细观和纳观力学的若干进展讲稿-杨卫.ppt

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1、杨卫清华大学工程力学系细观和纳观力学的若干进展2001.9.1-5毫米尺度疲劳断裂量测BiaxialFatigueTesting2001.9.1-5细观显微加载2001.9.1-5纳米尺度疲劳断裂量测2001.9.1-5CM/MD联合模拟Greenfunctionmethodforlatticestatics,Zhouetal.(1992)CombinedCM/MDsimulationbyanoverlappinglayer,Tan&Yang(1994)2001.9.1-5CM/MD联合模拟Adaptive

2、quasi-continuummethod,Phillips&Ortiz(96-99)MaterialPointMethodLattice-MaterialPointMethod,Tan(2000)HierarchicalAdaptiveDynamicSeamlessMulti-scalesTripleidentities2001.9.1-5裂尖位错发射Xing,Dai&YangScienceinChina（2000）initialcracktipcurrentcracktip2001.9.1-5Dislo

3、cationEmissionfromaCrackTip2001.9.1-5多向喷丸引起表面纳米化吕坚与卢柯的喷丸引起表面纳米化实验初始晶粒为50m的铁材料经过喷丸撞击450秒后，表层形成尺寸为10nm的纳米晶粒。2001.9.1-5喷丸引起位错增殖喷丸撞击的二维简化模型实验参数试件表面尺寸：30×35mm2喷丸直径：2mm喷丸数目：300个喷丸速度：5~20m/s喷丸流量：9~90次/(s·mm2)斜入射比垂直入射可引入更高的表层位错密度2001.9.1-5Datainput,timestepselect

4、ionIterationstartsPressure&frictionforceofshot-peensFEMcomputesvelocityandstressfieldsDensityevolutionbydislocationmigrationDensityevolutionbydislocationinteractionTotalchangeindislocationdensityDensityevolutionbydislocationgenerationPlasticstrainratebydis

5、locationmotionChangeinsamplesurfaceprofileAcceleration,velocity,spin&locationofshotsOutputdislocationdensityExititerationFlowChart2001.9.1-5NumericalSimulationParameters:Ironsample:E=2.001011Pa，=0.3，=7.8103Kg/m3Shots:=7.8103Kg/m3Dislocations:b=2.481

6、0-10mHardening–0=200MPa，0=0.1Mobility–VS=2.98103m/s,B=4.001010PaSource–CR=Y,mS=1.00106mm-2Initialdensity–ALL=1.00108mm-2,=1.00106mm-22001.9.1-5NormalImpactDislocationdensityacrossthedepthV/R=20000s-1，＝0,x=0ObliqueImpactDislocationdensityacrosst

7、hedepthV/R=20000s-1，＝20°,x=02001.9.1-5FormingNano-grainsLowanglegrainboundaryGrainboundaryoflargerangleisenergeticallyfavored=10，=2.171011mm-2，D=6.5nm=20，D=13nmLowangleGBformsifqD>2b2001.9.1-5FormingNano-grains初始构型6000弛豫步后2001.9.1-5SuperplasticExten

8、sibilityofNano-grainedMetalsCriticaldislocationspacingis>15~20nminmetalsDislocationsaredepletedinnano-grainedmetalsRoomtemperaturesuperplasticiywaspredicted(Karchetal.,Nature,1987)fornanograinedmetals,butseld