RELATIVE ENERGY ABSORPTION PROPERTIES OF FREE AND ENCLOSED CUSHIONS “19515 for ”19 Degree OI M. S. MICHIGAN STATE UNIVERSITY Karl Snow Willson 1958 I IIlIIII!TIMIIII!IIIIIIIIIIIHIIIIUIIIll 3 1293 10613 8534 RIIL’ITIVE IEII‘IgRGY ABILCRJTIC‘N I'R-‘l'LIRTISS OP FETCIE AILD 32:01:03.3!) CUSLIIC-XS By Karl Snow Willaon AN ABSTR CT Submitted to the College of Agriculture of Michigan State University of Agriculturo and Agilied Science in partial fulfillment of the recuiremonta for the degree of HAJTSR OF SCIiNCE Dep9rtment of Forest Products 1958 This study was initiated to evoluote sons of the differences in the verformence of package cushions under test c nditione and in practice. The standard tests which are used for detsnnining cushion performance properties are performed with cushions canpressed between two parallel platens. In use, however, cushions are restrained by containers which prevent lateral dofornition under pressure and trap air within the cushions. These conditions were believed to hove a nonsurnble effect on energy absorption properties, and this difference was studied. The materials used for the tests were Hairflsx Grades II, III, IV, and 8, s connercial brand of latex-bonded animal hair. Static compression tests were made on cushions between parallel platens, end on cushions in an enclosure. The energy absorbed by the cushions was deternincd from force-deflection curves and compared. DJnsnic tests were conducted under similar conditions and the results cowpsred as cushion factor- etress curves. A definite increase in the stiffness of cushions was found to result from the lateral restraint in the stntic tests and from both lstorel restraint and air trn;;ed in the cushion by the dynamic test platen. 0n the basis of these results, it is roconncndod that cushion design factor tests, both static and dynunic, be conducted on a more realistic bnsis. The use of cushion factor curves for design purfioscs must be reconsidered. Surgestions ere node for modifiestions of onckoge design to utilize the full capabilities of cushions, and several lines of investigation which should increase the understanding of cushion performance are rccasscndod. RELATIVE EELSIEY ABAfJ'i-H‘TICI‘I F3131: LIRT‘ILJS CF I"; .33 AID EIE-‘L‘LCbLSD CULJLIIC’Z‘IS By Karl Snow Willeon A TLESSIS Submitted to the Collers of Agriculture of Yiehigsn State Univwrsity of Agriculture and Av lied Science in partial fulfillment of the rcquirenents for the dearee of “(5) 2. a “m n, A“ I .mm s A! ‘0‘...“ ‘4: 4C .JJO‘JJJ Departnent of Forest Eroducts 1958 Q3 (\‘N r- ‘— x I} u I \l 1‘ -‘-.CK'.':CT .fsz7G-JJ '. $133 . The writer wishes to exprere his sincere agprecietion to Jr. Robert E. Kinble and the Arwour Cushioning Products Divisiun for assistance and the furnishing of materials for this study. Thanks are due Dr. Jenee Goff and Dr. Harold Raphael of the Michigan State University School of Packaging, and Dr. John Turk and Er. Richard Hexson of the Glues Container Unnufncturers' Institute for suggestions end discussions regarding this project. Finally, the writer is grateful to his wife for her assistance and enceurngenent. ii 31.0 K: FC 23' L ”Di: :21"; QITS 0 LIST OF FIGU.JS o INTROjUCTICH a c o B iCKGRC‘UHD o o o 0 PL“! 0' STUDl o - STATIC TEST3 o o o TRBLBG e o o o GRAfHS . c o o DYNAKIC TESTS o o GRAPES o o o a TRELJS 0 o o 0 G33: KL CCNCLUEIUUS RSCQE'-Z£-I$ID’..TIGNJ o 5’33 -JI‘ IONS FOR F U 735i LIST CF RJFERETICJS 2.1"? .IJDIX I: APEdHDIX II: :25"! O O O O O O O O O O O O C I Q C O O O O O C O O O O :S'I'UDI 33 Ar groxx III: cusnxox 93:1 cuav;s AflfifiDIK IV! Af{lRATU5 4: \v Ltd iii ' it} OF CCL-é'I‘L'JI-ETJ CALIBRATION 0F DYING-{EC (H a)..- 0 EYJJRGY CILGULWICJ-IS FDR STATIC TLZS’IS uga CF éTATIC 33:33! ABLORFTICN DAT FOR cusfixeu DESIGN 0.. NITH ovonICN FCCTOR 1C X-fi-i 3A .3 URI; 35 P :1 go 11 Nam 12 27 54 A} as 59 60 61 67 111311;:me v: Paar-03:21) nmnovnm-zrs IN DYI-IA‘EIC T154? IIJJTRUIQIQTAJLION . . . . . . . . . . . ”.68 APP-3531K VI! ADUITIOZML 3.3-50'1‘13 33131336.} CH iv FIG‘J'RS l. 2. LIST CF 13153338 CV‘JT. LVII .a' CF B L?) I'f T34": ‘73 RICE-ZINC} UEJJD F03 T‘T‘l‘. TIC CC)’ -1 .MJICJN FLsz 0 o o o o o o o o CLO?) 3UP 0F BELOW 7-7 TEJTINC? 2’}. 31.1"”, S C JFK} .uICLJ..JrR..: in) CC... . 1:3 1-; 11.4.0.2-.. o o o o o c o o DYN’LZIC BRO» TICITZR o o o o o o o o o o o o a “V7” IC TQLITJR IT‘S'?RTC'TI'I ”JUICY” U... ‘n‘ BI 03?: DI‘KSE’C’C’? CF UYIJALIC TKLTI‘JG CIICUI'I'S o o 'T‘YEICRL SPECCH ‘u'f-VC 1"ii(}TC:C Ri'xf‘l‘iS I’C'i F1133 CUJEZICN’ rd 5" E ’1" C" P- I" ( C K U TY ICwL SHOCK 1-17.17“; i‘::‘CT(J.G C'J‘JiiIOII-Seeooooooocon-cocoon BLCCE’ DI 133.52! OF ER ICSIED ""‘3'rI“"I"I3 . . . in \ __.n L: A U! (,1) m ‘\ 1" ‘ O 41 42 69 In! T RC DUO TI {31" The savornl test methods which have evolved for the dfiterninption of cushion design characteristics all involve forces voting upon a cushion which is at rest and unrestrained. In static tests for energy obsorgtions, the cushions are compressed between two platens and a lend-doflection curve drown. Dynamic tests, whether for determination of energy absorption or a Cushion Factor, also involve placing an unrestrained cushion against a platen while a movnble :lnton in impacted upon it. These test methods introduce a certain element of error into the design factor determinations. In packaging practice, cushions arc customarily enclosed within a container which introduces additional factors into the situation. Cushion friction against the sides of the container retards the load motion. “his effect will Vary with the nnturo and density of the cushioning material, and with the cnoothnsss of the enclosing surface. Confining of the cushion also prevents normal bulging of the stressed cushion, and increases its efnoctivc stiffness. Entrny ed air within the cushion is a major factor in changing cushion yroycrtiea. Bozo air is congresscd under the pinton and trapped within the Cushion during the bricf duration of the shock even in dynamic tests with free cushions. When the cushion is enclosed on five sides, with the novnble platen making the sixth side, the closed system uses the trapped air as an additional cushion. The air also adds a danping effect to the cysts , reducixg rebounds. Trooped sir introduces little, if any, changes in the static test results, since the loading rate is slow enough to perwit escnpe of all of the air. materials, such as 8036 plostic fears, having I closed cell structure, will not show major trapped air effects since the internal air is permanently enclosed. Restriction of lateral expansion may be nore significwnt, as internal co pression is limited by the internal pressure developed under stress. This study is intended to establish some of the relationships between testing Conditions and actual use conditions for cushioning materials, and to make recomtendstions for design data corrections and further investig"tions. BATKGRCUKD In packsging applications, cert in yroperties of cushioning materials must be known to permit the design of cushioned packages by other than trial-end-error methods. The most common date are load-deflection curves, stress-energy curves, and cushion factor curves. Static loading tests are e widely-used method of conpering cushioning materials. One method is to derive a curve of load 23: coepression from a nechincdmnde force-disglecement curve. This load-compression curve can be used as a design curve, telling what deflectinn n cushion will undergo at a given load. The load—compression curve can also be used to obtain a are h of stress zg, thickness of cushioning to use. The mexinum stress which will be applied to a cushion is found by nultiplying the static stress by the "g-fsctor", or the number of tines the force of gravity the packaged object can withstcnd. (l) The totel energy absorbed by the cushions in the nbove is represented by the area under the curves. The 'g-fwctor' which an object can withstand depends on the most fragile pert of the object or groduct. It is defined as the ratio of the eccclerction received by an object to the accelerntion due to gravity. In p cknging sgylicetions, _tho 'g-fnctor' is a measure of th deceleration received by e prckpfie when it stops suddenly as it strikes a floor, wall, or other solid obstacle. The decelerntien must be ejusl to the acceleration the package roco1Vea as it falls, or the weight multigllod by the acceleration duo to gravity. Tho 'g-foctor“ is nlso known as the fragility index, denoted bV,?. Another method of ajplying force-displaccoont curves to design probloma is to prepare stress-energy curves, or a pair of atress-strnin and strain-energy curves. The energy ahsorbod by a cushion can tuen be found if the stress which it receives is known. It is also necessary in Bone instances to know the deflection that will result under a static load, such an stocking in a warehouse. The elementary stress-displacement curvo will rcvorl how much load can be ay;1lod to a package without crus log it enough to damage the contents. Dotcrtinatlon of dynamic energy absorption properties is accomplished by several methods, all using sinilor ar-arotus and calculutlons. Ono apparatus uses a drop hwwaer with a stjlus attached, giving charts of both the dro ring distance of the hammer and its penetration into the ouohion. (l) A more efficient method of finding tno energy uses acceleronotors and electronic op arntus to measure the chock imparted by a known force to a cushion. This method may yield either energy absorption curves or cushion factor curves, both of which are directly agfilicablo to cushion design. The cushion factor is a dimensionlos" fiuantity which is used as a crmgutntionol device to singlify cushion dcaigns. The cushion factor varies with the force-energy ratio, and is plotted against stress. The cushion factor is onual to o 43/8)“me x t=Gt/h, where r is the force, E is the energy, W is the load weight, G is the 'g-fuctor', h is the drop height, and t is the cushion thickness. The cushion factor is thus essily determined if the factor G can be measured. The stress is determined simultaneously with the cushion factor, and is eouel to WG/l, where W is the weight of the inp cting platen,.A is the area of the platen, and G is the deceleration. A stress-cushion factor curve nornslly has a minimum point, at which stress the cushioning material is most efficient. The thickness of cushioning required for a given application in deternined by rearranging the above cushion factor equation to t ='Ch/G. Use of these cushion design properties is demonstrated in appendices II and III. ELAN CF LT"DY In order to investigate some of the differiltial effects between cushion tests and performance under use conditions, tests were conducted on sevcrcl c;shions by both static and ynsnic methods. Container conditions were simulated by a wooden enclosure for the cushions under test. The static torts produced forcordcflection curves, which were used to draw up stress-strain and strain-energy curves. The total energy absorbed in the tests was coqpnred. Dynamic tests were run to dotcnxine the fragility index G of the cushion for a known stress. The cushion factor was computed from G and cougnrntive cushion foctor~stress curves drawn.. The moterisls used for these tests were four grades of rubberized hair, known commercially cs Hairflex Types II, III, IV, and 3. This material consists of curled animal hairs coated end bonded into molded shapes by latex rubber. The density of the noterisl incr~ssos with increasing tyge numbers. The sscplos used for these tests were rectangular blocks, 12 inches square and o noninnl two inches thick, except for the No. 8, which use in 10-inch sounros. It was n‘t posSible to condition the test Speoisens prior to use, but it is felt that the nature of the material minimized any variations due to changes in moisture content. STATIC TSJTS Force-deflection cuers were obtained by conrreaeing the cushions between the platens of a Baldwin-Exory 50,300 pound, FG7-SH-#, Universal Tooting chhlne, using a 0-1030 pound range. This machine is equigpod with a deflectometor and 10nd rwcordor to produce direct force-deflection curves. Cushions used in the initial test series were prostressed by compressing them to loss than 50% of their nominal thicknes- for ten cycles, and then resting than for about 1/2 hour before testing. The loading rate was one inch per minute for both prestrossing and for tooting. Tests of free cushions wore Made b, oox;ressing tho egeciwone between two 12-inch-squaro platens to a thickqeaa of about 0.4 inch. The tests were started with he spacing between the platens equal to the two~inch nominal thickness. of the cushions. Th 3 introduced a small initial load to the opncicons, but compensates for the non-uniform actual thickness of the epociwena by giving a uniform initial thick- ness. Inacnmch as theac are rolntive tosto, such errors will not affect the uvofulnosa of those data for ccmgorativo purposes. To sinulot“ the conditions present when a cushion is :1 cod in a closed container, on enclosuro was constructod of fi/h-inch glywood. This enclosure was just over twolvo inches square, just clearing the sidos of the :1oton, and two FIGURE 1 OVERALL VIEW OF BALWIN mm MACHINE USED FOR STATIC OGIPRESSIW TE'I‘S inches deep. Cushions were tested by piecing them in the fixture, centerine the plnten, and com rescing the cushions into the enclosure. The tests were started with the glatens two inches apart, mrintaining the conditions of the free cushion tests. The forces recorded at 0.1-inch increments of deflection were averaged and entered into the energy computation sheets. The other factors were com uted by the method of Appendix I, and stress-strain, strain-energy curves plotted for each set of test conditions. As a check of the effects of prestressing the test cushions, tests were ale an using new cushions with no preworking prior to testing. The comparative total energy absorptions for the static tests are given in Table I, and illustrated in Graphs 1-7 (pnges 27 - 55). There is a definite increase in the energy absorption at a given stress, for each material, when enclosed, except for the decrease in absorption in the prestressed Trpe IV cushions. The reason for this difference in performance 13 unknown. The increase in absorbed energy indicates that the cushion has a greater stiffness, and transmits wore energy to the article \T is intended to protect. There is e greater incronse in absorbed energy with the enclosure for cushions which heve been prestrossed. This is a result of a higher strain in the prestressed cushions, which is peraitted by the loosening of internql bonds in the cushion FIGURE 2 CLOSEUP G" BAWIN TESTING MACHINE, SHOWING ENCLOSURE AND CUSHION IN PLACE. DEFLEOTCMETER IS SHO‘N IN RIGHT FORMROUND 10 during prestreesing. The energy absorption at a given stress is not elwnyl increased by the enclosure, since the stress does not very directly with the deflection. here force must be exerted on an enclosed cushion to produce e desired deflection, demonstrating that the enclosed cushion is definitely stiffer and offers more rec stance to the cmnprecsing yleten. There is some effect in these tests due to friction between the edges of the cushion and the solid enclosure. This effect will be least with the lower-density materials, but the loose nature of the materiel should make this error negligible in proportion to the additional stiffness doc to restraint of lateral motion in the congressed cushions. The relatively slow loading rate end the ole rnnce between the platen end enclosure render any additional energy due to entrapped air negligible. ll OG-ZPARISON OF TOTAL ENERGY ABSORBZD TABLE 1 IN STATIC CGEPRS‘SSION T4318 CUSHION STMSS AT TOTAL mac! CHANGE IN ENERGY ENCLOSURE 1.6' DEFLECTIOR A$ORBSD ABSORBED BI ENCLOSED CUSHION GRADE 11 ‘Paasmessen f Fm 1098 13.8.1. o§619o u‘lbfl/inb Enclond 2.08 , 591%)“ 'f 953 GRADE III PRESTRESSED Fra. 5.20 .58580 311010.“ 505) 064965 ‘f‘ 11% f GRADE 11141510? 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E: N.” 8mm.“ ommn. 03. mo. 23 mm. 0% «A 334 Ram. .26 mo. 93 cm. 0% o.“ mmfié man. $3 mo. 36 3. 3m m6 8%. meow. 23 mo. 33 3. cm: n6 R8. mas. 3A 8. man mm. m: 3 2a. was. 3..“ mo. mum on. man 06 ER. 092. 3.~ mo. Spa mm. SN m6 m3. m8“. B.~ mo. 5....“ 8.. 4%.. 4.0 8.2. 2.8. a." mo. 2.4 mu. m: n6 28. mama. no; mo. a." 2. 9.: «.o mas. mas. an. mo. t... mo. 2. a6 Rama: :5 “Mme: “Mu-mm Aduxuzuac “me Afiflbzma: Afioflv «momma? 38. a 53: £53m 5.: 8% 8a .a 8.5 .353 ammodfi 8588... En uflfim mu an I l l i/ 0'“ / _ me Cushions / “n“ Enclosed cushions // "" _ 0.35 —°" ‘4 0.3 " "' 0.25 fa: --1 \ "‘ n 0.2 :3 .é E *- “ 0.15 g ._ “Ab-.1 b— —0.05 I l l l 0.5 1.0 1.5 2.0 2.5 smsss (pal) (mm 1 COMPARATIVE S’l‘RBSSqENERGY CURVES GRADE 11 011311101515, 313515255531) 27 I I I W —— Free Oushiéns / u" - Enclosed cushions / "" "o.6 — #0.; I— _'D.3 "' “—3.2 +3.. 1 l l o 1 2 3 h SIRESS (p51) (RAH-I2 oonpmnvx may cums m In wsmous, mssmssssn 28 ENERGY (hubs/1:9) .I I I “I“ —_ cushions ---- Encloud Cushions / L... "10.6 40.5 4on “DJ ~20.2 —001 ’ l l l o 1 2 3 h mass (ps1) mm 3 mum SW6! wavss mm: 111 means, nor 2225112353313 29 ENERGY (in—lbs/in3) j I 1.2 —‘ Free cushions """ Enclosed Cushions -- f‘ 1.0 F- — 0.6 —- "' 0.11 — ‘J 0.2 l J 0 2 I. 6 ° STRESS (p01) m h 'conpmnvn summer waves m H (muons, mssmsssen 30 may (mm/1:13) 1.11 I l I —— Free martian: ‘ "“ ‘ Enclosed Cushions I. "— —’102 __ _. 1.0 I-—- ‘— 0.8 Q E .é __ _ 0.6 g __ —-» 0.11 -- a 0.2 ’ 2L I ‘ J 0 O h 5 05 STRESS (psi) Graph 5 (DEPARATIVE S‘mBSS-BIIERGY GRVES (mm IV GISMONS , 1101' RESIRESSBD 31 l I I I Fr“ Cushions ----Enc108¢d momma ' / r. .— / I I I I 0 I. 8 12 16 20 STRESS (psi) mom 6 comma smug-Rev waves m 8 005111003, masmessan 32 3.0 2.5 1.0 1.5. ‘ 5 mm (mans/1:} )_ O 0 VI I I I I , ’“° . / "'— Prec Cushions ’ / -' "’" Enclosed Cushions // "" ' 3.5 "' 3.0 _ 2.5 __ ii 2.0 > 3 - 1.5% I—- 1.0 .._. fio.5 / - I I I I o 0 I; 8 12 16 20 STRESS (psi) GRAPH 7 mmuvn WY cums m 8 (1151110113, 1101‘ mnsmsssan 33 DYHAJIC TESTS Dynamic shock test: to determine the force in G’s absorbed by a cushion were run on the drop test ajparatue in the Michigan State University Pack ging Laboratory. The drop unit consists of a foot-square platen operating Vertically on two precision-ground supports. The glaten is guided by super-precision frictionless sleeve bonring of the recirculating ball type. The system has negligible friction losses when a heavy platen is used. The maximum ioeaible vertical travel in about 50 inches for the moving arm, and about 46 inches with the platen attached. The platen uaod had a deyth of about three inches to permit entry into the solid enclosure. The shock received by the platen on striking a cushion generates a current in a barium titannte crystal accelorometer. This current is amplified in a cathode follower amplifier, into an oscilloscope. The noise filter is necessary to remove signal static due to the movement of the bearings on the Vertical shafts. I In use, the voltage calibrator is used to feed a signal enuivolent to a knzwn number of G's into the oscilloscope for calibration purgocec. (500 Ag endix III). This signal can then be Cwnpared with the shock impulse to determine the shock strength. An audio oocillctor end a yuloe former were used to superimpoce n 530-cyclo blanking signal on the accelerometer signal, periitting a deterninction of the duration of the shock. An electronic decode counter was need to nonsure the frequency of the blanking signal so thot its accuracy could be maintained. The oscilloscope trace was recorded photogrnghijlly on I!) e Polaroid oscillogrngh camera. To get a clear ignnl, a fontoelectric cell was used to trihfivr a single sweep of the signal at tho tins of impact. With thdtocilloscopo screen scale c librnted for a known number of G's per division, t.e shook signal strength is easily read from the photogreyhs. For the dynnwic teste, a set of statically preetroosed cushions were tested one b, one under the platen falling from a measured height above the cushion. The gloten was then reset to a new height and the series of drops repented. cone compar- ative tests were made with cushions that had no yrior working. The noxinum shock r adings r suiting free these tests were averaged and recorded on the dntn shoots along with the pbtcn weight, drop height, cushion thickness, and cushion area The stress experienced by the cushion at maximum shock is computed fro: the relation F1: HG/A, where F is the stress in pounds per 'qunre inch, W is the drop heed weight in pounds, A is the platen fires in sruere inches, and G is the maximum chock recorded on the oscilloscope. The cushion factor is conyutsd free the defining equation C=:TG/H, where O is the cushion factor, which is dinenaionlcss, T is the cushion t ickncss, G is the shock, and H the height of the drop onto the cushion. This relation is derived fran the force-energy ratio of the impact to the thickness, 1.6., c=r/s x T=WGNH x T==G/H : T. Coogsrotive graphs were made up “letting stress 13, cushion factor for each test condition. The :ininun value of the cushion f ctor occurs at the stress where the cushion is most efficient. This con be seen b; solving the cushion factor equation for T, where T==fiC/C. The oininum thickness of cushion reouired in a given situation is thus grogortionsl to the cushion footer. In yrsctico, the stress con often be adjusted to the lowest cushion f ctor by changing the weight or sirfvce area of the puckfified article. The curves do not tench a niniiun value for the cushion fsctor within the stress rouge coVered, when the cushions are enclosed. For the grade II and III cushions, the free cushions bed a lower cushion factors throughout the stress range studied. This means that the use (3 free-cushion cushion f ctors for design yur;ooes gives insufficient protection in this stress range. The use of cushion fnctors deriVsd from tests in enclosures resuires thicker cushions to protect the article. The 56 cxglanation for thin 18 that the cushion is rendered consider- ably stiffer when air is tro}ped and the lateral deflection restricted, and the cushion therefore tr~nsnite a lfirger portion of the shock to the packaged article. This is in agreement with the static tests, where the enclosed cushions absorbed more energy because it could not be dissipated in lateral foiseon-t;po deformation. The tests with enclosed cushions also impert noticeably less rebound to the gluten. This is a further indiC¢tion that the cushion is absorbing a greater portion of tee energy on the initial inycct. This daqping effect can be attributed to th 9 feet th~t the cushion cannot deflect normally because of the trapped air. There is more latitude for equipment and Frocedurnl errors in the dynanic tests than in the stotic tests. Calibration of the electronic circuits is a particularly exacting task. Care must be taken to assure that the platen strikes wholly inside the encloaure. On low-level drops, striking the wells of the enclosure would give an erroneous reading which might not be apynrent. 57 FIGURE 5 DYNAMIC DROP TESTER, SHOWING 1311010ch (1), ACCELERGIETER (2), AND CATHODE FOLLOWER AMPLIFIER (5). momsm AND CUSHION ARE IN PLACE. DROP HEAD IS RAISED AND READY FOR RELEASE. 58 . ' .o- u'. '3’ l 4‘..-"' o‘ o. f. J£:I¥‘; . 8 FIGURE 4 DYNAMIC TESTER INSTRUMENTATION, SHOWING OSCILLATOR (1), PULSE FORMER (2), CATHODE FOLLOWER POWER SUPPLY (5), ELECTRONIC SWITCH (NOT IN USE) (A), VACUUM TUBE VOLTNETER (5) VOLTAGE CALIBRATOR (6), SINGLE SWEEP TRIP (7), NOISE FILTER (8), OSCILLOSCOPE (9), POLAROID CAMERA ATTACHMENT (10), AND PULSE COUNTER (11). HOOKUP IS SHOWN IN FIGURE 5. 59 18 G's .026 Sec. 19 G's .024 sec. FIGURE 6 DYNAMIC TESTS TYPICAL SHOCK WAVE PHOTOGRAPHS HAIRFLEX GRADE IV 12' DROP FREE CUSHION 41 l6 G's .028 sec. lk 6'3 0 028 803 o FIGURE 7 DYNAMIC TESTS . TYPICAL SHOCK HAVE PHOTOGRAPHS HAIRFLEX GRADE IV 12' DROP ENCLOSED CUSHION 58mg .maoefio 3 case EEG mmmfigobfi. .838 m E56 3.3 mmmfim 9n 3 - o.~ m; o.” 1 no A q _ _ _ 8230 3.38»: I .. .. 83.8 gill CUSHION FACTOR nummumummmm .maoaxmau Hun ma¢=u mmumwmumcpuam.-onmm=u muzmqmu “mung mmumuw C m.~ m.~ o.~ m.o . _ _ _ _ aa«:upo.eomo~uqu.u.u..1 nauguao .oym.nnun.. 11: i ;I II. L—— g 3 t— ‘1 2 '" " 1 __ Put Cushion -- _ “loud Cushion I I ' J l o 0 0.5 1.0 1.5 2.0 2.5 STRESS (psi) GRAPH 11 wsmon FACTOR-STRESS cmvss GRADE Iv CUSHIONS, PRESTRESSED L6 J— OJSHIOI PM I —‘ "' 2 L "" ‘ _ 1 ——Fre¢ Cushion _-"Encloscd Cushion l l l o 0 0.5 1.0 1.5 2.0 STRESS (psi) GRAB! 12 CUSHION FACTOR-STRESS CURVES GRADE Iv CUSHIONS, NOT IRESIRESSED A7 TABLE 16 STRESS-CUSHION F‘CTOR D5TA HAIRFLZX GRADE II FREE CUSHION, PRflSTRSDSED Cushion Thickness 2' Drop Head Weight 7 lbs. It oz. DROP AVERAGE STRESS CUSHION HEICNT MAXIMUM (lbs/inz) FACTOR 5 6 .3) h.0 6 7 .50 2.5 9 10 .55 2.2 12 1h .77 2.5 15 1a .90 2.4 18 21 1.15 ' 2.5 21 27 1.43 2.6 24 55 1.80 2.8 27 ~ 40 2.19 5.0 50 51 2.79 5.4 TEBLE 17 ST RiSS-C 35H ION FAG TC‘R DATE HAIRFLSK GR‘DE II ENCLOSED CUSHION, IRSSTRESSED - Cushion Thicknooo.2' Drop Head Height 7 lbs. 14 oz. DROP AV?R\GS STRJSS CJJHION EEICAT MAXIMUM (lbs/inz) FACTOR h -.22 2.7 5 6 7 .58 2.5 9 11 .60 2.h 12 12 .66 2.0 15 15 .32 2.0 18 13 .93 2-0 21 20 1.09 1.9 2h 23 1.26 1.9 27 25 21357 1.9 49 TALLL‘lB STREJ-S-CUSEIICE-i FUCTG‘R DATA HAIRFLLZA GR'DS III FREE CUSHION, ERLJTRJSAJD Cushion Thickness 2' Drop Head Weight 7 lbs. 14 02. DROP AVE: CE STRESS CUSHION HEIGHT AAIAIHUR (lbs/IAZ) FACTOR 5 h .22 2.7 6 7 .58 2.5 9 9 .49 ':.0 12 11 .60 1.5 15 15 .32 2.0 13 17 .9} 1.9 ab 26 11:42 2.2 27 51 1.70 2.5 f.) 0 9 A) IV C \J'l 50 57 50 TAIL” 1' l. ‘ ETRJLS-CUSH C3 FACTOR DOTA HAIRPLEX GRADE III ENCLCCLD CUCAION, EREoTRSJSiD Cushion Thickness 2" Drop Heed Weight 7 lbs. 14 02. DROP AVSR O3 2 2315 cu NICN HEIGHT MiKLiUA (lbO/in3) FACTOR 5 6 'vifi 4.0 6 11 .60 5.7 9 15 .71 2.9 12 19 1.0A 5.2 15 20 1.09 2.7 13 25 1.26 2.6 21 25 1.57 2.4 2h 27 1.43 2.5 27 50 1.64 R) u '9 \\fi H TAHLZ 2 STRE.’$3-L".’.LIL'IOH FACTOR DATA F1 iii-{FLEX GRADE. III FRJS CU NICE, NOT PRESTRSSSSD Cushion Thickness 2' Dre? Head Weight 7 lbs. 14 02. DROP ATER CE STRESS CUSHION HEIGHT HARRIET (lbs/1n2) WBTOR 5 5 .27 5.5 6 7 .58 2.5 9 9 .49 2.0 12 10 .55 1.7 15 15 .71 1.7 13 15 .82 1.7 21 18 .93 1.7 24 20 1.09 1.7 27 26 1.h2 1.9 50 29 1.59 1.9 TABLE 21 STRESS-CUSHION FICTCR D'2TA liAIEiFLJJK GR':D:$ III ZINCLC3ED CUSIEI N, NOT PRSSTREQLJSD Cushion Thickness 2' Drop Heed Weight 7 100. 1h 02. DROP AVSR CE CTRISS CUSHION HEIGHT RAAIAUN (IDs/1n2) FACTOR 5 5 .35:- ‘ 14.0 6 10 .55 5.5 9 14 .77 5.2 12 13 .93 5.0 15 21 1.15 2.8 18 22 1.20 ‘2.h 21 25 1.57 2.A 2h 27 1.43 2.5 27 ,29 1.59 2.1 50 29 1.59 1.9 55 STRIS-‘Js-CU ERICA"! F ZCTOR DATA HAIRFLZX GRADE IV FREE CUSHION, PRSJTRBJSSD Cushion Thickness 2' Drop Head weight 7 lbs. 14 02. DROP ‘ 1732103 STRRRI HEIGHT MIKIKUM (lbs/ina) 3 7 .58 6 8 2AA 9 10 ' 055‘ 12 15 .‘71 15 16 .88 18 19 1.0h 21 22 1.20 2h 24 1.51 27 23 1-55 50 51 1.70 \ GIMHI 0N F ACTO R h.7 2.7 2.2 2.2 2.1 2.1 ”2.0 2.1 2.1 DROP HEIGHT 5 6 9 12 15 18 21 221 27 50 T 'BL3 25 STRESS-CUSHION FACTOR DATA HAIRFLEX GRIDS IV :NCLCSID CUEHION, PRESERssssD Cushion Thickness 2' Drop Mend Weight 7 lbs. 14 oz. AVERAGE STRZJS CTSHICN RAIIEUN (Ibo/1A2) FACTOR 9 .49 6.0 15 .71 4.5 17 .95 5.8 20 1.09 5.5 21 1.51 5.2 26 1.42 2.9 . 50 1.60 2.9 53 1.00 . 2.0 55 1.30 L 2.21 58' I 2.03 2.5 TiBLE 2“ STRESS-CUSHION FACTOR DAT HAIRFLZK GRADE IV FREE CUSHIONS, NOT PRESTREISED Cushion Thicknooo 2' Drop Heed Weight 7 lbs. 14 oz. DROP AVARACE STRSJS CCCAICN HEIGHT 12.111221 (IDs/1n2 ) FACTOR 3 8 .44 5.5 6 11 .60 5.6 9 1h .77 5.1 12 1h .77 2.5 15 16 .88 2.1 18 15 1.0h 2.1 21 19 .93 1.7 2h 1. 1.20 1.8 27 2: 1.15 1.6 50 2A 1.h2 1.7 56 Taan 25 STRJSS-CKSEICW F‘CTCR DATA HflIRFLEK GaiDS Iv 3331101339 CUQHIC‘N, I‘ZCT IRIS :CRJQSLD Cushion Thickness 2“ Drop Head Height 7 lbs. 15 02% DROP gvggficz STRJSSr CUSHION HSIGHT HA£LE¢J (lbs/infi) 210703 5 1o .55 6.7 6 15 .82 5.0 9 22 1.20 h.9 12 20 1.09 5.3 15 25 ‘ 1.242 5.5 13 23 1.55 5-1 21 29 1.59 2.8 24 51 1.70 2.6 27 53 1.6h 2.2 30 52 1.75 2.1 57 SHEHLL C£HCLUoIZT3 Both static and dynncic tests have ostwbliahnd thnt thorn is a significant increase in the effective stiffness of a cushion when it is enclosed. This increase must be considered when designing yrotectivo packages. The energy absorb‘d by a cushion increases when tho lateral expansion of the cushion is restrained. Under static lending conditions, such as warehouse stocking, a cushion Would be able to ca; ort a grenter load than nornpl desig. figures would indicoto, but would also tronsmit a greater lond to the cushioned article, possibly csusing dn age. Use of conventional cushion-fnctor curves for cushion design may give insufficient protection. This will be p??- ticulnrly true when a cushion is tightly fitted into the container. This probably goes unnoticed in many cfisea bocnuss a “safety factor“ is added to the design thickness. This is a trial-snd-srror techni;uc, and is certainly not to be room mended as a general practice. The flexibility of the walls of tho container 2nd the free- dom of the cushion within the container may govern the degree of yrotection in some instvncos. ‘ RiliingfaiTlgho On the basis of the information gntnered in this study, several reconsendstions can be made for cushion design factor dcterninetion tests. Roth static and dynssic design-factor tests for pocksging use should be node with enclosed cushions in order to obtain results which more closely a groximnte actual conditions. Pnekcgos for cushioned articles should be designed lo-sely to gerwit some expansion of the cushion under stresses. If the nnture of the yroduct is not grohibitivs, cushioned pccknyes should be vented to redice the amount of sir trapped in the cushion when a stress is s3 lied. If pockrges csnnot be vented, then the iopnct ores of the cushioned article should be less than the cushion eras, to psrnit Air transfer within the packers. This lest will require a conyrosise design between usxinizing the article area to r duce stress and allow- int cirdmovement space. The use of cuskion factors as design elements should be reconsidered. The factors as currently determined are reaote fron what they should be and re-deter.inction with enclosures will not produce a curve having a mininwn, except jossibly at relatively high stresses. bUGGfieTIOYfi F93 FUVTflid “TUDIQS Tc gain a more thorough understanding of the energy absorption grorerties of enclosed cushions, the following any nations are offered. These ideas. have not been investigated sufficiently to estAblish their merit, and are offered with- Ont any recon endntions as to seouence or validity. The effects of friction between the cushion and container wells might be studied by methods similar to those of this study, using enclosure materials of varying smoothness and cushions of several surface densities. Measurement of horizontal forces due to cushion conpression would help in deteraining the reouired strength of the outer continer. The profortion of absorption increase due to lateral deflection might be studied by use of an open-sided enclosure that -ernits air to escape while restraining the cushion. Sone efforts in this direction were made during the current rroject, but the Vented enclosure ecnetructed was unsuccess- fill. Studies should be made to determine the relationship between nornel cushion footers and cushion behavior under actual conditions, with the intention of finding a new factor to reflwce the cushion factor. Such a factor should be determinate under various test conditions and n3;licnble to a wide range of applications. 60 (1) (53) (5) (4) LI )T OF RTFTZRC??? L3 Kaitb W. Kellicutt, A?”‘11¢9ti*& 9}; the iLrn‘iertiee 93: Cnshianing materials £Q_the Dnsggg‘gg'ouahiona, Report Ho. 1627, Forest Iroducta Laboratory, Eadiaon, Wisconain, raisquad 19C5. 3.3. Jones and W. L. Jaaea, Simnli?tnd Hethed of Snlpcting nhd Designig; kickers Cratinninn Lnt>rinls, deport NO. 2051, Forest kroducta Laboratory, Madison, Wisconsin, lfi55o R. R. Janaaen, Sfilecting_Pncka‘e Cufifiionint ”atfirinla to Provide Wintmum Containar_0ubngp, Nrrtn Aaerlcnn Aviation Corporation, Lug Angeles, California, bctober, 1932. H. H. Hates, “A Dynamic Cushion Tester-~1ta apylication to Cushion Design", Jaint Industry Conference on Cushioning in tacking, finyne University, December 1955. :6 . 3. Jones and W. L. Jaass, "Calculnting Cushion Requisitea', Modern‘ Packaging, February, 1956. 51 AL.=IQDIX I 73:32:}! c.:.mL'L..'..'zI-::::: FCR STATIC ‘I‘SSTS Tho absorbed energy for statically-loaded cushions was confutod as follows: Column 1 Colunn 2 Column 5 Column h Column 5 Column 6 Colu:n 7 Coluon 3 The drflection in increaonto of 0.1 inch. The moon load at each deflection joint, Iron the rocordor chart. Strain is conputed by dividing the deflection by tho original thicknaoc. Stress is the moon load divided by tho cushion area. The strain increzzont AG is the strain change over each increnont, token frog the strain data in column 5. The moon rtroso per increnont is calculvtod by adding tho stresses at the beginning and end of each incrcnont and dividing the own by two. The energy increoont is represented by the area under the increment, and in tho groduot of the strain increment and the mean stress in the increment. TMa suncation of the energies is the sum of the energies in the increments to the point under consideration. The lost figure in this column is the total energy absorbed in the compression test. a1;gutlt II UJS CF STKTIC HKJRGY iBZCRETICN DATA FOR CJZfiICH DJJIGR Stress-energy or stress-strain nnd strain—energy can readily be used to determine the energy wlich will be absorbed by a cushion for a given stress. As on exvnple, considor the care of an object with a flat surface area of 120 ejupre inches and a weight of 5.0 poundl. It is desired to yrotoct the object against shocks u: to 60 G's. Fron the formula F ZLflG/n, the streso is found to to 2,5 pound. for 3 acre inch. Using graph 15, for free grade IV cushions, the strain corresownding to a stress of 2.5 y,a,i. is 0.68 in/in. The energy aboorbod at this strain is 0.64 incharounds per cubic inch. This in the energy the cushion will absorb in protecting the packaged object at the maximum shock of 60 G'l. For an identical cushion enclosed in the fflCkflfie, the strain corresgonding to a stress of 2. 3.3.1. is 0.64 in/in (grnyh 14), and tom energy which is absorbed in 3.66 inch- pounda per cubic inch. Thin indicates that the enclosed cuehion obyorbte 5% more energy or that it transaite that much more energy to the ar+icle it is 6Xpect9d to yrotact. {3 smlss (poi) 1.: ‘ 1.0 0.8 O o O my (tum/1.3) 0A 0.2 7 I ‘ | | 1.1; Stress-Strain "'" "‘ Strain-Energy 6 F'- 1.2 5 — 1.0 S? A — 5 ”J; h 0.8\ a 3 v H I {73 .5 E Z w 3 "" 0.6 E»? B {a 2 —— 00h 1 .,.. 0.2 o .r” | | | o 0.2 0.1; 0.6 0.8 STRAIN (in/in) STRESS-STRAIN AND STRAIN-ENERGY CURVES GRADE IV ENCLOSED CUSHIONLS, NOT PIES'I'RESSED GRAPH 1h 65 A Eexslx III C’JWITN DJQIGR VIPH CJSnIQR FACTCR CURVJJ The use of cushion factors for design of cushions is a valuable technijue, since c shion factor-stress curves say be made up for the Various materials and filed for handy reference. To illustrate the use of cushion fsctors, consider the following hypothetical situnticns An object weighing 9.0 rounds and having an insect area of 500 sounrc inches is to be rrotwcted fr=r stocks ova 20 0'3 at drop heijkts up to 40 inches. Determinstion of the thickness of Type III cushions, rising the usual free cushion design curve, is sccqnplishvd sssily. The stress 13 :zs/A : 9 x 20/22 = 0.8:: 17.5.1. The cushion factor corresfonding to this stress is 1.87 (Grafh 9). The necessary cushion thickness '1‘ is than T = GEE/G :3 1.87 x 14'3/590 -‘-' 5.74 inches. However, for an enclosed cushion, Greek 9 also gives a cushion factor of 5.15 es the cushion factor for 9 stress of 0.39 9.5.1. This requires a t'f'lickness of T ='- CII/G =5.l§ 1: 43/?0 2:6.36 incres. his indicstes that about €Tfi more cushioning is nerded than nirht be indicated by the usual method. 66 A {3331i IV CKLIZT‘TICN 0? BY?‘ 18 ZTCCKJ'fiiiUHIHG AFPigiTUS 3 ‘L’IQ’I‘IEPIT 1‘33 EXIIFIC QTIC‘IISI Accelerosotor outrut - 8.6*mv/C r.m.s. Accelerometpr output - 3.6 x l.h14~=112.16 mv/G ycnk¢to-pcnk Cathode follower smnlificstion factor -- 0394 Noise Filter amplificstion factor .. 0.70 Input to oscilloscope -¢ 12.16 x 0.9 x 0.70'z 3.00 mv/G Isnk-to-fcsk Input to oscilloscope: 5.67 mv G r.m.s. CALliiiTION: Calibration was sccnnnlishod by feeding a signal equivalent to is 6'3 (54.6 mv r.n.s.) into the oscilloscope. The y-axis scale was adjusted to make the 13 G sirnsl fit five scale divisions (1“), so that the onlibrotion was 1/5'11 26's. This cslibrntion was used for a majority of the drop tests, but some tests had to be made using scales of 1/5" :34 or fifi's to got the full signal on tho screen. 67 “ ",t ‘ 7;-‘)‘\‘r' ‘-- 2.1m. I“ '\‘_v.‘.‘fi."I." *“= “ m I ““-"."‘“."-v saw-vol 1w iR'..LU4? I . .‘..);-LH’I.~IJ.J ‘ i)’.:. .J .04.“; .~~-...“'. ’A’hlni {Ji‘i ch dy1nydc tester ussd in this study is destined for the addition of a circuit to determine the velocity of the platen near the point of impact. The addition consists of an electronic switch which controls tbs counting t'os of the decade counter. The photocell box Will b3 nodified to use two calls. when the filoton falls, an srn will sctustc he two photocolls in secucncs. Tho decode counter will receive a sine wave signal, and the number of cycles clnpsing during the time when tho flotcn ans trijs the first and second gwotocslls will detersino the claysod time. This tiao and tho distance bs‘ucen the two photocell slits can be used to dstoruiuc the rlntcn velocit‘. The switch must also actuate the sweep trig;sr of the cscillosco;s, and a contact is provided for this purgosc. 68 01"..“ '7' A».I£DIx VI ADDITIfHQL 33LICTIJ R~A311I63 CW USIIC‘EIITIG 5.35,) ...1_’>CK «boOh‘i ICE! 0. 3. Grade Vibration and fihock Isolction, John Wiley and Sons, flew York, 1931. J. L. Gretz "E; wine ring a Cus‘r ioncd rackcje , Lioficrn Foo¥7“ifi?, Roy iOrfi, ml . ficf Package Jones, “Denonotretion of Basic Princ " ' oniflg in . i Czshionicg , Joint Industrv Confcrenco on Co std Packing, Hcyno Univorsitv, Docoflbor, 1953. -. Hoool, 5 ”ntbomaticnl Approach to Cushioning",‘fodarn fnck‘r'iar' 175.1,. W' .. ' t R. D. "indlln, 'D"no ica of Iflck“ro Cushioninig, Eéll _ 3.an, T fi"hicf\1T’)H‘m01_’ ,. {onmrrra \.h B 1716/, (10:03:33, 1945. A. K. Undcrhill, “What Makes Cushioning work", Undrrn Enteriwle ””WAIiWZJ Eochbor, lfifii 7O 91r2ula+icn depto “A" 2' 1961 up x NOV 3 a 1969 .2391" .D’o W J HICHIGRN STQTE UNIV. 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