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本科毕业设计论文I摘要疲劳是指金属材料在应力或应变的反复作用下所发生的性能变化。现代工业中工程结构的可靠性是最基础的要求，工程实际中“疲劳”是引起工程结构件失效的最主要的原因，所以工程结构和材料的疲劳破坏一直是工程设计的重点。镍基高温合金定义为：以镍为基体（含量一般大于50%）、在650~1000℃范围内具有较高的强度和良好的抗氧化、抗燃气腐蚀能力的高温合金。其广泛地应用于燃气轮机的燃烧室、涡轮叶片和涡轮盘，航天器、火箭发动机、核反应堆、石油化工和能源转换设备等的高温部件。在现代飞机发动机中，涡轮叶片几乎全部采用镍基合金制造。本文主要研究了某高温合金在不同应变比（R=0.1，R=-1）和不同温度（室温，600℃，700℃，800℃）条件下的低周疲劳行为以及疲劳特性参数变化特征。重点讨论了温度对某高温合金低周疲劳寿命的影响。研究表明：在两种应变比和三个应力水平下，室温、600和700℃时材料均表现为先循环硬化再循环软化；在两种应变比条件下，800℃时材料在低应变水平表现为先循环硬化，再循环软化。在中高应变水平条件下总体表现为循环软化。Manson-Coffin公式中的参数对温度有很大的依赖性，但其随温度的变化并不单调，大多在700℃左右出现极值。R=0.1及R=-1时，随着温度上升，弹性应变对疲劳性能的影响先减少后增加，在700℃左右时达到最小。R=-1时影响更小些。R=0.1时，随着温度的增加，塑性应变对该材料疲劳性能的影响基本保持不变。R=-1时，随着温度上升，塑性应变对该材料疲劳性能的影响先减少再增加，在700℃左右时达到最小。外加总应变幅以及试验温度对某高温合金的应变疲劳寿命影响均较大，应变比对疲劳寿命的影响则较小。在总应变范围相同的条件下，随着试验温度的升高，疲劳寿命逐渐降低。随着温度的升高，理论疲劳极限先下降再上升，在700℃达到极小值。关键词：镍基高温合金，低周疲劳，疲劳模型，应变疲劳参数本科毕业设计论文IIABSTRACTFatigueisdefinedasthepropertychangeofmetalmaterialsundercycliceffectsofstressorstrain.Inmodernindustry,thereliabilityofengineeringstructureisthemostessentialrequire.Inactualengineeringapplication,themainreasonwhichcausesengineeringstructuresfailureis“fatigue”.Sofatiguebreakdownofengineeringstructuresandmaterialsisalwaysthekeypointofengineeringdesign.Nickel-basesuperalloyisdefinedasthesuperalloywhichisnickelbased(thecontainmentofNiisgenerallymorethan50%)，hashighstrengthandgoodpropertyofantioxidationandresistanceofgascorrosionintherangeof650~1000°C.Itiswidelyusedincombustor,turbinevane,turbineplateofcombustiongasturbine,hightemperaturecomponentinspacecraft,rocketengine,nuclearreactor,petroleumchemistryindustryandpowertransformequipment.Turbinevanesinmodernplaneenginearealmostmadebynickel-basealloy.Thispaperstudiedlow-cyclefatigue(LCF)behaviorandparametervariationoffatiguepropertiesofsomealloysunderdifferenttemperatures(RT,600°C,700°C,800°C)anddifferentstrainratios(R=0.1,R=-1).WespeciallydiscussedtheeffectoftemperatureonLCFlifeofthissuperalloy.Studyshowsthat：MaterialshowscyclichardingfirstthencyclicsoftingunderRT,600and700°Cinthreestrainlevelsandtwostrainratios,showscyclichardingfirstthencyclicsteadyunder，showscyclichardingfirstthencyclicsoftinginlowstrainlevelandgenerallycyclicsoftinginmediumandhighstrainlevelunder800°Candtwostrainratios.ParametersinMason-Coffinformulagreatlydependontemperature，butitisnotmonotonouswithtemperaturevariationandmostofthemreachapeakvaluearound700°C.Transitionlifeofthissuperalloygenerallydecreaseswithtemperatureincreasing.EffectofelasticstrainonfatiguepropertydecreasesfirstthenincreasewithtemperatureincreasingunderR=0.1andR=-1,anditdecreasetoleastataround700°C.EffectofplasticstrainonfatiguepropertykeepwithtemperatureincreasingunderR=0.1EffectofplasticstrainonfatiguepropertydecreasesfirstthenincreasewithtemperatureincreasingunderR=-1,anditdecreasetoleastataround700°CEffectsoftotalstrainamplitudeandtesttemperaturesonthissuperalloyaregreat,andthoseofstrainratiosaresmaller.Underthesametotalstrainrange,fatigue本科毕业设计论文IIIlifedecreaseswithtesttemperatureincreasing,andthetheoryfatiguelimitdecreasesfirstthenincreaseafter700°C,itreachesthepeakvalueataround700°CKEYWORDS：nickel-basesuperalloy,LCF,fatiguemodel,strainfatigueparameter本科毕业设计论文IV目录第一章综述..................................................................................................................11.1引言......................................................................................................................11.2疲劳概述..............................................................................................................11.2.1疲劳研究的背景及意义...............................................................................11.2.2疲劳的分类及影响因素...............................................................................21.2.3疲劳破坏的特点和机理................................................................................41.3低周（应变）疲劳..............................................................................................71.3.1.低周疲劳的研究背景及现状........................................................................71.3.2循环应力应变响应.......................................................................................81.4低周疲劳寿命模型............................................................................................101.4.1.等应变/应力模型......................................................................................101.4.2.基于能量的疲劳模型..................................................................................101.5镍基高温合金....................................................................................................121.5.1发展过程......................................................................................................121.5.2成分和性能..................................................................................................12第二章试验材料及试验方法...................................................................................142.1试验材料及试验设备........................................................................................142.2试验方法...............................................................................