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1、Diss.ETHNo.14314Anonlocaldamagemodelforelasto-plasticmaterialsbasedongradientplasticitytheoryAdissertationsubmittedtotheSWISSFEDERALINSTITUTEOFTECHNOLOGY,ZÜRICHForthedegreeofDoctorofTechnicalSciencesPresentedbyJianChenMasterofEngineering,DalianUniversityofTechnologyBorn:Oct,29,1971,Hunan
2、Province,P.R.ChinaCitizenofP.R.ChinaAcceptedontherecommendationofProf.Folker.H.Wittmann,examinerDr.HuangYuan,co-examinerDr.DietmarKalkhof,co-examinerZürich2001AcknowledgementsTheresearchworkinthisdissertationhasbeencarriedoutatPaulScherrerInstituteintheyear1998–2001.Iwouldliketoexpressmy
3、deepgratitudetoProf.FolkerH.Wittmannforusefulsuggestionsandpatientguidance.IamalsothankfultoDr.HuangYuanwhohelpedmetojoinhisresearchgroupandtobegintheresearchinPSI.Hispatientguidanceforcomputationalformulationsandusefulsuggestionshelpedmetofinishtheresearchwork.ThankstoDr.Kalkhofwhogives
4、meconstanthelpandsupportsinmyresearch.Withtheirguidance,theresearchworkcanbesubmittedtoETHZurich.IamthankfultoallmycolleagesinPSI,especiallytoReichlin,NiffeneggerandKrompholz.SpecialthanksgotoProf.XikuiLiinDalianUniversityofTechnology,P.R.China,whorecommendedmetostudyinSwitzerland.Finall
5、yIwouldliketothankmyFamilyfortheirloveandpatience.AbstractExperimentalandtheoreticalstudieshaveshownthatsizeeffectsinstructuredeformationsandfailurebecomesignificantassoonasstraingradientsarehigh.Forinstanceassoonasmaterialfailuredominatesadeformationprocess,thespecimendisplaysincreasing
6、lysofteningandthefiniteelementcomputationissignificantlyaffectedbytheelementsize.Withoutconsideringthiseffectintheconstitutivemodelonecannothopeareliablepredictiontotheductilematerialfailureprocess.Togiveanaccuratepredictionofthestructureintegrityandtoquantifythematerialfailureprocess,it
7、isnecessarytointroducethestraingradientsintoconstitutiveequations.Gradientplasticitymodelshavebeendiscussedextensivelyinrecentyears.Themesh-sensitivityinnumericalanalysishasbeensuccessfullyeliminatedandanalyticalexplanationsforsizeeffectsweregiven.Inthepresentwork,agenera
