简介：Finiteelementmethod(FEM)hasbeenusedtoanalyzethestressandstrainfieldsandthestresstri-axiallevelsaroundthetipofthecrackundermode-Ⅱloading.Theresultsshowthat:undermode-Ⅱloading,thedirectionofthemaximumtensilestressandthatofthemaximumtri-axiallevels(R_)existatanangleof-75.3°fromtheoriginalcrackplane:themaximumshearstressandR_=0existalongtheoriginalcrackplane.Mode-ⅡloadingexperimentusingBHW-35steelatdifferenttemperaturesshowthattherearetwokindsoffracturemode.openingmode(ortensilemode)andslidingmode(orshearmode).Ade-creaseintemperaturecausesthefracturemodetochangefromshearmodetotensilemode.ForBHW-35steel,thiscriticaltemperatureisabout-90C.Actually.underanykindofloadingmode(modeⅠ,modeⅡ,modeⅢormixedmode),therealwaysexistseveralkindsofpotenitalfracturemodes(forexample,openingmode.slidingmode.tearingmodeormixedmode).Theeffectoftemperatureundermode-Ⅱloadingisactuallyrelatedtothechangeoftheelastic-plasticpropertiesofthematerial.