NUMERICAL SIMULATION OF IMPACT ON CERAMIC ARMOUR SYSTEM.docx
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NUMERICAL SIMULATION OF IMPACT ON CERAMIC ARMOUR SYSTEM.docx
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NUMERICALSIMULATIONOFIMPACTONCERAMICARMOURSYSTEM
NUMERICALSIMULATIONOFIMPACTONCERAMICARMOURSYSTEM
Theworkreportsonnumericalsimulationofimpactproblemsonceramic/aramidarmoursystemsbackedwithKevlar29.TestswereperformedwithSTANAG2920fragmentsandNATO5.56bulletsdrivenatvelocitiesupto1100m/s.Inordertoobtainthebestballisticefficiencyofthecompositearmoursystemthreeconfigurationsofthearmoursystemwastakenintoaccountinnumericalsimulations,varyingthethicknessofceramicfrontplate.Thethicknessofbackedplatewasmaintainedconstantat2mm.Theconfigurationsarecontemplatedinthetable1.
Table1
Configuration
Ceramic/Kevlarthicknessratio(h1/h2)
C1
5
C2
7.5
C3
9.5
Theballisticperformanceofthelightweightarmoursystemswasexaminedtoobtainanestimatefortheglobaldamageofthecompositeplates.
Materialmodels
TheMohr-Coulomb(MC)strengthmodelandlinearequationofstate(EOS)areusedtomodeltheceramiclayer.Themicromechanicalfailureofceramicismodelledusingacumulativedamagemodel.Sinceexperimentsindicatethatceramicsshowamarkedincreaseincompressivestrengthasthehydrostaticpressureisincreased,itismostlikelythatthismodelwillbeusedinconjunctionwiththeMohr-Coulombmodelwhichusesayieldstrengththatisafunctionofthelocalhydrostaticpressure.
Anadvancedorthotropicmodel[1]implementedinAutodynhydrocode,whichusenon-linearequationofstateinconjunctionwithanorthotropicstiffnessmatrixisusedtomodeltheKevlar29/Epoxylayer.
The4340steelusedforSTANAGfragmentswasrepresentedusingtheJohnsonCookstrengthmodel,whichincludestrainandstrainratehardeningandthermalsofteningeffects.
AmodeloftheNATO5.56bulletwasdevelopedusingmaterialdataavailablefromexistingAutodynmodellibrariesandparametersmodifiedbaseduponthemeasuredhardnessofthebullet´sindividualcomponents.Thebulletisofthree-partconstructionwithahardsteeltiparelativelysoftleadcoreandacooper-alloygildingjacket.Thereisasmallgapbetweenthefrontofthesteeltipandthegildingjacket.Thenominalmassofthebulletis4.0gandithasanaveragevelocityof1100m/swhenfiredfromastandardproofmountandwithastandardcartridgecase.
AshockequationofstateandJohnson-Cookconstitutivemodelwasusedtosimulatethematerialresponsetodynamicloadingofbullet´stipwithyieldstressYS=1539MPa.ThecoppergildingmetalwasmodelledusingsimplelinearequationofstateandJohnson-Cookconstitutivemodel,thetieldstressYS=330.75MPa.TheleadcorewasmodelledusingasimplelinearequationofstateandaSteinberg-Guinanconstitutivemodel,theyieldstresswassetatYS=20MPa.Thefailureofjacketwassimulatedusingaprinciplestrainfailuremodelsetat90%.
Thematerialmodelsanddataaresummedupinthefollowingtable.
Table2Materialdata
Ceramic-Gceramic(Autodynmateriallibraries)
StrengthModel:
Mohr-Coulomb
Pressure#1(kPa)–5.00E5
Pressure#2(kPa)0.00
Pressure#3(kPa)1.01E20
Pressure#4(kPa)1.01E20
YieldStress#1(kPa)0.00
YieldStress#2(kPa)3.80E6
YieldStress#3(kPa)3.80E6
YieldStress#4(kPa)3.80E6
Failure:
CumulativeDamage
Eff.Pl.StrainatZeroDamage:
0.01
Eff.Pl.StrainatMax.Damage:
0.03
MaximumDamage:
0.7
Equationofstates :
Linear
Referencedensity(g/cm3) 3.43
Bulkmodulus(kPa)1.54E8
Strength :
Mohr-Coulomb
Shearmodulus(kPa)8.30E7
Failure :
CumulativeDamage
ReferenceTemperature(K)300
KEVLAR/EPOXY-EMI
TensilefailureStress11(kPa) 5.00E+04
MaximumShearStress12(kpa) 1.00E+05
TensileFailureStrain11 0.01
TensileFailureStrain22 0.20
TensileFailureStrain33 0.20
PostFailureResponse Orthotropic
Fail11&11Only
Fail22&22Only
Fail33&33Only
Fail12&12and11Only
Fail23&23and11Only
Fail31&31and11Only
ResidualshearStiff.Frac.0.20
Equationofstates :
Orthotropic
Sub-EquationofStates :
Polynomial
Referencedensity(g/cm3) 1.40
Youngmodulus11(kPa) 2.392E+05
Youngmodulus22(kPa) 6.311E+06
Youngmodulus33(kPa) 6.311E+06
Poisonsratio12 0.115
Poisonsratio23 0.216
Poisonsratio31 3.034
Strength :
Elastic
Shearmodulus(kPa)1.54E+06
Failure :
MaterialStress/Strain
4340Steel
EquationofStates :
Linear
Referencedensity(g/cm3)7.83
Bulkmodulus(kPa)1.59E+07
Referencetemperature(K)300
Specificheatcapacity(J/kgK)477
Strength :
Johnson-Cook
Shearmodulus(kPa)8.18E+07
YieldStress(kPa)7.92E+05
Hardeningconstant(kPa)5.10E+05
Hardeningexponent0.34
Strainrateconstant0.014
Thermalsofetningexponent1.03
Meltingtemperature(K)1793
Failuremodel :
None
Numericalmodels
Asthehighvelocityimpactphenomenonisoflocalisednature,theboundaryconditionsd
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