周風華知識資料知識資料課程輔導(dǎo)資料

課程輔導(dǎo)資料周風華彈塑性本構(gòu)關(guān)系和彈塑性波Elasticwave:Plasticwave:Non-linearelastic/plasticSlopeofstress-straincurvedecreaseswhen1-DwaveequationOxorvEngineeringstrainNominalstressYelasticplastic塑性波的速度取決于硬化模量cpisafunctionofstrain/stressForstress-straincurvesconcavedownwardscpdecreaseasstressincreasesSpecialcaseLinearstrain-hardening(bilinear)Ycc0Y1EEp1突加載荷超過材料的屈服限，產(chǎn)生彈性波和塑性波跨越塑性波的速度、應(yīng)力增量條件：YEEpplasticelasticundisturbedplasticelasticundisturbedSpace-timediagramElasticprecursor遞增載荷作用——持續(xù)的加載遞減硬化（Decreasinglyhardening）

slopereduceswithstrainundisturbedEngineeringstrainNominalstressYelasticplasticelasticwavesplasticwaves(scattered)Monotonouslyincreasingloading遞增硬化（Increasinglyhardening）

slopeincreaseswithstrainFormationofashockwaveundisturbedEngineeringstrainNominalstressYelasticplasticelasticwavesplasticwaves(converged)BABAshockwavefrontO

Man-madecellularmaterials?HexagonalhoneycombsOpen-cellnickelfoambyvapordepositiontechnique??Open-cellpolymerfoamAluminumfoamcoatedbyaluminumskins??Closed-cellpolymerfoamQuasi-staticBehaviorofCellularMaterialsunderUni-axialCompression

AshortstageofelasticdeformationAlongstageofrelativeflatplateaustress(itisgoodforenergyabsorption!)Finally,adensification(i.e.locking)stageWhentherelativedensityincreases,thestresslevelrisesbutthedensificationoccursearlierImportanttonotethatphenomenologicallythestress-straincurveexhibitsaupwardsconcavecharacter1stOrderIdealizationofCellularMaterials:R-PP-LModel

Ingeneral,itisexpectedthat

pincreaseswiththeincreaseof.

Engineeringstress–straincurveofacellularmaterialR-PP-LRigid,PerfectlyPlastic,Locking(R-PP-L)model,onlycontainingtwoparameters:(theplateaustress)and(densification/lockingstrain).Numericalsimulationofahoneycombblockunderimpactloading

TheFEsimulationofhoneycombsunderuni-axialcompressionshowedshockonlytakeplaceonlywhentheimpactvelocityVissufficientlyhighRuanD,LuG,WangB&YuTX:

In-planedynamiccrushingofhoneycombs--Afiniteelementstudy.IJIE

28(2003):161-182V卸載波（Unloadingwaves）

——卸載依存于彈性路線theunloadingdisturbancepropagateswiththeelasticwavespeedtheunloadingwavewillcatchtheprecedingplasticloadingwaveandreducethestressandstrainYEelasticloadingwaveEploadingunloadingplasticloadingwaveunloadingwave追趕卸載RectangularpulseunloadingNoplasticwaveRelationbetweenstressandparticlevelocityRecallingtheequationofmotioniswaveimpedance,afunctionofσ/ε

forelasticwave:yieldvelocity:e.g.,formildsteelForgeneralelastic-plasticmaterial,atthisvelocity,andareacquiredAtultimatestrengthofthematerial,Karmancriticalvelocity:

resultsinfractureY2.2HIGHSPEEDIMPACTOF

ABARONARIGIDANVIL

桿對剛性靶的高速撞擊細長桿對剛性壁的碰撞

（不考慮截面積變化）一次卸載不足以消除塑性QuestionsforDiscussion

(afterChapter2)TwobarswithidenticalL,E,ρbutdifferentY.They