清华大学lesson 12：复习资料

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1、材料科学基础材料科学基础FundamentalofMaterialsFundamentalofMaterialsFundamentalofMaterialsFundamentalofMaterialsProf:TianMinBoTel:62795426，62772851E-mail:tmb@mail.tsinghua.edu.cnDepartmentofMaterialScienceandEngineeringTsinghuaUniversity.Beijing100084ChapterChap

2、terⅣⅣPlasticDeformationofCrystalPlasticDeformationofCrystalLessontwelve§§4.1Introduction4.1Introduction1.DeformationprocessofpolycrystallinematerialsDeformationprocessofindustrialmaterialconsistsofthreestages:�Elastic,whichisreversible�Plasticorperma

3、nt�Fracture2.Deformationmodeofcrystals1)Slip2)Twinning3)Grainboundaryslidingfollowedbyg.b.migration4)Diffusion3.BasicfeatureofslipandtwinningBothslipandtwinningareshearprocessesundershearstresses,i.e.itisatranslationalmovementofoneportionofthecrystal

4、withrespecttotheotheronaspecificplaneandalongaspecificdirection.slipsliptwinningtwinningThemaindifferencebetweenslipandtwinningisthattheformerdoesnotcauseanychangeinorientationinthesensethatanycrystallographicdirectionremainthesamewithrespecttothelab

5、oratorycoordinatesystems.Whilethelatterresultsinchangeinorientation.Aftertwinningthetwopartsofthecrystal,twinnedanduntwinned,aresymmetricaltosomeplaneororientation.Orsay,oneisthetwinoftheother.§§4.2SlipSystems4.2SlipSystems�ⅠⅠ.Definition.Definition：：

6、SlipSystemsisthecombinationofacrystallographicplaneandaτdirectionlyingonit.Ontheplaneandalongthedirectionsliptakesplace.Aslipplaneplusacorrespondingslipdirectioniscalledaslipsystem.τ�ⅡⅡ.Slipsystemsoftypicalcrystals.SlipsystemsoftypicalcrystalsFCC:S.S

7、.(SlipSystems)is{111}<110>atR.T.(temperature).Thereare12S.S.inall.HCP:S.S.{0001}<1120>+{1010}<1120>formetalswithlargec/aforotherHCPmetalsBCC:{110}(0001)formetalswithlargec/a{112}<111>{1010}+<1120>{123}{1011}forotherHCPmetalsCsCl:{110}<100>�ⅢⅢ.Schmid.

8、Schmid’’slaw(Theconditionforslaw(Theconditionforsliptostart)sliptostart)1.Theshearstressactingonslipplanealongslipdirectionis.τFcosλFτ==cosλcosφ=σµ�∧AAλ=(F,S.D.)oocosφ�∧�φ=(F,n)σ:normalstress�λ+φ≠90µ:orientationfactorµ=0.5maxSlipoccurswhentheresolved