Thecharacterizationmadtestingmethodsofthedynamicfractureinitiationtoughnessofelas-tic-plasticmaterialsundertensileimpactarestudied.Byusingtheself-designedbar-bartensileimpactappa-ratus,anoveltestmethodforstudyingdynamicfracture-initiationhasbeenproposedbasedontheone-di-mensionaltestprinciple.Thecurveofaverageloadv.s.displacement（-δ）issmoothuntilunstablecrackpropagation,andthekineticenergywhichdoesnotcontributetothecrackgrowthcanberemovedfromtotalworkdonebyexternal-forcetothespecimen.Thefracture-initiationpointisdeterminedbycompliance-changingratemethod.Theresultsshowthatthesemethodsarefeasibleandeffective.Throughtheanalysisoftheconversionbetweenworkandenergyofafracturespecimen,thedynamicJ-integralisadoptedasachar-acteristicparameterforelastic-plasticmaterialsunderimpactloading.TheJ-integraliscalculatedfrom-△andP-δcurvesbyusingtheformulaproposedbyRice.TheJ-integralatfractureinitiationisemployedtodescribethedynamicfracture-initiationtoughnessofelastie-plasticmaterialsandtheexperimentalresultsindicatethatJ10canberegardedasamaterialconstant.
