nCode培训实用疲劳理论

ESmMttfig tM Unc|veSWY-.Oai y 2 MTCAxt * 2!hr 匕wyxijt cc* n;兀 0r祠 Od2 50比禺 t!C3i 伽 A如畑为他卫ZACMfbuortrwn; taco biua ai a reonlrwol Hmtr UrKmr sf Ums tens Mifcr tr EretMttcn Hu!rq)crt araf aod t mezi Uig belMcrtf tteotdoeirCWrEI-immMrMR疲劳失效位错滑移和阶段一裂纹扩展在美国已经得到确认，由于产 品的疲劳问题所引起的损失占 国尺生产总值的4%左右（约 1200亿美元）.中国机械工程手册在第6章結 构疲劳强度设计”中指出：机 械零构件80%以上为疲劳* 坏，冈此対承受循环栽荷的 零构件祁应进行疲劳强度设计.疲劳失效所涉及的领域汽车.航天.航空、航海、能源、国防.铁路、海洋工程及-般的机器制造等工业领域4工盘车国訪*MMX夕9MITT*机春裂纹起始和扩展Formabon of a crack causes local stress concentration at the crack tip. The area ahead of tlie crack is now undergoing cyclic plastic deformation.5疲劳寿命定义裂纹起始寿命O|=O裂纹扩展寿命O总寿命OO”1 7；*役力谨应变疋HI平如应力- The bigger the range the faster the failure- Tensile mean accelerates fatigue-Fatigue life reduces xponentiatty wvth rang*- Compressive mean retards it- Viewed concpg to keep rt ciosed影响疲劳寿命的其它因素应力集中表面加工表面处理尺寸效应加帥、波形对室温疲劳影响很小Hitchhikers Guide to the Galaxy7怎样预测疲劳寿命?How fatigue life is predicted?ESmmatof CMnCode1871 q Wohler苗北HtMJM：*进fj了廉统的馥労研九 发展了置转疔曲被芳试怕S4曲线及建育极礙槪念.疲劳发展简史nCode疲劳发展简史(1/2)Wohler曲线和疲劳极限疲劳发展简史(2/2)劳祐环次fb 1839年.Poncelet拎先便用疲劳-诃. 1849铠 英园机械工程学会(IMechE)辩论结晶理论 1864年.Fairbairn用交变戏荷对船链进行了实般 1871 q . Wohler疗先对铁路乍紬进行了系统的疲劳研究.发展了旋转弯曲枝劳试阶.SN曲线及戒劳极限概念 1886年.Bauschinger fi先确证力W变淘冋线 1903年.Ewing和Humphrey证明结M理论是不正确的.折出疲劳足由J型性变形所引起 1910年.Bairstow-lVtr.变循环中的W力应变响应.提出了循环硬化和循环软化概念 1920年.Griffith研究了玻璃中的裂纹山此诞牛了断裂力学 1955年. 1959 年. 1964 年. 1968 年. 1981 年. 1982年 2002年.Manson和Coffin研处仆V变条件控制卜的彼芳. 热狐坏、低周疲劳及哩性应受问题。Pans忤先提出种用斷裂力学参数处理 裂纹扩展的方法。Neuberg议了 种方法.估计W力集中处的弹皺性应力应变。Matsuishi和Endo提出了雨流循环计散方 能够进行合理披劳计口的计“机紂片发展。 nCode国际Aftt公司成立，丿F发和销售披劳寿命 侦测软件.捉供疲劳咨询服务nCode推出了 ICEGow疲劳软件9经典疲劳寿命预测技术iiCodeZn7三种基本的疲劳寿命估计方法 SN （总寿命法）名义应力或弹性应力和总寿命之间的关系 eN （裂纹起始寿命法）局部应变和裂纹起始卷命之间的关系 LEFM （裂纹扩展存命法）应力强度I人I子和裂纹扩展速率Z何的关系这空方法依檢）柑級性!Nf=Ni + Np名义应力法S-N局部应变法（e-N）斷裂力学法LogNf总好命试样和实际零件的差别通常没有应力集中表而光洁度一定通帘不进行衣面处理尺寸一定常幅加载均值不变（通常为0）有应力集中表面光洁度多样农而町能经过处理尺寸不同通常为变幅加戦均值变化 /Q11局部应变(e-N)法AK-da/dN曲线定义同样的局部应变.同样的裂纹起始寿命!对付低周疲劳知Z尸195年.Paris育先録出了 一种用断裂力儒 歩8(处理5?紋扩展的方法！循环应力应变和应变寿命曲线定义裂纹扩展寿命法同样的应力强度因子.同样的裂纹扩展速率!疲劳寿命预测-我们需要什么？疲劳分析5框图Fatigue Life13应力循环定义/载荷种类疲劳载荷nCodeEBmmatetg tM Unm|t4d2S/S- A = S./Sj 磊Parameters required to define a stress cycle:1 Q C1 pmax min or2 Sm. Saor3. ASV RNote that:6.895 xksi MPa应变循环定义nCe*3. Ac, CminBlockLoadingVariableAmplitudeLoadingConstant AmplitudeMonotonic LoadingTlmt.tEngine IngAEngnetrlnoSfrMnEnomertno atrvcc - Strain Curv*0.002(SETencMoFmoturetr. a.Engineering Strain. %EJonotlonxooL A.HReduotlon In Art* “”100True Stress True Strain Curve(Trw stress -tram)Iktw IStrain Valia only up to neoklno 15疲劳寿命的统计性质r ( f JiQRcn-mp 二dMtnbuuoa of LfcSofter inS-N疲劳寿命预测法S-N疫劳试脸nCodeZn7“工程是一种近似对而不是完全错的艺术Engineering is the of being approximately right rather than exactly wrong引h英国Sheffield大学Rod A Smith Ct授的话.1990年QB你能得出一个受等幅对称 交变应力钢棒的疲劳寿命 吗？Wohler曲线和疲劳极限S-N疲劳寿命预测法Stress-based Fatigue Life MethodnCodeAST17小测验平均应力影响实验结果图SN疲劳试验The Relationship between Su & Se#小测验平均应力影响实验结果图#小测验平均应力影响实验结果图小测验：答案 Specimens are subjected to 8nstant amplitude loading The number of cycles to failure is plotted against the nominal elastic stress on a log-log plot and the best fit curve computed There are standards Curves can be derived forsmooth specimens, individual : components, sub-assemblies I or complete structures I ?irCWjSN疲劳试验#小测验平均应力影响实验结果图 SN曲线玻劳极限成活冶 c Surface treatments ere used toto indue* pre-oompression ininduce residual surfacethe surfacestresses.Nitridmg- Heat up component in an ammonia environment. The component expands and Nitrates from the gas react with the metal The component contracts on cooling and is compressed.Effect of Residual Compression小测验答案1)Resulting surTac stress rwvn got. into tension therefore surface crack doesnt mitiiteSurface CompreMionStressOtcttating bendingStressThis effect only works for high cycle cases where the applied surface stress is insufficient to overcome the residual pre-compression.试验获得光湄试样的SN|lll线根据材料极限强度和农向彩响内子 的经验关系将光滑试样的SN曲线 修正到一般机加匸表面的S4I曲线根期应力范川从修正过的SN曲线 得出疲劳寿命值25小测验答案2加载型式影响试验获得一般机加工表而的S-Nllll 线根据应力范IM从-般机加【衣Mis. N曲线直接得出嫂劳寿命值叫07（穹曲到拉伸）mbt 工0.58转）Typically :irCe/S-N疲劳寿命预测法加栽型式形响nCode小测验答案.受等幅对称拉伸应 立钢棒的疲劳寿命 短！WW小测验你知道i个受等幅 对称弯曲应力和一 个受等幅对称拉仲 应立钢棒的疲劳寿 命哪一个长吗？S-N疲劳寿命预测法尺寸形响nCode27小测验小测验答案受等幅対称弯曲应 力小钢榕和去钢棒 的疲劳寿命哪一个 长！ri尺寸影响Larger volume at high stressr r./ H受等幅对称弯曲应 力小钢棒的疲劳寿 命长！#小测验小测验答案S-N疲劳寿命预测法缺口修正和应力集中系数nCode#小测验小测验答案 Mechanical Engineering Design. J E. SNgiey & L.O. Mheli. 4* Ed. McGra-MUl. 1983小测验S-N曲线修正#小测验小测验答案/rC*/q29应力集中系数疲劳强度降低应力集中系数疋义ar氐痕劳强度降低票效ivcwiQ缺口弓I起应力集中理论弹性应力集中系数,Ktrl rVrQ Stress CcrKentraoon Factors R. E. Peterson. Jonn Whey. New Yodc. 1974工程中的应力集中k b0 O/O04020.d 8864SCyclet. NKf depends on: Geometry Dimensions Mode of loading Material type Kfts usually less than K,缺口敏感性性应子(q)Kr is usually less than Ktwhere 0q1ifq-0 then K,-1ifq-1 then Kr-K,(No notch effect) (Ful notch effect)Empirically1q丿 R/TC4NQwherer is notch root radius a i material constantSN曲线缺口修正利用疲劳缺口系数 Kf(Ne)和 KHN=1000)对 SN 曲线进行修正或利用应力集中系 数Kt对S-N曲线 进行修正.这种修 正足僞安个的！For wrought ferrous alloys31#Accounting for NotchesLOo.eK；-1 06kTTTEluZ0BOO200JOOJl0332!00*-AM*Jvw0294466 Sy細 SOSS Strain ano strength. R C. JuvMl. McGraw Hll. New Yam. 1967 Mechanicai Bena-.-or of Matenas engneenng mecnocs for aeTorrtion. fracture ana Tatigue Norman E. Doling Prenttceiai. 1993小测验答案S-N疲劳寿命预测法变幅栽荷处理nCodeZn7变幅载荷你预估出一个受交变应力 钢棒的疲劳寿命吗？ SN tests are conducted under constant amplrtude sinusodal loading Real loading rs usually fairly random-AAAAA/ The quesbon is bow do we break down real loads mto equivalent cycl ranges so we can um the same SN curves9 The is done using Rainflow Cycle Countingr雨流计数法/rC/rQ线性累积损伤，没有考虑加载顺序!WH碧命是多少个載祈信号玄复块疲劳试验获取材料S-N曲线 调整SN曲线.对应力进行雨流计数疲劳寿命计算小测验答案Step 1准备小试样做等幅対称应力控制疲劳试验8SIMM小测验答案Step 2获取材料S-N曲线37小测验答案irCMStep 3调整S-N曲线* -缺口 一表面加1. -表面处理 -尺寸#小测验答案S-N疲劳寿命预测法总结回顾nCode#小测验答案影响疲劳寿命的因素#Step 5对毎个循环计算疲劳损伤 用Minerii则累积总损伤计算疲劳寿命+N八AS = 450) N2S = 50) Afz(A5 = 100)总拥伤值应力幅值平均应力应力築中表面加工衣面处理加我方式尺寸牧应加载频率.波形对室温疲劳形响很小#/rCrZ-Q#S-N曲线法思路SN方法特点总结39S-N曲线法思路SN方法特点总结7从试样中测出材料的SN曲线彩股实际寥件和试样的圣别修止SN曲线考色试验加我和实“加疲的区别应用甬流技术对应力信号进行循环周计数納介Miner损伤斛积法则计紀枝芳乔金S-N曲线法（名义应力法）是以交变名义应力 为主要參量预测字部件疲劳失效循环周效 的一种经验方法基于（名义）应力用丁预测总冯命广泛应用j加载应力水平低、循环次数高（大丁1E4TE5）的高周疲劳失效问题 有关这种方法的大量材料数据可以获得 不适用令显著刻件应变的疲劳问越 广泛用丁焊接件方法简单、易理解#S-N曲线法思路SN方法特点总结#S-N曲线法思路SN方法特点总结irCt/rQStress-Based Fatigue Analysis一些专业术语 Cycle En dura nee limit Failure cyde nu mbers Notch effect Stress range and stress Surface finish and surfaceamplitudetreatment Mean stress Fatigue damage Nominal stress Miners rule Rain flow cycle counting Repeats (fatigue life) Stress concentration factor Fatigue strength reduction factorfc “S-N疲劳分析流程#S-N曲线法思路SN方法特点总结Tutorial: SN Hand Calculation#S-N曲线法思路SN方法特点总结#S-N曲线法思路SN方法特点总结nCodeSSmmatwtf tw U#41Tutorial: SN Hand Calculation/rCr/rQe-N疲劳寿命预测法Local Strain ApproachnCodefESithe Uwt严Tutorial: SN Hand CalculationStrain-Life OutlineOverviewLoadingMaterial characterization Mean stressLocal geometrySurface finish and treatment Vanable amplitude loading Damage accumulation Stress-strain trackingTutorial: SN Hand CalculationLow allov steel wwa = -9751 =-0.087孚;(2对-A.00 IM 111 11： ai JK4 It： M 11? Ill M Life (Cycle:)同样的局部应变.同样的裂纹起始寿命!r 、/ K1#43Some Basic Strain-Life ConceptsStrain Control vs. Stress ControlMMSmooth apedmtn rproducaioclzd puabcityelMtlc bodyTypically: engmeemg cracks are 2-5 mm long cracks initiate in a smooth specimen and at the root of a notch g equal numbers of cycles bcafcwd dtformabon r$，oca，ttedp，ast，cfty stra.nontrolled() crack growth is not considered,i material rather than 8mponentbehavior is being simulatedMaterials CharacterizationnCode Strain Control uses an extensometer in the servo control loop. Stress Control is actually load control Strain Con trol controls total strain, which In dudes plasbc strain the parameter that causes fatigue damage. Stress Control controls the wrong parameter. Stress and Strain are only Bequivalenr, i.e. linearly related, un der purely elastic conditio ns i.e. when there should nt be any fatigue damage.循环应力应变和应变寿命曲线应变控制试验 Test carried out to ASTM E606 High quality test specimen Polished surface Precislon machined for minimum surface residual stress Strain monitoring using high quality clip gauge#应变控制试验结果循环硬化和软化Ifthen material wll cyaidy naroen tf 2 i : then mateciai will cycidy soften/TlfV E应变寿命曲线Confidence of Survivalio1!010/it !grtvxl from tucctMlw 献rain ilf tette art plotted on tM strairvLirt curve elasbc Irfe line given by: s. -(2N,f plastic life line given by : sr - s*(2Nr )9 total We line given by : #(2Nf；(2N, )*Typical values:E - 207.000StMlft)1300 MPa0M0 5C * -0.5循环应力应变曲线nomlna iifeihe:.告ie.z-090% INtM： s护H W r；(2H f 心仪It. Z-1.28nominal ltf-llneRrtrMs io fanurttoStrain-Based Cyclic ParametersStrain-Life Parametersessans 60- fabgue strength coefficient:G*f fatigue strength exponent: b fatigue ductilrty coefficient:s*r fatigue ductilrty exponent: c1300 MPa standard error of log(se):se(st) -* 0.03 standard error of log(sp):se(s J * 0.06strain, log plastic strain, epCyclic Stress-Strain Parameters cydic strength coefficient: K* cydic strength exponent: n* modulus of elasticity :E*1200 MPaJ 205.000 MPa (Steel)45Estimating Strain-Life Parameters47#Steelsa；1.5UTSb-0087；0.59c-0.58Aluminum & Titanium1.07UTS-0.0&50.35-0.69Other Alloys1 OUTS-0.120.7GDoi-0.8Accounting for Mean Stress1.65 UTS0.151.G1UTS0.11#/i CodethNote: -1 if 罟S0.003 others” eJ.35珂罟Q：#考虑平均应力A cycle is defined by its range, 工，and its mean strain,A A/But what is its mean stress?rm / time CJSCTeCa*#Tutorial II: EN Hand Calculation滞回环曲线近似(Masings Hypothesis)两倍1环曲力应费曲钱2c/1耳应力strain, #49Bauschinger, Material Memory & CyclesCycles cloeed :1: BCB2: ADA#Morrows Approach As plasticity increases the effect of mean stress decreases The effect can be taken into account by consider!ng only the elastic-life line Similar to Goodman method in S-N警（2叫）4 吓;（2NJ72010.AISI 4340 StM 轨=1172 MPaSWT Mean Stress Correction#io1 忡 io4 io1 io1 ioT2M Rtvtrtait to taiiurtMorrow平均应力修正Local GeometryiiCodenM#Smith Watson Topper ApproachNotches Cause Stress Concentratioris#Kt depends on: Geometry Dimensions Mode of loading理论弹性应力集中系数,Kt Strew Concentration Factors. R. E Peteon. John Wiley. New YorK. 1974mGjacreca* SWT parameter is an extension of Neubefs Rule This parameter collapses all the mean stress data onto a single curve.J,普（2NF+SE；（2N,广 Assumes that the material parameters are compatible. That is K* and n* are derived from 昭 5： c and bSingle curve describesthe effect of mean stress#工 JOTJeJ s-%wcscooAccounting for Surface Finish &TreatmentnCodea?0.1 Swm Strain Strtngtn. R C.McGraw him. n“ Yom. 1967IMCMCToCfl*The Effect of Surface Finish/rlZrQOf000 K)0 IK) 140 M BO XX) 770 740 TIM)S. Ultimate Tensile Strength. MNotch Sensitivity FactorKt is usually less than Kfwhere 0q1if q-0 then Kr -1 jfq1 tMn Kr.K,(No notch effect) (RjII notch effect)EmpiricallyFor wrought ferrous alloysIwfwrtf a -r It notch root radlut11 FI E matenai constantJ0T5IU 8vpn$ WK.-1Neuberg Rule: K/Se=aenominal etraln . nominal tw SElMilOe-fNtuMr Pro