DTIC ADA543984: Bio-inspired Armor Protective Material Systems for Ballistic Shock Mitigation

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MaterialsandDesignxxx(2011)xxx–xxx
ContentslistsavailableatScienceDirect
Materials and Design
journal homepage: www.elsevier.com/locate/matdes
Bio-inspired armor protective material systems for ballistic shock mitigation
Jinhua Huanga,⇑, Helen Durdena, Mostafiz Chowdhuryb
aM4Engineering,Inc.,4020LongBeachBlvd.,LongBeach,CA90807,USA
bArmyResearchLaboratoryLiaison,2511JeffersonDavisHwy.,Arlington,VA22202,USA
a r t i c l e i n f o a b s t r a c t
Articlehistory: Severetransientballisticshocksfromprojectileimpacts,mineblasts,oroverheadartilleryattackscan
Received29January2011 incapacitateanoccupantatlowfrequencies,orsensitiveequipmentathighfrequencies,iftheyarenot
Accepted25March2011 properlyattenuatedbyarmorprotectivesystems.Uniquechallengesexistindevelopingarmorprotective
Availableonlinexxxx
systems formitigating both low and high frequency ballistic shocks due to the lack of robust design
methodology,theseveredynamicloadingconditions,andtheuncertaintiesinpredictingballisticshock
Keywords: responses.
B.Foams
Natureoffersengineersablueprintofhighlyeffective,efficient,andadaptivematerialdesignstopro-
E.Impactandballistic
tectcertainregionsfromexternalthreats.Thispaperpresentsthemodeling,analysis,design,optimiza-
G.Coupontesting
tion, fabrication, and experimental validation of bone-inspired armor protective material systems for
reducingprojectilepenetrationsandalleviatingballisticshocksatbothlowandhighfrequencies.The
optimizedbone-inspiredarmorprotectivematerialsystemhasasoft–stiff–soft–stiffmaterialdistribu-
tion pattern based on bone-foramen and osteonal-bone material systems. Analysis and experimental
resultsdemonstratedthatthebone-inspiredarmorprotectivematerialsystemshaveexcellentcapabili-
tiesfordrasticballisticshockmitigation,weightsavings,andsignificantreductionsinpenetrationand
loadtransmissionunderballisticloadingconditions.
(cid:2)2011ElsevierLtd.Allrightsreserved.
1.Introduction Thisisduetotheseveredynamicloadingconditions,theuncertain-
tiesinpredictingballisticshockresponses,thedifficultyinselect-
Thenecessityofconsideringballisticshockeffectsinnewvehi- ing proper constituent materials, and difficulties in determining
cledesignshas beenwellrecognizedin thecombatvehiclecom- criticalmaterialandgeometrydesignvariables.
munity during the past two decades [1]. A ballistic shock results In ballistic shock analysis, finite element based commercial
fromasignificantamountofconcentratedenergydepositedfrom software, especially LS-Dyna, has been predominately utilized to
caliberprojectileimpacts,mineblasts,oroverheadartilleryattacks calculatethetargetshockresponsesincludingaccelerationhisto-
ontoasmallareaofamilitaryvehicle[2].Thisenergymaybetrans- ries, shock response spectra, deformation, penetration, velocities,
mittedthroughoutthevehicleincludingareasfarawayfromand andseverityindices[4–6].Duetothehighfrequencyrangeofbal-
not exposed to the incident agent. At low frequencies (up to listicshock,thefiniteelementbasedmethodscanbecomeintrac-
1kHz), the ballistic shock response is dominated by high load table for large structures. A statistical energy analysis (SEA)
transmissionsandlarge-magnitudeflexuralvibrations,whichcan method was investigated for the prediction of ballistic shock in
be fatal to humansin a demanding high-g environment. A shock combatvehicles[1].Comparedtoconventionalanalysismethods,
of100gfor3msor40gfor50mswillcausesevereinjury[3].At theSEAmethodresultsinfastermodelconstruction,smallermod-
highfrequencies(above1kHz),theballisticshockresponseisdom- elsizes,shorterrunningtime,andareducedsetofinputparame-
inatedbythepropagationofthestresswavesinthevehiclemate- ters. However, the SEA predictions at some locations within the
rials, which will damage the light, intricate, frequency-sensitive testcomponentmightdisagreesignificantlyfromtheexperimental
componentssuchaselectronicsandoptics.Despitetherecognized measurements[1].
increasing demand for innovative lightweight armor protective Manyeffortshavebeenmadetomitigateballisticshocks.Trabia
systemscapableofmitigatingbothlowandhighfrequencyballistic etal.,employedsideandbottomL-shapepaneljointsforacombat
shocks, the development of the enabling techniques to support vehicletomitigateballisticshocksfromprojectileandblastattacks
sucharmorprotectivesystemanalysisanddesignhasbeenslow. [5,6]. The optimization results showed that the average of the
meanofaccelerationsatcriticallocationsincommanderanddriver
seats and instrumentation panels could be reduced considerably
⇑ Correspondingauthor.Tel.:[phone];fax:[phone]. by extending the joint and reducing its thickness. One drawback
E-mailaddress:[email protected](J.Huang). of the panel joint approach is its strong dependence on applied
0261-3069/$-seefrontmatter(cid:2)2011ElsevierLtd.Allrightsreserved.
doi:10.1016/j.matdes.2011.03.061
Pleasecitethisarticleinpressas:HuangJetal.Bio-inspiredarmorprotectivematerialsystemsforballisticshockmitigation.JMaterDesign(2011),
doi:10.1016/j.matdes.2011.03.061
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Bio-inspired armor protective material systems for ballistic shock
5b. GRANT NUMBER
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13. SUPPLEMENTARY NOTES
14. ABSTRACT
Severe transient ballistic shocks from projectile impacts, mine blasts, or overhead artillery attacks can
incapacitate an occupant at low frequencies, or sensitive equipment at high frequencies, if they are not
properly attenuated by armor protective systems. Unique challenges exist in developing armor protective
systems for mitigating both low and high frequency ballistic shocks due to the lack of robust design
methodology, the severe dynamic loading conditions, and the uncertainties in predicting ballistic shock
responses. Nature offers engineers a blueprint of highly effective, efficient, and adaptive material designs to
protect certain regions from external threats. This paper presents the modeling, analysis, design,
optimization fabrication, and experimental validation of bone-inspired armor protective material systems
for reducing projectile penetrations and alleviating ballistic shocks at both low and high frequencies. The
optimized bone-inspired armor protective material system has a soft?stiff?soft?stiff material distribution
pattern based on bone-foramen and osteonal-bone material systems. Analysis and experimental results
demonstrated that the bone-inspired armor protective material systems have excellent capabilities for
drastic ballistic shock mitigation, weight savings, and significant reductions in penetration and load
transmission under ballistic loading conditions.
15. SUBJECT TERMS
16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF
ABSTRACT OF PAGES RESPONSIBLE PERSON
a. REPORT b. ABSTRACT c. THIS PAGE Same as 9
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Prescribed by ANSI Std Z39-18
2 J.Huangetal./MaterialsandDesignxxx(2011)xxx–xxx
load locations. Doney and Sen studied the shock mitigation effi- 2.Conceptformulationofbone-inspiredarmorprotective
ciencyofmetallictaperedchains(highlyscalablegranularmedia) materialsystems
[7].Whilethemetallictaperedchainarmordemonstratesnotice-
ableshockabsorption,itlacksgoodpenetration-resistancecapabil- 2.1.Naturalboneprotectionmaterialsystems
ity, its heavy weight scarifies the vehicle’s mobility, and its
fabrication is not cheap. Polymer–matrix composite (PMC) based Thebone-foramen(Fig.1)andosteonal-bone(Fig.2)protective
armorwasdevelopedtoimprovetheballisticperformanceofrap- systems of the equine third metacarpus (MC3) consist of foam
idly deployable lightweight vehicles [8]. However, revolutionary materials. The homogenized elastic modulus (E ) and strength
bone
improvementsinPMC-basedarmordesignsarerequiredtoreach (r ) of these foam materials increase with the bone apparent
bone
Armymyriadperformancegoalsforballistic,structural,shock,fire, density (q ) and can be expressed by the following power law
bone
cost, and signature. Dharmasena et al., investigated the dynamic functions[12–14]:
mechanical response of square honeycomb panels made from a
super-austeniticstainlesssteelalloy[9].Thebenefitsofthesquare Ebone¼aqbbone ð1Þ
honeycombpanelsforblastmitigationareparticularlyevidentat
low impulsive levels, but at high impulse levels, the benefits r ¼aqb ð2Þ
bone bone
diminish.
Through millions of years of evolution to solve load-bearing wherea,a,b,andbareconstantsandb/b=0.5forosteonalbones.
problems and adapt to a given environment, nature offers Experimental measurements and property correlations for the
engineers a blueprint of highly effective, efficient, and adaptive bone-foramenandosteonal-bonematerialsystemsrevealedthefol-
material designs to protect certain regions from external threats lowingimportantfeatures[12,13,15]:
[10–12].Thebone-foramenmaterialsysteminaregionofahorse’s
third metacarpus (Fig. 1), which is located in the forelimb of the (cid:2) Thematerialdensityandpropertyarespatiallygraded.
horse, consists of a foramen (natural hole) and foam materials, (cid:2) Thereexiststiff,strongregionsandsoft,weakregions.
andissubjecttoimpactloading.Thenormalhorsethirdmetacar- (cid:2) Thereisnodiscontinuityindensityorpropertydistributionsat
pus is osteonal-bone that is composed of interstitial (lamellae), thejuncturebetweendifferentregions.
cementline,andosteons(Haversiansystems)(Fig.2).Bothbone- (cid:2) Materialpropertyvariations are limitedtoregionsaround the
foramenandosteonal-bonematerialsystemshavedevelopedvery foramenandwithinthecementlineandintra-osteon.
robustdesignpatternstoprotectbloodvesselsandnerves.Exper- (cid:2) Thereexistspecialfiberorientationdistributionpatternsincer-
imental measurements on bone-foramen and osteonal-bone tainregionsasopposedtonormalfiberorientations.
material systems have revealed stiffness distribution patterns (cid:2) Osteonal-bonehasaneffectivecrack-stoppingmechanism[15].
due to functionally graded density variations [12,13]. The bone-
foramen material system has a soft region near the foramen and 2.2.Parallelsbetweenboneandengineeringdesigns
astifferregionsomedistanceaway,comparedwithnormalbone
properties (far field). The modulus in the osteonal-bone material Inbothbone-foramenandosteonal-bonematerialsystems,the
system has a relatively high value in the interstitial matrix field designsareachievedthroughmechanicalpropertygradationunder
andgraduallybecomessmallerinthecementline.Itreachesahigh weightconstraintsandimpactloadingconditionsandthedesigns
valueagainintheintra-osteonregion. aimtoprotectinternalregionsfromexternalthreats.Inthevehicle
Greatparallelsexistbetweenthehorse’sthirdmetacarpusand armorprotectivesystemdesign,theweightisalsoconstraineddue
engineering armor protective systems in material constituents, tomobilityrequirementandthedesignalsoaimstoprotectinter-
loading conditions, design goals, design constraints, and design nal regions from external threats due to projectile impacts and
methodology[12].ThisledustoaUSArmysponsoredefforttode- mine blasts. The design spaces for both bone and vehicle armor
velopaninnovative,lightweightbone-inspiredfunctionallygraded protectivesystemsareverylimited.
armorprotectivematerialsystemforballisticshockmitigationand Similartotheutilizationoffoamsinbone-foramenandosteo-
penetrationreduction.Thecurrentpaperpresentstheresearchre- nal-bone protective system designs, metallic foams have found
sultsforthebone-inspiredarmorproject.Inwhatfollows,wefirst applications in vehicle armor designs [16,17]. For both bone and
describe the concept formulation of bone-inspired armor protec- metallic foams, the material properties (modulus, strength,
tivematerialsystems.Next,wepresenttheanalysisandoptimiza- Poisson’s ratio, etc.) depend on density. The bone-foramen and
tionofbone-inspiredarmorprotectivematerialsystems.Then,the osteonal-bone material systems optimize mechanical property
enhancement of the optimized bone-inspired armor protective gradationsbyspatiallyvaryingthebonefoammaterial’svoidand
material system is discussed. Experimental validation is given in solid phase distributions. Similarly, the spaced vehicle armor de-
Section5.Finally,wedrawconclusionsinSection6. sign utilizes the spatial void (spaces between plates) and solid
Second
Third Metacarpus Metacarpus a)
P
G
s (
u
ul
d
Proximal mo
Proximal Phalanx Sesamoids al
n
Middle Phalanx udi
git
Distal Phalanx n
Distal Sesamoids Lo

Fig.1. Horseforelimbbones(left),thirdmetacarpuspalmarandphotomicrographoftheforamen(middle),andmodulusdistributionalongforamenmediolateralline(right).
Pleasecitethisarticleinpressas:HuangJetal.Bio-inspiredarmorprotectivematerialsystemsforballisticshockmitigation.JMaterDesign(2011),
doi:10.1016/j.matdes.2011.03.061
J.Huangetal./MaterialsandDesignxxx(2011)xxx–xxx 3
Interstitial Intra-osteon
Cement Cement
material
Line line
s
u
Interstitial ul
Material od
M
Intra-osteon
Haversian
Canal
Mediolateral line through aHaversian canal
Fig.2. Featuresoftypicalosteonal-bone(left)andmodulusvariationthroughanosteon.
(plates) phase distributions. Compared to spaced armor designs, fieldwidth,q istheminimumalloweddensity,q isthemax-
min max
the bone-foramen and osteonal-bone designs have functionally imumalloweddensity,q isthefarfielddensity,q (i=0,...,10)
far i
gradedvoidand solidphase distribution, whichismore effective arethefoamdensitycontrollers,andt (i=0,...,10)aretheloca-
i
instrengtheningtheprotectioncapability. tions for the foam density controllers. When q and q are set
9 10
equaltoq ,theabovefunctionssatisfyC1continuityinthenear
far
2.3.Bone-inspiredarmorprotectivematerialsystems andfarfieldsandC1continuityatthenearandfarfieldintersection.
When the values of the density controllers are varied, the Bezier
Design of vehicle armor is based on plate panels. Spaced, flat, curveisupdatedaccordingly.
sloped,orotherarmordesignsareconstructedusingthesepanels.
Therefore,aflatplategeometrywithaspecifiedthicknesswascon- 2.4.Materialdescription
sidered for bone-inspired armor protective material systems for
ballistic shock mitigation. In accordance with the parallels be- A number of metallic foams are suitable for the design of the
tweenbone and engineering designs,a bone-inspired armorpro- bone-inspiredarmorprotectivematerialsystem.Inthispaper,alu-
tective system was constructed using functionally graded foam minum foam from Alulight America was selected and modeled/
materials. The bone-inspired armor plate was divided along its analyzed as typical honeycomb orthotropic crush material [18].
thickness direction into a near field (X ) in the protection side Inthehoneycombcrushmodel,thematerialbehavioriscomposed
n
and a far field (Xf) in the external loading side as shown in ofthreephases:linearelasticloadingwithmodulusEe,volumetric
Fig. 3. The far field has constant density and material properties. crushtostrainecatconstantcrushstressry,andhardeningtofull
Thedensityandmaterialpropertiesvarycontinuouslyinthenear compactionwithmodulusEc.TheparametersEe,ec,andryareex-
fieldandsmoothlybridgeintothefarfield. pressedasexplicitfunctionsofdensitybasedonclosed-cellmetal-
Asthemechanicalpropertiesofafoammaterialdependonits licfoams[16]andmaterialpropertydataprovidedbyAlulight:
density,thebone-inspiredarmordesignproblembecomes:deter- (cid:2)q(cid:3)1:6
minethethrough-thicknessfarandnearfieldfoamdensitydistri- E ¼69 ðGPaÞ ð4Þ
e q
butioncurvessothattheballisticshockresponsecanbemitigated. s
The curve for maximum ballistic shock mitigation is achieved
throughanoptimizationmethod.Duringtheoptimizationprocess, r ¼43:89"0:5(cid:2)q(cid:3)2=3þ0:3(cid:2)q(cid:3)#ðMPaÞ ð5Þ
any density distribution curve could be generated. The following y q q
s s
Bezierfunctionswereemployedtorepresentarbitrarydensitydis-
tributioncurves: " q (cid:2)q(cid:3)3#
8t ¼ i t ði¼0;1;...;10Þ ec¼0:95 1(cid:3)1:4q þ0:4 q ð6Þ
>>>>>>>>>>><ti¼Pi1¼1000(cid:2)ne1air0(cid:3)tisið1(cid:3)sÞ10(cid:3)i ð06s61;06t6tnearÞ whTeroetaqkiesitnhteodaeccnossuitnytatnhdeqstssraisinthreatdeeenfsfeitcyt,oafstthreesssoelindhcaenlclewmaelln.t
>>>>>>>>>>>:qðq0m6in66s6qq1¼¼;0Pqi¼860(cid:2)t616i0q(cid:3)tnqeairsÞiðð1t(cid:3)s6Þ10t(cid:3)i6þtqfarsþ9ðt10Þ(cid:3)9sÞ6qmax 3ccor.ueAsfnfihacinileygnssitstroaefnss1d.o5onptttihmimeeiAszlatuhtliieognhsttaatliucmstirneusms wfoaasmumseadtetroiaml[o1d8e]l. the
min far max near near far
ð3Þ
Agasguntestscenariowassimulatedfortheevaluationofthe
(cid:2) (cid:3)
10
where ¼ 10! ,sisthenormalizedthicknesscoordinate,qis bone-inspiredprotectivematerialsystembyutilizingarectangular
i i!ð10(cid:3)iÞ!
coupon.Inthisscenario,thecouponwasheldwithasteelsupport
thedensityatcoordinates,t isthenearfieldwidth,t isthefar
near far with a central hole for measurement access, and a high-speed
cylindrical projectile was shot towards the coupon front face
(Fig.4).Thecouponisrepresentedbyitscrosssectionedgelength,
Near field tnear nearandfarfieldwidths,aswellasthefarfielddensity,qfarand
mour the near field density controllers q0, through q10 with
tar q9=q10=qfar for continuity consideration. The coupon accelera-
Far field
tionhistoryatthebackfaceinthepenetrationdirectionwassim-
ulatedusingLS-Dyna.Allsimulationswereterminatedatatimeof
15ms.Thecorrespondingshockresponsespectrumwasobtained
through a MATLAB program based on Kelly–Richman algorithm
Fig.3. Nearandfarfieldsforabone-inspiredarmorprotectivematerialsystem.The
arrowrepresentsloadlocationanddirection. [19].
Pleasecitethisarticleinpressas:HuangJetal.Bio-inspiredarmorprotectivematerialsystemsforballisticshockmitigation.JMaterDesign(2011),
doi:10.1016/j.matdes.2011.03.061
4 J.Huangetal./MaterialsandDesignxxx(2011)xxx–xxx
Bone-inspired coupon
High speed projectile
Rectangular steel support
Cylindrical steel support
Fig.4. Modelsforbone-inspireddesignsimulationunderhigh-speedprojectileloadingconditions.
Tocomparetheshockmitigationperformanceofbone-inspired x 105
10
coupons,baselineanalyseswithuniformAlulightaluminumfoam 350 kg/m3
densitiesof 350kg/m3, 419kg/m3, 650kg/m3, 710kg/m3, 980kg/ 9 650 kg/m3
m3, and 1370kg/m3 wereperformed.The maximumacceleration 710 kg/m3
8
vfosa.mdesnasriteydciusprvlaeyaenddinthFeigshs.o5ckanredsp6o.nsespectrafortheseuniform 2m/s) 7 980 kg/m3
For the bone-inspired coupon optimization, the maximum n ( 6
acceleration(maAcc)atthecouponprotectionpoint(backfacecen- o
ter)wasselectedastheobjectivefunction.Thedesignvariablesare erati 5
tthherofuagrhfiqel8d.Tdheensnietya,rqfifearldanddentshietynceoanrtfiroelllderdseqn9siatnydcoqn1t0rowlleerressqe0t k accel 4
equal to qfar to satisfy C1 density distribution continuity require- Pea 3
mentatthenearandfarfieldintersection.Theoverallaverageden-
sity q 6710kg/m3 constraint was used for weight-based 2
average
vehiclemobilityconsiderationsandalldensitieswereconstrained 1
bytheavailablematerialrangeexceptanarrowbandnearthepro-
tectionsidewherethedensitieswereallowedtoreachthevalueof 00 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
the solid cell wall. The optimization problem was found to have
Natural frequency (Hz)
many local optima due to numerical noise. To find a relatively
robust solution, a gradient-based optimization method was Fig. 6. Simulated shock response spectra for uniform Alulight aluminum foam
employedwithmultipleinitialpoints.Thebestpointsarereported couponsatthedensitiesof350kg/m3,650kg/m3,710kg/m3,and980kg/m3.
inthispaper.Theoptimumthrough-thicknessdensitydistribution
curveispresentedinFig.7.Thecorrespondingaccelerationmagni-
tude history and shock response spectrum results are separately
plottedinFigs.8and9.AsummaryisshowninTable1. Protection side Load side
For uniform density coupons, the maximum acceleration
changes only slightly when the density is increased (Fig. 5). In
somecases,arelativedensityincreasegivesrisetoanincreasein
3m) Near field Far field
g/
k
y ( Osteonal-bone pattern
10x 105 ensit
d
m
9 a
o
f
) 8 m
2on (m/s 7 Aluminu
ati 6 Bone-foramen pattern
er
cel 5
ac Through-thickness distance to protection side (m)
m 4
u
m Fig.7. Optimizedbone-inspiredthrough-thicknessfoamdensitydistributionunder
axi 3 theweightconstraintofqaverage6710kg/m3.
M
2
1
themaximumacceleration.Intheshockresponsespectra,increas-
0 ingthedensityincreasesthepeakaccelerationatlowfrequencies
350 413 476 539 602 665 728 791 854 917 980
upto2800Hz(Fig.6).Suchlowfrequencyreactionscanbefatalto
Density (kg/m3)
humans.Thereisnosingleuniformdensityaluminumfoamcou-
pon that can both decrease the maximum acceleration and the
Fig. 5. Simulated maximum acceleration vs. density curve for uniform density
aluminumfoamcoupons. lowfrequencypeakaccelerationsfromtheshockresponsespectra.
Pleasecitethisarticleinpressas:HuangJetal.Bio-inspiredarmorprotectivematerialsystemsforballisticshockmitigation.JMaterDesign(2011),
doi:10.1016/j.matdes.2011.03.061
J.Huangetal./MaterialsandDesignxxx(2011)xxx–xxx 5
x 105 designs utilize the osteonal-bone material design mechanism.
6 Thereisanarrowbandinthestiffregionneartheprotectionside
wherethedensityvariesfrom1370kg/m3tothevalueofthesolid
cell wall. This high density band can be produced by pre-
5
compressing low density aluminum foams or can be replaced by
solidmaterials.
4 unuifnoifromrm A lAulliuglhigt hfto faomam Themaximumaccelerationfortheoptimizedbone-inspiredde-
2) opotipmtiimzeidz ebdo nbeio-i-ninspsipreirded signisonlyasmallfractionofthecorrespondingmaximumaccel-
s
m/ erationoftheuniformfoamdesignofthesameweight(Table1and
c ( 3 Fig.8).Moreimportantly,theoptimizedbone-inspireddesigncan
c
A dramatically reduce the peak accelerations at both low and high
2 frequencies (Fig. 9). The optimization results demonstrated that
minimizingthemaximumaccelerationminimizesthepeakaccel-
erationsoverallfrequenciesintheshockresponsespectra.
1
Due to the high numerical noise in the finite element-based
analyses, the solution from the gradient-based method might be
0 stilllocaloptima.Withamorerobustoptimizationalgorithmsuch
0 0.5 1 1.5 2 2.5 3 3.5 4
asacombinedgeneticandgradientmethod[12],theballisticshock
Time (sec) x 10-3 responseis expectedto be furthermitigatedat a relatively small
averagedensityconstraint.
Fig. 8. Simulated acceleration magnitude histories for the qaverage6710kg/m3
constrainedoptimizedbone-inspireddesignandfortheuniformdesignofthesame
weight(q=708kg/m3).
4.Enhancementofoptimizeddesign
As shown in Fig. 7, the optimized foam density distribution
x 105 shows a very dense, stiff layer on the protection side. Thin steel
platesreplacingtheprotectionsidedenselayerwereinvestigated
6
asenhancementstotheoptimizeddesign.Theenhancedoptimized
bone-inspired design has an average density of 1275kg/m3. The
5 acceleration magnitude histories and the shock response spectra
2) fortheenhanced,theoptimized,andtheuniformdensitydesigns
m/s ofthesameweightareshowninFigs.10and11.
n ( 4 uunnifiofromrm A lAulliughlitg hfota mfoam Theinclusionofathinstiffmetallic(steel)plateintotheopti-
o ooppttiimmizizeedd b bioo-innes-piinresdpired
ati mized bone-inspired design has a particularly effective response
eler 3 forballisticshockmitigation,withthemaximumaccelerationre-
c
ac ducedbynearlyafactoroftenfromtheuniformfoamcouponof
eak 2 thesameweight(Fig.10)andthepeakaccelerationsintheshock
P responsespectrareducedtoverylowlevelsinthefrequencyrange
between10Hzand10,000Hz(Fig.11).
1
5.Experimentalvalidation
0
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Natural frequency (Hz) 5.1.Coupongasgunvalidationtests
Fig.9. Simulatedshockresponsespectrafortheqaverage6710kg/m3constrained Inthegasgunvalidationtests,bothuniformdensityandbone-
optimizedbone-inspireddesignandfortheuniformdesignofthesameweight
(q=708kg/m3). inspired coupons were subjected to the loading of a cylindrical
hardsteelprojectileshotfromagasgunaroundagivenvelocity.
Toreducethefabricationcost,thebone-inspiredcouponswerede-
signed through trade-studies using discrete layers and a small
Theoptimizedbone-inspireddesignsshowfeaturesfromboth
numberofaluminumfoamdensitiestoapproximatethematerial
bone-foramen and osteonal-bone material systems (Fig. 7). The
distributionpatternshowninFig.7.Athinsteelplatewasbonded
optimized designs between the far field and the soft region (the
totheprotectionsidetoenhancetheshockmitigationcapabilityof
lowest density point in Fig. 7) in the near field utilize the bone-
thebone-inspireddesigns.Theuniformdensitycouponshavethe
foramenmaterialdesignmechanism.Betweenthetwostiffregions
same dimensionsas the bone-inspired designmodels. For all gas
(the two relatively high density points in Fig. 7), the optimized
gun tests, the acceleration history in the penetration direction at
a back face point (protection side) was recorded using an
accelerometer.
Table1
Simulated maximum accelerations and average densities for the optimized bone-
inspireddesignincomparisonwiththeresultsoftheuniformdesignofthesame 5.1.1.Gasguntestsetup
weight.
Thegasguntestconfigurationconsistsofagasgun,asteelpro-
Designs Maximum Averagedensity jectile,andacouponclampedbetweenafrontfaceconstraintanda
acceleration(m/s2) (kg/m3) backfacesupportasshowninFig.12.Boththefrontfaceconstraint
Optimizedbone-inspired, 1.97(cid:4)105 708 and back face support were made of rectangular steel plates and
qaverage6710kg/m3 havedimensionsof139.7mm(cid:4)139.7mm(cid:4)9.65mmwithacen-
Uniformdesignwithq=708kg/m3 5.6(cid:4)105 708
tralholeof85.7mmdiameter.Thesteelprojectilehasadiameter
Pleasecitethisarticleinpressas:HuangJetal.Bio-inspiredarmorprotectivematerialsystemsforballisticshockmitigation.JMaterDesign(2011),
doi:10.1016/j.matdes.2011.03.061
6 J.Huangetal./MaterialsandDesignxxx(2011)xxx–xxx
5
x 10
6
uniform, density =708 kg/m3
x uniform, density = 1275 kg/m3
5 optimized bone-inspired,average density=708 kg/m3
x * optimized bone-inspired & enhanced by solid steel,avearge density =1275 kg/m3
2) 4
s
m/
n (
o 3 x
ati x
er x x
el
c x
c 2
A
x
x
1 x
x x x x
* x x x x x x x x
0 * * * * * * * * * ** * * * *
0 0.5 1 1.5 2 2.5
-3
Time (sec) x 10
Fig.10. Simulatedaccelerationmagnitudehistorieswithrespecttotheoptimizedbone-inspireddesign,enhancedoptimizeddesignwithathinsteelplate,and708kg/m3
and1275kg/m3uniformdensitydesigns.
x 105
8
uniform, density =708 kg/m3
X uniform, density = 1275 kg/m3
7 optimized bone-inspired,average density=708 kg/m3
* optimized bone-inspired & enhanced by solid steel,avearge density =1275 kg/m3
6
2)
s
m/ 5
n ( X X
o X
erati 4
cl
c
a
k 3
a
e
P
2
1 * * * * *
* *
0
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Natural frequency (Hz)
Fig.11. Simulatedshockresponsespectrawithrespecttotheoptimizedbone-inspireddesign,enhancedoptimizeddesignwithathinsteelplate,and708kg/m3and
1275kg/m3uniformdensitydesigns.
of12.7mmandaheightof38.1mm.Theshootingvelocitywasde- 5.1.3.Couponfabrication
signedtobe200m/s. Raw 25.4mm-thick aluminum foam plates with densities in
Fig. 13 were ordered from Alulight America, and cut into
5.1.2.Coupondesignundergasguntestconditions 101.6mm(cid:4)101.6mmsize.Thethinsteelmetalplateandthema-
Theoptimizedbone-inspiredcouponhas demonstrateda spe- chinedfoamplateswereassembledusingadhesivematerials.The
cialsoft–stiff–soft–stiffmaterialdistribution(Fig.7).Thismaterial uniform density aluminum foam coupons were fabricated using
distributionpattern wasutilized todesignthe bone-inspired test thesamemethod.
couponsusingdiscretelayersandasmallnumberoffoamdensi- The test coupons were classified into A, B, E, and S groups.
ties.Thecouponwasdividedintofiveregionsalongthethickness GroupSisasampleconsistingoflowandhighdensitiesandwas
direction:Soft1,Stiff1,Soft2,Stiff2,andthinSteelplateasshown usedtoadjusttheelectronicinstrumentandtheprojectilevelocity.
inFig.13.Basedontrade-studiesandtheavailabledensitiesfrom GroupEistheenhancedbone-inspiredcouponasshowninFig.13.
theAlulightwarehouse,thefiveregionaldensitiesforgoodshock GroupAhasauniformdensityof520kg/m3andGroupBhasauni-
mitigationweredeterminedasshowninFig.13.Theaverageden- formdensityof770kg/m3.Higherdensityuniformcouponswere
sityforthisenhancedbone-inspireddesignisabout1320kg/m3. nottestedduetolackofavailablematerial.
Pleasecitethisarticleinpressas:HuangJetal.Bio-inspiredarmorprotectivematerialsystemsforballisticshockmitigation.JMaterDesign(2011),
doi:10.1016/j.matdes.2011.03.061
J.Huangetal./MaterialsandDesignxxx(2011)xxx–xxx 7
Steel projectile
Front face constraint
Bone-inspired or uniform coupon Back face support
Gas gun
Fig.12. Coupongasguntestsetup.
Load Side
m
4 m Soft 1, 470 kg/m3
5.
2
m
6 mm 5.4 m Stiff 1, 850 kg/m3
1. 2
0
1 m
4 m Soft 2, 520 kg/m3
5.
2
m
m Stiff 2, 1260 kg/m3
7
1
Steel plate, 7800 kg/m3
Protection Side
101.6 mm
Fig.13. Enhancedbone-inspiredcouponthicknessdivisionintodifferentregionsandthecorrespondingdensities.
Group E:
Group A: Group B:
=1320 kg/m3
= 520 kg/m3 = 770 kg/m3 average
44% penetration
100% penetration 80% penetration
uniform uniform
bone-inspired
Fig.14. Penetrationsforbothuniformandenhancedbone-inspiredtestcoupons.
Table2
Maximumaccelerationsforbothuniformandenhancedbone-inspiredcouponsforthegasguntests.
Group Aa(uniform) B(uniform) E(bone-inspired)
Firstcentralhit Secondcentralhit 3rdoffsethit
Averagedensity(kg/m3) 520 770 1320 1320 1320
Maxacceleration(m/s2) 3(cid:4)104 6(cid:4)104 1.1(cid:4)104 1.75(cid:4)104 2.3(cid:4)104
a Completepenetrationobserved.
5.1.4.Gasgunvalidationresults the enhanced bone-inspired coupon (Group E) test, a very small
Thetestresultsincludecouponpenetrations,accelerationhisto- maximum acceleration was observed and recorded in the first
riesinthepenetrationdirections, andmaterialflowpatterns.For central hit, but unfortunately the full acceleration history was
Pleasecitethisarticleinpressas:HuangJetal.Bio-inspiredarmorprotectivematerialsystemsforballisticshockmitigation.JMaterDesign(2011),
doi:10.1016/j.matdes.2011.03.061
8 J.Huangetal./MaterialsandDesignxxx(2011)xxx–xxx
x 104 accelerationsarelistedinTable2.Themeasuredaccelerationhis-
6
toriesinthepenetrationdirectionandthecorrespondingshockre-
uniform coupon, density=770 kg/m3 sponsespectraforGroupBandE(secondandthirdoffsethits)are
4 enhanced bone-inspired coupon,second offset hit plottedinFigs.15and16.
2)s * enhanced bone-inspired coupon,third offset hit Theprojectilecompletelypenetratedthe520kg/m3lowdensity
m/ uniformcouponandpenetrated80%ofthe770kg/m3highdensity
on ( 2 * uniform coupon (Fig. 14). The enhanced bone-inspired coupon
elerati 0 * * * * * * * * *** * * ** * p44ro%veodftvheerycoeufpfeocntitvheiciknneressdu(Fciign.g1p4)r.ojectile penetration, to only
cc The experimental results demonstrated that the maximum
s a -2 * * acceleration doubled when the uniform coupon density was in-
axi creased from 520kg/m3 to 770kg/m3. However, the actual
z- maximum acceleration of the 520kg/m3 uniform density cou-
-4
pon might be higher than the recorded value due to the com-
plete penetration. The measured maximum acceleration of the
-6 enhanced bone-inspired coupon is significantly lower than
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
-3 either uniform density coupon result (Table 2 and Fig. 15),
Time (sec) x 10
which is consistent with the previous LS-Dyna analysis results
(Fig. 10).
Fig.15. Gasgunexperimentalaccelerationhistoriesinthepenetrationdirectionfor
theenhancedbone-inspiredandthe770kg/m3uniformdensitytestcoupons. Theexperimentalpeakaccelerationsoftheenhancedbone-in-
spiredcouponinthecorrespondingshockresponsespectrumare
greatly reduced over a wide range of frequencies compared to
the770kg/m3uniformdensitycoupon(Fig.16).
x 104 To investigate the shock mitigation mechanism of bone-
15
inspired armor protective material systems, two tested coupons
werecutacrossthepenetrationhole.Onewasthe520kg/m3uni-
form density coupon from Group A that had full penetration as
2) shown in Fig. 17 (left). The other was the fully penetrated non-
m/s 10 uniform sample coupon from Group S (Fig. 17 (right)) that was
n ( used to setup the facilities. The density distributions of this
atio uniform coupon, density=770 kg/m3 non-uniform sample coupon is shown in the same figure. Other
er enhanced bone-inspired coupon,second offset hit coupons had only partial penetrations and were not cut as they
el enhanced bone-inspired coupon,third offset hit contained hard steel projectile, but some observations could be
Acc 5 made for visible portion. Based on the foam material flow
* * * * * patterns across the cut cross sections, the following important
* observations are obtained:
*
*
0 (cid:2) For both uniform and non-uniform (including the bone-
0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 inspired) coupons, the material flows in both penetration and
Natural frequency (Hz) x 104 lateraldirections.
(cid:2) Uniformdensitycouponshaveamuchmoreuniformpenetra-
Fig. 16. Gas gun experimental shock response spectra for the enhanced bone-
inspiredandthe770kg/m3uniformdensitytestcoupons. tionholesize(Fig.17(left)).
(cid:2) Fornon-uniformcoupons,thedenselayershaverelativelysmall
penetrationholes(Fig.17(right)).
notrecorded.Inasecondattempt,theprojectilewentoutfromone (cid:2) At the interface between low- and high-density layers, the
lateralside.Inthethirdattempt,theprojectilehada1–5%higher foam has more lateral material flow, which contributes to
velocity and some rotation. The penetrations for Group A, B, and the relaxation of the through-thickness shock and load
E(firstcentralhit)areshowninFig.14.Themeasuredmaximum transmissions.
Penetration
Fig.17. Through-thicknesscrosssectioncutsforthe520kg/m3uniformdensity(GroupA,left)andthenon-uniform(GroupS,right)testcoupons.
Pleasecitethisarticleinpressas:HuangJetal.Bio-inspiredarmorprotectivematerialsystemsforballisticshockmitigation.JMaterDesign(2011),
doi:10.1016/j.matdes.2011.03.061
J.Huangetal./MaterialsandDesignxxx(2011)xxx–xxx 9
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Pleasecitethisarticleinpressas:HuangJetal.Bio-inspiredarmorprotectivematerialsystemsforballisticshockmitigation.JMaterDesign(2011),
doi:10.1016/j.matdes.2011.03.061