AD-A008 020

LAMINATES FOR BALLISTIC PROTECTION

Roy C. Laible, et alArmy Natick LaboratoriesNatick, Massachusetts

February 1,975

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LAMIRATI FcU SUMMIWC 1!PRNSfON Technical Report

S.PKRIVORMINWOnRg. REORT NUMBER

7- 6. CONTRACT OR GRANT 10511111("4

Roy C. Laible and. 1burice Re Denommee

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138 rmy ti@I labret~ioi62723', 1T762723A398)lhtiok,, M& 01760

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17, DIST RISUTION ST ATEMEN T (at the abstract antoed. In Block 30, it different From Reprt

1S. SUPPLERMENTARY NOTES

19. KEY WORDS (Contlnuw an reverse ai.e IfnecelovarE dridontily41 bl Sock nimaher)4

Laminates,, Ballistic Protection, Keviarq Fiberglass., Armor,Mechanical Properties, Ibenolicl, Polyester, Pre-preg, Laminating

30. ABSTRACT (Continua an revoem oldo It neceossar and IdEtitDh' bY block RUMuier)

Kevlar 29 and. fiberglass laminates were ballistically evaluated with9 Improjectiles to deteraine their ability to protect against severehand gun threats.The Kevlar laminates exhibit an advantage over the glass laminates,,providing complete protection against 9 mm projectiles up to 395 m/secat an asreal density of 7.3 Wi/gs The glass laminates allowed som

c let e netratious even at a hiaher areal denuityDD JS143 EITO P O55I bSLTDD J N 7 173 OIIO OFI OV 5 s OSOK I UWIA5IFID

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ABSTRACT (coat'd)

The mechanical properties of the Kevlar and glass laminates have beencompared in an attempt to determine the mechanism by which they stop orslow down missiles. The Kevlar laminates do exhibit considerably higherstatic tensile strengths along with slightly higher eloWgtions to breakthan do the glass laminates. This ability of the Kevlar to absorb moreenergy may be one of the Important factors in providing the improvedballistic protection.

The comparative resistance of the glass and Kevlar laminates to cyclicbending was compared to determine mechanical weaknesses of the laminateswhich might lead to failure through ale and handling prior to exPosure toany ballistic Impact. The Kevlar laminates do plastically defom butsurfive many more high load cyclic deformations than do the glas" laminsteswhich tend to catastrophically fail under similar conditions of test.

IJ

/I UIFIA WIO30DSECURITY CtLASSiFiiCATIUN OPe THIS PAOE[lP~men DOI ata *te,.d

p!

19 Fabiocu 2

a. KoCsla.r 29 Fabrio 2

be .lass-o.v.-Ro..O. 2

2. Pro-prog

C. Ballistic Tesitng3

D, D •c•ulo Tooting3

iinMWi AMD ZOUISON

A. •onis.tic Puefoumaoo

3. Mechanical Properties iCONWSIOI 7

ACKIMZMGUS 8...l ..E. .. 9

,t

i:i•: . _ 3

TAKI I co marluon of BILlistIc PerormUc0 of GlassanI GUvlar 1 S a mi nates (10 7 aiat ) Agfstie

the 9 vM Proeecttle

ITGU 12 CokSurison of Ballistic Performance of Glass .a,,d Uvl,,r.29 Lamiates (8.2 kg/m) Against,the 9 vm t Projle Proe

TAUX 117 Comparison of the Bonding Moment Proporties of

IaGR3 o es eof M lass land aevlar 29

TAN I'V Tensile StrAngtz lDaa on Variko e Kevlar and 6Glass Lamiates

PIT= 1 Tack Surface of Glass Laminate After 1M3.tiyle 10l•ats with 9m Projectile

FIGME 2 Back Surface of Kevlar Laminate After Multiple 1OImpacts with 9m Projectile

FIGMM 3 Top Surface of Kevlar Laminate After 10030 11C~vles at A Maxima Load of 90 ka• (bandingmode)

FTOM 4 Top Surface of Glass Laiatea~ After 3.1cyceso 32at A Maxium Load of 61 kg (beading mode)

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4!

•' ............ "r..... . . .. n . .. . .. • I V'III ' -

INR0DCT~ION

teMost of the publidshed work on composites of glass and Keviar hastestated application of pro-dding structural components for airplan%

k boats and other consumer goods. Theme composites generally possessrelatively low fiber fractions (60$ weight Percentage) aul. utilize

resrs ndcoupling agents designed to provide good adhesiomi and. stress

On the other handi, the glass laminates usually used for ballisticProtactive applications utilize woven roving fabric treated. withstarch - oil size and a high volume fraction of fiber (75% by weight).Theme factors decrease the adhesion an& tend to 4;ve lower she,,rresistance and. poorer stress transfer. In fact,. delamination underthe stress of ballistic Impact, my be an advantage leading toIncreased energy absorption* The develapmnut of Keviar 29, an aromaticpolysmide fiber., has., for the first time., Introduced a wholly orguzai.fibrous reinforcement with a modulus and heat resistance comphitivewith glass and a tensile strength superior to glass * The Propertiesof tho Keviar 29 itself have been outlined previously (2,3) I

The present paper describes work conducted to prepWar laminatesof glass and IKsvlar .29 and to determine their ability to provideprotection against a severe hand gu threat, the 9 mm 'pistol ballt.In addition, the mechanical properties of the glass wan Kiavlarcomposites prepared for the above use ire compared in an attemt todetermine reasons for their ability to stop and mlow down missilesas well as weaknesses which might lead to mecaniclal failure priorto missile Impact,

A. Materials

1. Pabries

a. Kevlar 29 Fabric

Te Kevlar fabrics used were a 0o.17 kg/ 2 (5 o0/7d)8 Ramwos Satin ppaed from 44 taex (400 denier) yam in a28 x 28 couna t and a O.J4 kg/M (13 oz/yd2 ) 2 x 2 basket weaveprepared from 167 tex (i100 denier) Yarn in a 35 x 35 count.

b. Glass-Woven-Roving

The gUlaso-woven-roving was a 0,78 kg/u 2 (23 oz/yd,2 )starch oil sized fabric (J. P. Stevens #1357) prepared from 3

2.

a. The Kevlar 29 fabric was Ilpregnated with an acidcure thermosetting resin system consisting of the followingmajor components:

(1) Polyvinyl butyral (iD)

(2) ftlathylol phenol

(3) Pheol formaldehyde

fte 0.17 kg/r 2 fabric was coated to obtain 30-3ie.% resin pickup(final weight) while the heavier weight Kevlar fabric 0.44 k/um2was coated to 20-24% pickup. Solids of

Components Parts b. Weigt Total Solids

WE 18-20% hydroxyl 868.0 47.2(25% solid in ItCH)

Phenol formaldehyde 100.0 12.1(e7h solids)

Trimethylol phenol 267.0 34.8

(60% solids)

Phthalie anhydride 85.6 5.6

Methanol 51.2 -

2

. .........-

b. The glass fabric was impregnated with an unsaturated.polyester resin modified with diallyl phthalate using a hightemperature catalyst system. The fabric was coated to obtain 23-25$resin pickup (final weight).

B. ftenaration of laminates

nlat liminates of Xevlar were molded byr placing the appropriatenumber of plies of pre-preg to obtain the desired areal densitybetween two sheets of a glass scrim Teflon coated release agent.

or two minutes the pressure was released to permit the structure to[e& n hnwsrapid h ieo degassing varied with theamount of volatiles In the pre-preg which Isrelated to the pre-pregage and treatment. Insufficient degassing can be detected byblistering of the final laminate. Laminates were removed hot fromthe Wress and allowed to cool to room temperature.

Flat laminates of glass were molded in a similar manner but atK a much lower pressure of 0.85 MPa, (125 psi) and a temperature of13800# Cycle Interruption was not necessary in the case of theglass laminates because volatiles are not produced.

C. Ballistic Testing

All ballistic testing was conducted at the Biophysics Laboratory,,Edgewood Arsenal, MD, using 8.0 g (12J4 grain) full metal jacket 9 mprojectile. The projectiles were tired from a 9 =Ma Inn barrel iastnhand loaded cartridges. Velocities from 335-396 u/sec (1100-1300 ft/sea)were obtained.

Do nnrical Testing

1. Bending modulus was measured in accordance with Method I ofATM D790-71, "Flexural Properties of Plastics."

2. Tensile properties were measured in accordance with ABTMD638-72) 'Tensile Properties of Plastics."

3. Interlaminar shear was measured in accordance with AMID2733-70o "Interlaaiinar Shear Strength of Structural ReinforcedPlastics at Elevated. Temperaturea." Testiaig was conducted at23 t 200 and 50 t2% relative humidity.

3

RPBUT8 AND DISCUBION

A. Ballistic Performance

The Kevlar 29 and glass-woven-roving laminates were subjectedto ballistic impact with the 9 mm projectile. At the heavier arealdensity of 10.7 kg/m2 (35 oz/fb2) the Kevlar laminates had nocomplete penetrations even at an impact velocity up to 375 m/sec(1230 ft/•s•/ea). e glass-woven-roving at this same areal densityhad defeated the projectile four times and had one ccmp3etepenetration (Table I).

TADIA I

Comparison of Ballistic Performance of Glass and Kevlar 29Laminates (10.7 kg/m2 ) Against the 9 mm Projectile

Ynberof Velocity Range

Material y (m/se6) Results

Kevlar 29 10 357-375(1172-1230 ft/sec) 10 - No Penetrations

Glass WR 5 352-359 4 - No Penetrations(n155-n178 ft/sec) 1 - Penetration

(359 2/see)

The laminates vere also fired at a reduced areal density8.2 kgl/ (27 oz/ft'l). A total of nine impacts on the Kevlarlaminate produced nw complete penetrations. In the case of theglass-woven-roving laminate, four out of five impacts resulted incomplete penetrations. Those results showed that at least for thisthreat, Kev7r possesses an advantage over glass.

TAILI II

Comparison of Ballistic Performance of Glass and Kevlar 29Laminates (8.2 kj/1W) Against the 9 =u Projectile

NberMaterial of Velocity Range

5 (2/see) Results

Kevlar 29 9 358-364 9 - No Penetrations(n1761196 ft/see)

Glass WR 5 352-367 1 - No Penetrations(1155-1204 ft/see) (352 u/see)

4 - Penetrations

4.-

IAn additional advantage of the Kevlar laminates can be seen inFigures I and 2 which show the back surfaces of the laminatesafter ballistic impact. The glass laminate shows considerablymore back surface deformation and delaminatio, than does theKeylar.

T.•e Kelar laminate was prepared from a lightweight (0.17"ikg/am) relatively high cost fabric. The ballistic experimentswere repeated using the heavier weight Kevlar fabric (0.14 kg/m2 )prepared from less expensive 167 tex yarn. Even a lover totalweight of this material (7.3 kg1mF) laminate)) was able to stopall 9 m projectiles fired at even higher velocities up to395 usc

B. Mechanical Pro~erties

The relative low cost of the glass-woven-roving ($2/kg)compared to Ievlar 29 ($15/kg) makes it imperative that glassand Kevlar 29 be compared structurlly before any decision Is A,,made on the use of either in applications such as helmets forpolice or military use. The first test selected was that of thebending moment. Utilizing a 100 m span length on 2e. 4mmwide strips tested at 2.54 mn/mao, the following redu.Lts wereobtained (Table III):

TAMA3 III

Comparison of the Bending Moment Properties ofLaminates of Glass and Kevlar 29

Areal Max Fiber BendingMaterial Desi tream Modulus Mix Load.

Glass 6.1 165.14 19.3 293

Kevlar 29 6.1 95.8 7.58 377

Glass 11.6 185.3 20.7 387 -I

Kevlar 11.6 110.2 9.6 1289

For both bending modulus and maximu fiber stress, the glassappears to be favored. However, the actual loae at yield ishigher for the Kevlar 29 than for the glass. This is especiallytrue for the Keylar at the heavier areal density (11.6 Qk/m 2 ).The areal densities were selected to bracket those used for theballistic tests.

5

FI

It was noted in the bending tests Just described that whilethe Kevlar yields without visible failure,, the glass shows theinitial signs of fracture. For this reason it was decided toinvestigate the effects of repeated cycling upon the resultantproperties of the two competitive materials. Repeated bendingtests were conducted on thl Kevlar and glass laminates using anareal density of 11.6 kg/m and a maximn load of 82N (200 lb.).The Kevlar lamintes survived 1000 cycles but exhibited someplastic defomation while the glass laminates after only 100cycles were delaminated and fractured to a degree that they retainedessentially zero bending modulus and low tensile strength. Picturesof typical speclmens ere given in Figures 3 and 4.

Both composites with their very low resin content would beexpected to exhibit relatively low Interlaminar shear valuescompared to those composites prepared for structural applications.The measurement of Interlaninar shear is another useful indicatorof the relative structural Integrity of the glass and Kevlarlaminates. Such tests war~ conducted on both laminates at anareal density of 11.6 kg/m utilizing a crosshead speed of 0.25urn/min and typical 25.4• u wide specimens with a 12.7 = distancebetween saw cuts. The Interlaminar shear values averaged 10,1 Nea(1470 psi) for the glass laminates and 29.2 Xfa (4240 psi) for theKevlar laminates. These values suggest that the Kevlar laminatdsshould possess greater structural integrity during tough handlingthan would glass.

The last comparison conducted was that of tensile strength.Type 11 AMS• tensile specimens of Kevlar and glass laminates,

prepared in several areal densities, werembjected to tensiletests with the following results:

TABLE IV

Tensile Strength Data on Various ievlar and Glass Laminates

Number Areal Density Elongation- TensileMaterial of Plies (kg/m2) to-Break (•) Strength (MPa)

Kevlar 5 3.0 - 531Kevlar 10 6.1 - 420Kevlar 14 8.2 3.942Glass 6 8.2 3.0 289Kevlar 20 11.6 - 438Glass 9 11.6 - 262

6

Elongation-to-break values are given in Table TV only for thosetests in which an extensometer was used to measure elongationto failure. In these two cases the laminates are those usedfor the ballistic tests. Purthermore, the larger elongation-to-break (3.9%) exhibited by the Kevlar combined with the highertensile strength 427 lea (62,000 psi) results in higher work to

•Ii ,rupture values. These higher work to rupture values Way in turnbe responsible for the ballistic advantage of Kevlar iainnatesover that of glass laminates. Tensile tests conducted at astrain rate one decade faster raise the tensile values for theglass laminates 5 - 10% with a much smaller improvement shownby the Kevlar. This may aacount for the fact that the Slaslaminates are somewhat competitive with Kevlar ballisticallydespite the rather large difference in static tensile strengths.Although the mechanical properties (tensile strength, interlaminarshear and behavior under repeated bending) all sm to favor theKevlar laminates, actual field tests of the proposed items(helmets, vest inserts) would be required to determine the actualability of the materials to maintain their integrity under serviceconditions.

CONLUSIONS

1, Both glass and Kevlar laminates possess a potential forproviding protection against small arms fire.

2. Using the highly penetrating 9 mm projectile at velocitiesas high as 375 m/sec (1230 ft/sec), the Kevlar laainatespossess an advantage over glass with no projectilespenetrating the laminate even at the lowest areal densitytested (7.5 kg/mrn). Even the less costly, heavier denierKevlar yarn produces a suitable fabric for the laminate.

3. Backside damage and delamination from ballistic impact isless for the Kevlar laminates than for the glass.

4. The results of the tensile tests show that Kevlar 29 laminateswould be expected to sustain higher energy Impacts than glasslaminates because of the higher tensile strengths andelongations-to-break exhibited by the former material.

5. The other mechanical tests conducted (interlaminar shear,bending, cyclic bending) appear to favor Kevlar. Actualuser tests will be necessary to determine the advantm.eof Kevlar in resistance to mechanical abuse.

7

The authors vould like to acknowledge the support of Mr. osterShubin of the Isv Mnforeament Assltance Administration and Hr. lekNb4taamrelll an Mr. MEwad Hawkins of dewvood Arsenal. Dr. R•obertProsser a n r. eoreorp Tomssian of Natick IAboratories wereresponsible for the photo•raps shown.

8

Sen.I * .JL•J.e1-~

1. Moore, J. W., Miner, L. Hl., Riewald,, P. 0. and Wale, D. C.,"Recent Advances in PAD-49 Compositesp" Paper presented at4th National SAM Technioal Conference, Palo Alto, CA,Cotober 17-19, 1972.

2. Laible, R, C., Figucia, P. and. Kirkvood, B.e, "Scanning ZlectronMicroscopy an Related to the Study of High-Speed. Fiber Duipact,,J. Applied Polymer Science" Applied Polymer Syposium #23,pp 181-191, May 1974.

3. Hansen, J. V. E. and Laible, B. C., "Flexible Body ArmorMaterials," Paper presented at National Symposium of FiberFrontiers, June 10-12, 19714, Washington, DC.

9

III)

FIG, 1 Back Siarfaoes of Glass Laminate AfterMultiple mIpacts with 9 mProjectile

A MI. 2 Back Surface of Keviar Li1nat. AfterMaltiple Impacts with 9 vmt Projectile

10

'tO

IG. 3 Top Surface of Keviar Laminate After1000 Cycles at A ?&Iwwl~ Load or 90 kg

FIa. 4 Top Surface of Glass Laminate After11 Cycles at A Maximum load of 61 kg