英汉双语材料力学14.ppt

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1、CHAPTER14ALTERNATINGSTRESSMechanicsofMaterials材料力学第十四章交变应力CHAPTER14ALTERNATINGSTRESS§14–1SUMMARY§14–2SOMENOMENCLATUREINTHEALTERNATINGSTRESS§14–3ENDURANCELIMITOFAMATERIALSANDITSTEST§14–4ENDURANCELIMITOFAMEMBERANDITSCALCULATION§14–5CALCULATIONOFTHEFATIGUESTRENGTHOFTHEMEMBERUNDERSYMMETRICCYCLES§14–6SIM

2、PLEINTRODUCTIONOFMECHANICALPROPERTIESOFMATERIALSATNON-CONSTANTTEMPERATURESANDSTATICLOADS第十四章交变应力§14–1概述§14–2交变应力的几个名词术语§14–3材料持久限及其测定§14–4构件持久限及其计算§14–5对称循环下构件的疲劳强度计算§14–6非常温静载下材料力学性能简介§14–１SUMMARY1、Alternatingstress：Stressatapointinsideamemberischangingperiodicallywithtime.Thiskindofstressiscalledt

3、healternatingstress.FoldironthreadPPALTERNATINGSTRESShigh-pressureoilLow-pressureoil§14–１概述一、交变应力：构件内一点处的应力随时间作周期性变化，这种应力称为交变应力。折铁丝交变应力PP2、Developingprocessofthefatiguefailure:1).Sub-structuresandmicroscopicstructuresproducechangesandthecoreofthepermanentdamageisformed.2).Microcosmiccracksareproduc

4、ed.3).Microcosmiccracksexpand、mergeandformthe“leading”crack.4).Themacroscopic“leading”crackexpandsteadily.5).Thestructurelostsitsstabilityorrupturescompletely.Failureofmaterialsundertheactionofanalternatingstress,incustom,iscalledthefatiguefailure.ALTERNATINGSTRESS二、疲劳破坏的发展过程:1.亚结构和显微结构发生变化，从而永久损伤形核

5、。2.产生微观裂纹。3.微观裂纹长大并合并，形成“主导”裂纹。4.宏观主导裂纹稳定扩展。5.结构失稳或完全断裂。交变应力材料在交变应力下的破坏，习惯上称为疲劳破坏。3、Characteristicsofthefatiguefailure:2).Thehappeningofruptureneedssomenumbersofcycling.3).Thefailureisofthebrittlerupture.4).Theruptureareashowsobviouslydifferentzones.（Smoothzoneandcoarsezone）ALTERNATINGSTRESS三、疲劳破坏的

6、特点:2.断裂发生要经过一定的循环次数。3.破坏均呈脆断。4.“断口”分区明显。（光滑区和粗糙区）交变应力。§14–2SOMENOMENCLATUREINTHEALTERNATINGSTRESS1、Cyclecharacteristics：3、Amplitudeofstress：2、Meanstress：smsminsmaxsaTtsALTERNATINGSTRESSo§14–2交变应力的几个名词术语一、循环特征：三、应力幅：二、平均应力：交变应力smsminsmaxsaTtsosmt4、Severalspecialalternatingstresses：1).Symmetriccycle：

7、sminsmaxsaTsALTERNATINGSTRESSosmt四、几种特殊的交变应力：1.对称循环：交变应力sminsmaxsaTsots2).Fluctuatingcycle：3).Staticcycle：5、Stablealternatingstress：cyclecharacteristicsandthecycleperiodarenotchanged.sminsmaxsatssmsms