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1、32013年春研究生《工程材料疲劳与断裂》课程试卷一姓名出生日期年月日性别学校住址民族联系电话现学习院系专业/导师本科学校院系入学时间本科学习专业毕业时间是否学习过以下课程材料科学导论断裂与疲劳其它断裂力学基础结构失效计算机等级外语等级1为什么学习这门课程？和研究课题有什么关系？你同时或稍后还有其它的学习计划吗？2请解释传统的强度设计概念、一般方法及它的优缺点。3你听说或见过有关工程断裂失效的事情吗？请举出一例，并分析它们的力学特点是什么?4什么是金属材料的脆性断裂，它的核心本质是什么？你能说出与之相关的理论观点、术语吗?5
2、什么事疲劳？疲劳有哪些特征？你能画出一个简单的循环载荷示意图吗？6什么是断口分析，在失效分析中断口能提供哪些信息？37疲劳断口和静载破坏断口有什么不同？8已知循环最大应力smax=200MPa,最小应力smin=50MPa,计算循环应力变程Δs,应力幅sa,平均应力sm和应力比R9TheS-Ncurveofamaterialisdescribedbytherelationship,whereNisthenumberofcyclestofailure,Sistheamplitudeoftheappliedcyclicstres
3、s,andisthemonotonicfracturestrength,i.e.,S=atN=1.Arotatingcomponentmadeofthismaterialissubjectedto104cyclesatS=0.5.IfthecyclicloadisnowincreasedtoS=0.75,howmanymorecycleswillthematerialwithstand?10TranslationE2CFatigueCrackNucleationFatiguecracksnucleateatsingulari
4、tiesordiscontinuitiesinmostmaterials.Discontinuitiesmaybeonthesurfaceorintheinteriorofthematerial.Thesingularitiescanbestructural(suchasinclusionsorsecond-phaseparticles)orgeometrical(suchasscratchesorsteps).Theexplanationofpreferentialnucleationoffatiguecracksatsu
5、rfacesperhapsresidesinthefactthatplasticdeformationiseasierthereandthatslipstepsformonthesurface.Slipstepsalonecanberesponsibleforinitiatingcracks,ortheycaninteractwithexistingstructuralorgeometricdefectstoproducecracks.Surfacesingularitiesmaybepresentfromthebeginn
6、ingormaydevelopduringcyclicdeformation,as,forexample,theformationofintrusionsandextrusionsatwhatarecalledthepersistentslipbands(PSBs)inmetals.ThesebandswerefirstobservedincopperandnickelbyThompsonetal.4Theyappearedaftercyclicdeformationandpersistedevenafterelectrop
7、olishing.Onretesting,slipbandsappearedagaininthesameplaces.Later,thedislocationstructureinthePSBswasinvestigatedextensively.Figure14.11(a)showsaTEMmicrographofapolycrystallinecoppersamplethatwascycledtoatotalstrainamplitudeof6.4×10−4for3×105cycles.Fatiguecyclingwas
8、carriedoutinreversebendingatroomtemperatureandatafrequencyof17Hz.Thethinfoilwastaken73μmbelowthesurface.TwoparallelPSBs(diagonallyacrossthemicrog
