最新英汉双语材料力学14教学讲义PPT课件.ppt

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1、英汉双语材料力学14材料力学第十四章交变应力CHAPTER14ALTERNATINGSTRESS§14–1SUMMARY§14–2SOMENOMENCLATUREINTHEALTERNATINGSTRESS§14–3ENDURANCELIMITOFAMATERIALSANDITSTEST§14–4ENDURANCELIMITOFAMEMBERANDITSCALCULATION§14–5CALCULATIONOFTHEFATIGUESTRENGTHOFTHEMEMBERUNDERSYMMETRICCYCLES§14–6SIMPLEINTR

2、ODUCTIONOFMECHANICALPROPERTIESOFMATERIALSATNON-CONSTANTTEMPERATURESANDSTATICLOADS2、Developingprocessofthefatiguefailure:1).Sub-structuresandmicroscopicstructuresproducechangesandthecoreofthepermanentdamageisformed.2).Microcosmiccracksareproduced.3).Microcosmiccracksexpan

3、d、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

4、核。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.（Smoothzoneandcoars

5、ezone）ALTERNATINGSTRESS三、疲劳破坏的特点: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smsminsmaxsaTt

6、sosmt4、Severalspecialalternatingstresses：1).Symmetriccycle：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.sminsmaxsatssmsmsminsmaxALTER

7、NATINGSTRESSoots2.脉动循环：3.静循环：五、稳定交变应力：循环特征及周期不变。交变应力sminsmaxsatssmsmsminsmaxooExample1AboltconnectedtheconnectingwithrodinageneratorissubjectedtothemaximumtensileforceinworkPmax=58.3kN，theminimumtensileforceisPmin=55.8kN.Insidediameterofthewhorlisd=11.5mm，trytodetermine

8、a、mandr.Solution：ALTERNATINGSTRESS[例1]发动机连杆大头螺钉工作时最大拉力Pmax=58.3kN，最小拉力Pmin=55.8kN，螺纹内径为d=11.5mm，试求a、