were: 1Marvin A. Stevens. m gm of mm]. mm (New York: A. S. Barnes and Co.. 1933). p. 63. 2Committee on Injuries and Fatalities. American Football Coaches Association. Dr. Floyd R. Eastwood. Chairman. W m flame: of. W W. January 1959. p. 3. 3m” P- 3' “m" p. 30 51mm” p. 12. FIGURE 1 Percentage Comparisons" Head and Spinal Injuries Direct Fatalities (1937-1953) PERCENTRGE 78% Vk‘.‘ 76% ' _- 'M' “IL \ 721 WT?!" ! 70% if" ”A?“ 7" r‘ 68$?" ~. : i _. .5 law we ”+9 '50 '51‘ '52 '53 '54 '55 '56 '5T‘58 *Cunulative Averages based on all fatalities reported yearly since 1931. The left and right front and side of the head incur 21.32 percent of all injuries. Internal injuries rank second with 18.62 percent. Blows to the top of the head (resulting in spinal injuries incur 17.68 percent. Traumatic blows to the back of the head incur 13.21 percent of all injuries. (Interpreted this means that the most hazardous areas of the body are ranked: (1) both sides and front of the head. (2) ingernal organs. (3) top of the head std. (it) back of the head). As a result of. these startling figures continued research is of absolute necessity in this area. that qualities comprise the best and safest helmet have not yet been determined but more ant! more research is being carried on in this area. In a letter sent by Dr. Lombard to Dr. Floyd Eastwood in June of 1956. he states his ideas on helmet construction: A hard external shell capable of deflecting blows because of its smooth surface and capable of distributing the blow because of its resistance to distortion. An energ absorption layer next to the helmet skull. an! internal. of not less than 1/2 inch thickness. A resilient sisim layer or a sling )lutband suspension layer to attenuate the uncomfortable impacts. Since that time. however. little researchhas been carried on to determine the best qualities which compose a good impact-absorbim helnet. Some research has been done on football equipment at the Cornell Aeronautical Laboratory. Inc. Various other studies have been done by the Aercmedical laboratory. School of Medicine of Southern California. Los Argeles; Lombard. et al.; an! several Master's thesis have been written on the subject. A‘ 6M. . p. 1+. 7Protection. Incorporation. Division I’- O. Box 61037. South Station. Los Angeles 61. California. Personal correspondence dated February 9 a 1959 . It is hoped through this study on cushionim materials. a contri- bution can be made to this great need. and the groundwork can be established to find a suitable material. which will help in the reduc- tion of head injuries. through its excellent impact-absorbim qualities. W This research is primarily to test the impact-absorbing qualities of various cushioning materials. One should realize that even though a material can absorb impact at high velocities there are other factors not undertaken in this test. which must be considered. Temps rature is an important factor. Football equipment is used under many types of weather conditions; therefore. the material should be effective under all temperature conditions. Another factor to be considered is the proper thickness of the material. At what thickness will the material be most effective? This study is just a part of the necessary research needed in this area. No final conclusions can be drawn until all available material has been thoroughly investigated and all factors considered. CHAPTER II KEVIN or TIE IITERATIRE The review of the literature is divided into three sections. Firstly. the effects of impact on the human head; secondly.‘cushionim material tests; and thirdly. a section on the qualities of cushioning mat srials . W medical doctors have a great responsibility in football. If a player is rerdered unconscious by a blow to the head. in most cases the player will recover before the doctor examines him. Although he recovers should he be allowed to continue in the contest? This is the decision the doctor faces. Most‘medical‘ doctors. however, do not realize the fact that the largest percent of fatalities in football are due to head injuries. (See Table l) N In the Nutty-Seventh Annual Survey of Football Fatalities (1931- 1958) it was revealed that fatal accidents have resulted from traumatic blows to the head in 72.25 percent of all injuries.8 The percentage of total fatal head and spine'injuries. due to blows to the head. has increased continually since they were first recorded in 190. (See Figure 1e) - 8committee on Injuries and Fatalities of the American ‘Pootball Coaches Association. WM Annual Earn: a: mm W. on. 5:11.. p. 11. .Aamaa ease enov x00: on» no masons) ocean on» no onsaasu maHuseo one: o» soap oHuasseuye .SmH 5 octet e3 eeHBeeo- .3 d .33 beacon. inflamed dug «a g Aug 3533 .320 68393 .m 9»on ..5 .coaamaooeed eonoeoo HflspvoOh.cooHnul< .nouaaaepem use neHnanH no eeuaHEsou1eenoom 8.9: 8H H HH oHH on 3 3:8 NHld . e o 1 o N N o elooae pea 3.3 Hm H H mH n a Heats; 8.H u o H H o o .5383 yea 86H Hm o m S a. N at. .55 £3 .25 Hearse 83m Hmdm mm o a em e S 3833.. so: mm. H o o o o H .eeec Be one: HNAH mm o H H o _ m veer co oBee mod 5H o H HH m m 23.73:... 96 nH o o HH H H e 33.83 8% e o o m o H 23.. scope :H.~ a o o H o M £3 sooth mm. H o o o o H eases send one: .u H38 HeHloo euoHHoo Hooeom 9E Harm poHEem boom so seem HHepoooe sea as one a; emmmHuSmH motor—H no 5383 3288 eeSHHepea 22.3 Hades When the head receives a hard blow. it is possible for the following to happen. (1) the skull can be fractured, (2) the brain can be injured. by the force being transmitted through the skull causim a concussion. or (3) both can happen.9 Denny-Brown and Russell10 experimentally produced concussion in animals by striking their heads with pendulums of different masses. Their results proved there were no concussion effects with the lighter pendulum as lorg as the head was fixed but when it was allowed to move as little as 3 mm. a concussion occurred. Holbourn11 in another study on concussions investigated the physical mechanism of brain injury. Holbourn used artificial brain sections of gelatin framed in a paraffin-wax "skull". He found that the maximal strain was produced in the temporal region as a result of rota- tional accelerations applied to the "skull”. This was because the rotating "skull' exerted its strongest force on the brain at the point where the temporal lobe was gripped by the lesser wing of the spenoid. He concluded that the main causes of head injuries were: (1) deformation of the skull with or without skull fracture. an! (2) sudden rotation of the head which is probably responsible for concussion. Lombard. e3. 31. .12 designed an experiment to determine the'limits 9Edward R. Nye. "Protecting the Head from Impact-Injuries" U.S. Rubber Co. . Hishawaka. Indiana. Personal correspondence dated December 10. 1958. p. 8. 10D. Dem-Brown. and H. Ritchie Russell. "Experimntal Cerebral Concussion". m. September 19'41. p. 93. 11A. Holbourn. mechanics of Head Injuries.‘ m. October 9. 191‘3e {30 “'38. 1"zcharles F. Lombard. et a1.. "Voluntary Tolerance of the Human to Impact Accelerations of the Head" m1 9.; 513.33.19.11 Mam. April 1951. p. 111. of acceleration that a human would voluntarily tolerate. when struck on the head. A pendulum of a mass approximately equal to the head and headgear was used in this study and within its steel head was mounted a strain gauge type accelerometer which was capable of measuring in excess of 500 g. The output from the accelerometer was amplified and fed directly to a cathode-ray oscilloscOpe tube. The face of the oscilloscope was photographed by a 35 mm. streak camera. For an analysis of the records obtained the 35 nun. films were put into a modified microfilm projector. The results of these experiments showed that the limit of linear acceleration which the human can tolerate voluntarily. by being hit on the head was not reached when blows as high as 38 G were recorded. The subjects. however. withdrew from higher energy impacts because of bruis- ing. tension loads on the ligaments of the neck muscles. or sharp burning pains in the joints of the cervical vertebrae. The results of these and other eacperimnts show a definite need for more work to be done in this area. since the majority of deaths to mechanical force in work or play are caused by head injuries. Men of all fields can contribute for a common purpose. W The Inland Manufacturing Co.. of Dayton. Ohio. participated in a round robin test sponsored by the Society of Plastics Industry to establish a standard test to measure resiliency in plastic materials. The Ball-Drop Resillience Test as it was called. consisted of dropping a 5/8 in. diameter steel ball. from an 18 in. height on a piece of material and measuring the rebound of the steel ball. The apparatus 10 consisted of an 18.111. vertical. clear plastic tube. into which a 5/8 in. diameter steel ball was released by an electromagnet. Circles on the tube aided in the visual recording of the ball rebound. The Ball- Drop Resilience iscalculated as follows:13 -W Ball Drop Resilience_ 18 in. at 10C“; Lombard gt. 51.5” developed an apparatus to provide dynamic load test data. It consisted of a large block on which the test speci- men was attached and a perdulum type hammer containing a strain gauge accelerometer was mounted. The pendulum was released from different heights. thereby striking the material at various velocities. The out- put from the accelerometer was fed to an oscilloscope which as operated without a sweeping motion. A 35 m. camera recorded the height of the pip of the oscilloscope. C. S. Wilkinson15 of the Goodyear Tire an! Rubber 00.. developed an electronic pendulum for evaluating the impact absorption of foam materials. The purpose of this study was to reassure various foam mater- ials for shock and vibration characteristics. This was done by measuring the deceleration of a physical pendulum. The machine was designed to simulate: the conditions present when a person's head strikes the safety pad during an auto collision. Keeping this in mind the shape of the 13Inland Manufacturing Division. General Motors Corporation. Dayton 1. Ohio. Personal correspondence. dated January 11*. 1959. 1"""Nerw Helmet Protection Theory Advanced” (Reprinted from 41mm. January 21». 1918. 15c. s. Wilkinson. "Electronic Pendulum for Evaluating Impact Absorption of Foam Materials” 3mm. September 195?. p. 8&1. 11 pendulum used was hemispherical. The design was very flexible. however. to allow different size bobs to be substituted. Impact velocities were in the range of 10 miles per hour. The mechanical design of the machine consisted of a support which was constructed of heavy steel. The pendu- lum‘was made of aluminum.and was attached to the lower end of a shaft built up of two thin-walled aluminum tubes h8 inches long. Using two tubes prevented the perdulum from being twisted. The upper end of the tubes was fastened to an.ax1e. which rotated in ball bearings. A strain. gauge accelerometer was fastened to the back side of the pendulum to indicate deceleration upon impact. The signal from the game was amplified to a dual-beam Tektronix oscilloscope. The penetration of the pendulum into the material.was indicated by a transducer built especially for this purpose. After the material_had been fastened to the base of support the pendulum was lifted to the proper height and released. Upon impact. the electrical impulses from the transducer were relayed to the oscilloscope. These traces along with the decelera- tion traces were photographed with a Polaroid type camera to obtain a permanent record. ghahlaninzaflsiaziala. Cornell Aeronautical Laboratory. Inc.. has done considerable research of cushioning materials. for protecting the head against in; flicted blows of various velocities. The results of their tests indi- cate that the materials which performed the best were the materials having (1) low density. (2) high energy absorbing characteristics. (3) resistance to deformation and (h) adequate thickness.16 16Nye. Edward 11.. an. m” p. 10. Density represents the weight of the cushioning material per unit volume. and is usually expressed in pounds per cubic foot. Materials are classified as either energy storing or energy absorbing. Energy storing material is any material which has complete rapid recovery after impact. Energy absorbirg materials are those materials which are permanently deformed when struck. Most of the energy absorbing materials unfortunately are good for one blow and have to be replaced.” An ideal material should have a very low resistance rate. It should be thick enough however. to prevent the head from "bottoming' under the impact.18 173211.. p. 10. 1mm'o p0 10° CHAPTER III METHODS OF PROCEDURES This chapter is divided into two parts: (1) an explanation of the equipment used in the study. and (2) the design of the experiment. W A strong wooden block was constructed on which the various cush- ioning materials were attached. This block was connected by two steel cables fastened to the ceiling. and was free to move when struck by an object. The weight of the wooden block was nineteen and three quarter pounds. A perdulum type weight whose mes was five and thirteen-hurdredths pounds was used to strike the cushioning mterials. This weight was also attached to the ceiling by means of two steel cables. The striking part of the pendulum consisted of a flat surface. The pendulum was held at various positions by an electrical re- leaSe. This consisted of a magnetic coil in which the pendulum type weight was inserted. This coil was turned on and off whenever desired. A small chain. connected to the release bout. ran tlrough two pulleys and was fastened with rings to a fixed point; on the wall. The acceleromter used in this study was a Schaevits limar accelerometer. It was mounted inside the wooden block to record the peak acceleration of the block upon impact. The output of the accelerometer was fed into a Hewlett-Packard Model 130A oscilloscOpe. Mounted on the face of the oscilloscope was a Polaroid camera which photographed the output as it appeared on the scope face. The beam was stepped at various posit ions on the scape face. making it possible to photograph eight impacts on one photo. When the velocity was increased. it was sonatimes necessaryto decrease the sensitivity to keep the height of the pip from going off the screen. A linear relationship existed between the height of each pip and the sensitivity setting. thus. as the millivolts per centimeter increased. the height of the pip decreased. Twenty-two materials were used in this study. Some of the mater- ials tested are already widely used in athletic equipment. The thickness of the materials were tested as close to once-inch as possible. Half- inch materials were doubled when tested. The following material were tested: Wm N24 demw oxfiuuHmowaNnm> Rubatex Division Rubateu: Division Rubatex Division Rubatex Division 0.3. Rubber Co. 0.8. Rubber Co. Firestone Rubber Firestone Rubber Dayton Rubber 00. Dayton Rubber Co. Dryden Rubber Co. Dryden Rubber Co. Dryden Rubber Co. Rubber Fabrics Co. Kopprs Co.. Inc. Xoppers Co. . Inc. Koppers Co.. Inc. Koppers Co.. Inc. Blockstrom Co. Blockstrom Co. Blockstrom Co. Dow Chemical Co. W 6.200.C R-300.V R-313-V R.310-V Ensolite AI. Ensolite H Neop‘sne Slab Foamex Slab 8-120 M 8-620 200-570 200-555 250-632 (unknown) Polystyrene 1 1b. density 2 lbs dam ity 3 lb. density Lt 1b. dons 1w Paratea: inner laced Paratex fins Paratex IV Polyethylene 313mm 1 1/8 in. 1 in. 1 in. 1 1/8 in. 9/16 in. 1/2 in. 1 in. 1 3/16 in. 1 in. 1 in. 1 in. 1 in. 1 1/16 in. 1]“ in. l in. l in. l in. 1 in. l/2 in. l in. 1 in. 1 1/2 in. 15 Hereafter throughout the paper. the materials will be referred to by their code numbers. W The 1+“ x 4" samples of materials were fastened to the wooden block by rubber bards. Each material was tested twice at the following velocities: six. nine. twelve and fifteen feet per second. A fatigue test was also made to determine the effects of repeated blows on the ten best materials previously tested. This was done by hitting a sample of each material eighty times. 0 Every tenth blow was recorded and photographed. ‘ Calibration of the accelerometer was made by recording the differ- erence in levels between the signals when the accelerometer (mounted inside the wooden block) was rotated from a neutral position to one in which the face of the wooden block is parallel to the ground then to one in which the back side becomes parallel to the groutd. The difference between the two recordings is equivalent to two times the acceleration of gravity (2 G). This was done before every testing period. The center of gravity of the wooden block was determined by run- ning a plumb line from one of two attached corners while the opposite corners were unattached and drawing a line where the string fall. This was done for both sides. Where the plumb lines crossed indicated where the center of gravity fell. It was necessary to find the center of percussion of the wooden block in order to prevent the block from twisting if hit at some other point. The center of percussion was found to be very close to the center of gravity. as was expected. The mass moment of inertia about the point 16 of attachment had to first be determined. This was done as follows: T=2fr /h_2_ T periodsofpendulumin g r seconds. ceiling. g g gravity. therefore: r 3 distance from attachment to center of gravity of block. k2 . 1&2; k g mas mommt of inertia about points of attachment at The following formula was used for determining the center of percussion: attachment to center of percussion. 8 a la g : distance from point of r g 3 8.62 feet The center of percussion in our particular case fell above the center of gravity. Normally it should fall below. This was probably due to the difficulty in determining the true pendulum period and because the cables were not directly connected to the ceilirg but slanted outward. After the materials were tested the recordings were treasured and were transferred to gravity units. (See Appendix) The results of the two tests are shown by graphs. The accelera- tion in G was plotted agaimt velocity in feet per second in the first test. In the fatigue test the acceleration in G was plotted against the number of hits at fifteen feet per second. CHAPTR IV THE RESULTS This chapter is divided into two parts: (1) the results of the impact-absorption test, and (2) the results of the fatigue test. Wan A total of twenty-two materials were tested in the intact absorp- tion test. Each material was hit twice at the following velocities: six. nine. twelve and fifteen feet per second. The mean of the two tests was used for graphing the results. (See I"igures 2 and 3.) In Figure 2 all twenty—two materials are compared through the use of three graphs, thereby giving a clearer picture of the results. In Figure 3 the ten best materials from the impact-absorption test were selected and compared. As shown by the graphs the peak acceleration of the block increases as the velocity is increased. on all materials. This is to be eJCpected. The Analysis of Variance technique was enployed to_ determine whether the difference between materials at all four velocities was significant. At all velocities a significant differeme was found to exist. (See Table 2.) The within-groups variance estimate was used as the denominator to determine the 1“ ratio and is referred to as the error variance. This was used to test the significance of the cushioning materials at four velocities . Haven .3... week 5 hfiooaob 18 \5’ ma «H m m mm- «H m; -..m ma «H a m _ _ ‘1 .... ~ i . . a \ ., \ . a. \ M. , - . - l M s l x t t . \ ON w... .. l x, ‘\ \\ - .\ .. . A R \ xxx. . . . ..L .H x x a _ o: ‘\.\\x \w x a ..x. l .... H ... x \ . 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ANALYSIS (F VARIANCE TAR-ES OF CUSHIONING HAW AT VARIOUS VELOCITIES 20 (Velocity 6 Feet Per Second) sumac: sun or sun at VARIANCE ESTIMATE Between 3 .392 . 51+ 21 161.55 11mm: 41.11..“ 41mm 311511.455 a fi (Velocity 9 Feet Per Second) SOURCE sun or 301111111:T df VARIANCE mmrs Between 313211.37 21 1191.611 , w t 108.111 22 £1.92 ' 3;.h33,5§ #3 - _1 (Velocity 12 Feet Per Secorfl) SCURCE sun or SQUARES] df VARIANCE ESTIMATE Between 125.3“9.25 21 5969.01 111mm; 1135.73 22 491%.... M 125 ages 1+ (Velocity 15 Feet Per Second) amnes- v SUM OF SQUARRsl df VARIANCE mm Between 213,000.74 21 10,142.89 wit 0 1_.....__2.;I...2§_..._._.T Tom 1. L1 ‘ 1'35“.” F = 303.18 1" B 301.31 F = “61.116 a"'I‘wenty--one degrees of freedom exists in the between. source because of the insertion of missing data at those veloc ities . 21 We: The ten best materials selected from the impact absorption test were used in the fatigue study. These materials included both energy absorbing and energy storing tutorials. A The energy storing materials were hit at fifteen feet per second impacts. at one minute intervals. for a total of eighty blows. Host of the energy absorbing materials broke after forty blcws. therefore. testing was discontinued at that stage. (See Figure ’4.) This test was also repeated and the mean was calculated for graphing. From the figures one can observe that materials. D. X. and Y are the best three of the previously selected ten. The Analysis of Variance technique was employed between these three materials to deter- mine the following: (1) if the difference in fatigue of these materials was significant. (2) if the materials differed significantly among them- selves in relation to fatigue. (3) to determine if the interaction be- tween the three materials and fatigue is significant. In all three cases the F ratios were highly significant. (See ; Table 3.) The wit bin-group variance estimate was used as the denominator to determine the 1" ratio and is referred to as the error variance. This was used to test the significance of the differences between the three cushioning mterials. ard the fatigue rate among themselves. 1§ Eeeem new seen ma ea 23:. 523$ an end: no non-ea 22 98lo on oxroeomoeomoaoaa .. n . a q .1 A e a q q a . Ill 1 \ Ali ...\0l\\\.1\1\.11.-1 1 a 11 1 - - - --M11111 1 \ Kill. 1- 11“ 11111111 1 1.1...”1111n1111 H11 1111\\ ,., l d lii| I! i I Kl Dir 1111!! I- \\ ... I. r 1111 11|I111111 _ 11 e. an. I] l .x K II. 1\ . . .A\ V I1 ..,\ \x \ \\ I. \1 \\ \\ i! / 1 i 9.39334 buns-um 11 ”3.85 Beam ages eszoEnB no ”BE: no zonHfieso : one»; 9 u'; uoneaetaoov L1 1 23 TABLE 3 FATIGUE TEST VARIANCE TABLE W souncs SUM OF SQUARES df VARIANCE ESTIMATE Fatigue 1.111018 8 138.90 r 3 19021 Material 268.25 2 1311.13 ‘ F a 18.55 Interaction 3.I+53.27 16 215.83 1“ a: 29.85 Iniividual . difference w 209. 39 #1 1w 5.0%.;2 55 __ W CHAPTERV SUI-MARY . CONCLUSIONS AND RWIDATIONS Ema: It was the purpose of this study to measure the impact character- istics of various cushioning materials when struck by an object and to test their recovery aspect. This was accomplished by striking each material at various velocities. ami by repeated blows at a fixed velo- city. Two tests were perfomed on the cushioning materials. An impact absorption test. on twenty-two materials was accomplished by hittim each material twice at the following four velocities: six. nine. twelve. and fifteen feet per second. In testing the materials for fatigue. only the ten best from the impact absorption test were used. Each piece was hit at fifteen feet per second. at one minute intervals for a total of eighty hits. Every tenth hit was recorded. The cushioning naterial was attached to a wooden block. Inside the wooden block an accelerometer was mounted. The acceleration upon impact was transmitted to an oscilloscope. On the oscilloscope was mounted a Polaroid canera'which photographed the peak acceleration. The results of both studies were shown by graphs givirg an over- all comparison of the various materials. The Analysis of Variance technique was employed in both tests to determine if the results were significant. 25 W 1. A review of the literature indicates that the sides of the head incur the greatest percent of head injuries. therefore. they must be adequately protected. This can be accomplished by using the proper kind and amount ofcushioning material. and leaving more space for absorbing the blow. f 2. Material Y, X. D and B are shown by this test to be the best materials for use as padditg in football “helmets. , 3. Some of the best cushioning mterials showirg low acceleration under one bloat. have a very high fatigue rate. therefore. of little value in football equipment. 1+. Various cushioning materials used at the present time as padding in football helmets do not have good impact abscrbirg character- istics. Wives. 1. Cushioning materials should be tested under different types of temperature conditions. 2. The fatigue test should be studied in such a way to determine at exactly what point the cushioning materials ”break down". 3. In testing cushioning tutorials it is recommended that they be of uniform thickness. 1:. The thicknesses of the cushioning materials should be varied to see if there is a correlation betwaen performance and conditions. 5. Cushioning materials should be tested more than twice urder the same conditions. 6. The pendulum head should be changed in shape to detemine how i 26 well the material will perform.under'different type blows. 7. An accelerometer should be mounted on the pendulum to determine the correlation of the acceleration of the wooden.blcck and the deceleration of the perdulum. BIBIIMRAPHI 28' BIBLIOGRAPHY Comittee on Injuries and Fatalities. American Football Coaches Associa- tion. Dr. Floyd R. Eastiood. Chairmm WW émex of W W- January 1958. Committee on Injuries and Fatalities. American Football Coaches Associa- tion. Dr. Floyd R. Eastwood. Chaizman. WM m at 129.1211 We January 1959. Denny-Brown, D.. and W. Ritchie Russell. "Experimental Cerebral Concus- sion." mm. September 1941. . Holbourn. A.H.S.. "Mechanics of Head Injuries." m. September 1941. Inland Manufacturing Division. General Motors Corporation. Dayton 1. Ohio. Personal correspondence dated January 14. 1959. Johnston. D. H. ”For Safer Football Research at Cornell Aeronautical Laboratory." Egg lack {Lima W. October 23. 1955. Lombard. Charles F. . e_t_ 1].. ”Voluntary Tolerance of the Human to Impact Accelerations of the Head.” The Jamal of Austins Housing. April 1951. . McPhee. H.R. "Doctor Looks at Football Hazards.” m 2m. October 195“. "New Helmet Protection Thea'y Advanced.” mm M. January 21*. 19.139. Nye. Edward R. "Protecting the Head from Impact Injuries.‘ U.S. Rubber Co.. Ensolite Products Department. Mishawaka, Indiana. Personal corresporrience dated December 10. 1958. Protection. Incorporation. P.O. Boat 61307. South Station. Los Ameles. California. Personal correspondence dated February 9. 1959. Rawlins. J .3. "Design of Crash Helmets,“ 133921. October 6, 1956. Stevens. Marvin A. The Central at. fastball WI. New York= A-A. Barnes and Co.. 1933. Wilkinson. 0.3. “Electronic Pendulum for Evaluating Impact Absorption of Foam Materials.” Rubber, m. September 1957. APPENDIX {'20 mm an on em mm mm NM 3 _m .n 11o.“ o. a 2. on.” ed 2. d GM ofiuilfifl .. mfl .. 11a a a we? 8...... on 2. 2d 33. owilrounm . .2 e u n 1.21. 1-1 «of and a Li the new 2% flow . a .. H n a all.» qufi r axed one or.“ one on...“ new . N a m~ n a 2....» am: om 2. «We «a... a 2mm .. HI .. a e no 2...? do 2. «9 no... 32 «3 . a. . n '21111111 wfid~ «.... r gJWN uh... N; o; . w e a -.. maiden d a one 2...... mud on“. 313 n a 8 3 o. t . 0sfifi1§1lfifl i". um. 11%4 gal; «fird a “T a x e. s 1. V we Sade 21. in. an. WW. $4113. .. .2 .. x ._ 1:... 1.1 .1 and oi. on .3 8. a... E1 e. .. a . x o 2 1.. l are «no r 3.811qu E.» can. owning m ail.“ x 2 m_ _ . a. ._ M . 3.2. g 2. n1 16$ oer 8.: oo.» . ml . Q ._ o H enema 11% .5. «@1113; d3 2... .. A. . u o 2 a _ 31% 4:. OH. a . 00.. a r e U N. __ I H 3% new .1. on one .... «ea 3% Tu 1.: u __ o. o. |.. 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