最新ch2位错-2.4位错与晶体缺陷作用详解教学讲义ppt课件.ppt

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1、ch2位错-2.4位错与晶体缺陷作用详解2.1位错理论的产生一、晶体的塑性变形方式二、单晶体的塑性变形三、多晶体的塑性变形四、晶体的理论切变强度五、位错理论的产生六、位错的基本知识22.2位错的几何性质一、位错的几何模型二、柏格斯矢量三、位错的运动四、位错环及其运动五、位错与晶体的塑性变形六、割阶3Inanalogy,wenextmustconsidertheinteractionofedgedislocations,ofedgeandscrewdislocationsandfinallyofmix

2、eddislocations.Thecaseofmixeddislocations-thegeneralcase-willagainbeobtainedbyconsideringtheinteractionofthescrew-andedgepartsseparatelyandthenaddingtheresults.Withtheformulasforthestressandstrainfieldsofedgeandscrewdislocationsonecancalculatetheresolv

3、edshearstresscausedbyonedislocationontheglideplaneoftheotheroneandgeteverythingfromthere.Butforjustobtainingsomebasicrules,wecandobetterthanthat.Wecanclassifysomebasiccaseswithoutcalculatinganythingbyjustexaminingoneobviousrule:Ifthesuperpositionofthes

4、trainfieldsofdislocationsadduptovaluesofthecompressiveortensilestrainlargerthanthoseofasingledislocations,theywillrepulseeachother.Ifthecombinedstrainfieldislowerthanthatofthesingledislocation,theywillattracteachother.7Thisleadstosomesimplecases:1.Arbi

5、trarilycurveddislocationswithidenticalbonthesameglideplanewillalwaysrepeleachother.82.ArbitrarydislocationswithoppositebvectorsonthesameglideplanewillattractandannihilateeachotherEdgedislocationswithidenticaloroppositeBurgersvectorbonneighboringglidepl

6、anesmayattractorrepulseeachother,dependingontheprecisegeometry.Thebluedoublearrowsinthepicturebelowthusmaysignifyrepulsionorattraction.9ThegeneralformulafortheforcesbetweenedgedislocationsinthegeometryshownaboveisFx= [Gb2/2p(1–n)] · [x·(x2–y2)/(x2+y2)2

7、]Fy= [Gb2/2p(1–n)] ·[y·(3x2+y2)/(x2+y2)2]Fory=0,i.e.thesameglideplane,wehavea1/xor,moregenerallya1/rdependenceoftheforceonthedistancerbetweenthedislocations.Fory<0ory>0wefindzonesofrepulsionandattraction.Atsomespecificpositionstheforceiszero-thiswouldb

8、etheequilibriumconfigurations;itisshownbelow.TheformulaforFyisjustgivenforthesakeofcompleteness.Sincethedislocationscannotmoveiny-direction,itisoflittlerelevancesofar.10Theillustrationinthelinkgivesaquantitativepictureoftheforcesactingo