vertiy焊接结构疲劳评估教程i聂春戈.ppt

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1、The Mesh-Insensitive Structural Stress Methodfor Fatigue Evaluation of Welded Structures焊接结构疲劳评估的网格不敏感结构应力方法Dr.Pingsha Dong 董平沙董平沙 博士博士Professor and Northrop Grumman Endowed Chair教授 诺斯普 格鲁门荣誉主席Director,Center for Advanced Marine Structures and Fabrication(CAM-SF)先进船舶结构与工艺中心主任School of Naval Architec

2、ture and Marine Engineering海洋结构与船舶工程学院The University of New Orleans新奥尔良大学Training Course 培训教程2006-2009 Pingsha DongAll Rights Reserved目录目录n焊接疲劳基本l相关术语和定义l材料性能的影响l残余应力的影响l几何不连续性的影响l传统方法描述n结构应力方法（I）l结构应力定义与数值实现l焊缝的表示方法l与其它方法（如ASME，IIW等）的比较和示例l结构应力的度量方法与确认n结构应力方法（II）l一般的结构应力计算过程l边界细节的处理l计算实例l多轴结构应力状态的特

3、征l点焊l激光焊l演示/工作流程结构应力后处理器试用版n主S-N曲线方法l基于K的结构应力求解技巧与验证l双态裂纹生长模型与验证l等效结构应力幅参数与验证n基于结构应力的寿命预测过程l失效、焊线定义、焊缝表示方法等l疲劳测试的含义l寿命预测实例n其它应用l焊喉开裂l多轴疲劳l低周疲劳与l热疲劳l电子封装中的焊料疲劳8121631475763717587103115118130135140144158165174185216226234249254268282289Major Awards and Recognitions RecentlyReceived 最近获得的主要奖励与荣誉最近获得的主要

4、奖励与荣誉nIIW 2008 Paton PrizenSNAME 2007 Elmer L Hann AwardnR&D Magazines R&D 100 Award(2006)nTIME Magazine 2005 Math InnovatorsnAviation Week&Space Technology:Aerospace 2004 Laurels AwardnSAE 2004 Weld Challenge:Best Life Prediction WinnernAWS 2004 R.D.Thomas AwardnSAE 2003 Henry Ford II Distinguished

5、 Award for Excellence in Automotive EngineeringnASME 2002 G.E.O.Widera Literature Award,An Overview of Advanced Weld ModelingCapabilities:Fusion Welding先进焊接建模能力概览：熔化焊An Overview of Advanced Weld ModelingCapabilities:Solid Joining先进焊接建模能力概览：固态连接Fatigue of Weldments:Some Fundamentals焊件疲劳：基本知识nSome rel

6、evant terminologies and definitions 一些相关术语和定义nWhats special about weldments?n焊件有哪些特性、n Stress concentration 应力集中n Material properties 材料属性n Residual stresses 残余应力n What decades of research say?近几十年的研究对此的描述n Limitations of conventional fatigue design methods传统疲劳设计方法的局限n What constitutes a good fatigu

7、e parameter?哪些物理量构成好的疲劳参数Terminologies Describing A Typical Welded Joint描述一个典型焊接接头的术语描述一个典型焊接接头的术语nMaterial zones in a joint接头材料区域lBase metal母材（BM）lHeat-affected zonel热影响区（HAZ）lWeld metall焊材（WM）nGeometric locationsn几何位置lWeld toel焊趾lWeld throat/depthl焊喉/焊深lWeld rootl焊根Relevant Fatigue Terminologies a

8、ndDefinitions I 相关疲劳术语和定义相关疲劳术语和定义-InCyclic loading循环载荷nNominal stress at a failurelocation,e.g.,weld crackinto base plate失效位置的名义应力，例如，侵入母材的焊接裂纹处lF/（Wt）lMc/lnNominal stress rangen名义应力变化范围lF/（Wt）lMc/lRelevant Fatigue Terminologies andDefinitions II相关疲劳术语和定义相关疲劳术语和定义-IInMaximum stress最大应力nMinimum stre

9、ss最小应力nStress range应力变化范围（）nMean stress平均应力What s Special about Welded Joints?焊接焊接接头的特殊之处接头的特殊之处Property Heterogeneity材料性质的多样性(母材BM,焊材 WM,热影响区HAZ)Residual Stresses残余应力Geometric Discontinuities几何不连续性Property Variation in Welded Joints焊接接焊接接头材料性质的变化头材料性质的变化Process-induced induced property heterogeneit

10、y焊接过程导致的材料性质的多样性焊接过程导致的材料性质的多样性WM strength mismatch by design焊材强度设计的不匹配焊材强度设计的不匹配Hardenable Steel可硬化的钢材可硬化的钢材BM/WM/HAZ Property Has Little Effect on Fatigue of Welded Joints BM/WM/HAZ的的性质对焊接接头疲劳影响很小对焊接接头疲劳影响很小Comparison of Fatigue Strength between Plain Metal,Notch Bar,and Welded Specimens普通金属普通金属、带

11、缺口金属条与焊接试件之间疲劳、带缺口金属条与焊接试件之间疲劳强度的比较强度的比较Figure 2:Influence of tensile strength on the fatigue strength图图2：抗拉强度对疲劳强度的影响抗拉强度对疲劳强度的影响BM Strengths vs.Fatigue Life(Lewis,2001)母材强度与疲劳寿命母材强度与疲劳寿命(Lewis,2001)TRIP v CMn350 Unwelded Steel TRIP vs CMn350 and Mild Steel Welded Steel 未焊接钢材未焊接钢材 焊接钢材焊接钢材Weld Resi

12、dual Stress Effects on FatiguePerformance:Weld Sequencing焊接残余应力对疲劳性能的影响焊接顺序Pass Sequence Effects on TransverseResidual Stresses焊道顺序对横向残余应力的影响Travel Speed(Linear Heat Input)Effects Transverse Residual Stresses焊接速度(线性热输入)对横向残余应力的影响Restraint Effects on Transverse ResidaulStresses约束对横向残余应力的影响High Restra

13、int Low Restraint强约束 弱约束Residual Stress Distributions in Some TypicalJoint Types一些典型焊接接头的残余应力分布一些典型焊接接头的残余应力分布Then,How to Treat Residual Stress Effects inFatigue Design in Practice?在实际疲劳设计中应如何处理在实际疲劳设计中应如何处理残余应力的影响？残余应力的影响？nConduct controlled fatigue testing采用控制疲劳测试lEffects on applied mean stressesl

14、对施加的平均应力的影响lAs-welded versus stress-relievedl焊态与应力释放nTest specimens must contain representative residualnstress state in structures试件必须包含结构中主要的残余应力状态lSpecimen sizing试件尺寸lResidual stress induced tri-axiality versus“shake-down”Effects残余应力引起的三轴与失稳（？）的影响Model or Specimen Size Must Be SufficientlyLarge t

15、o Quantify Residual Stress Effects模型或者试件模型或者试件的尺寸应该足够大以量化残余应力的影响的尺寸应该足够大以量化残余应力的影响A Butt Joint对接接头Plate joints:w/t=6平板接头平板接头 w/t=6Residual Stress and Joint Constraint Effectson Local Stress/Strain Behavior残余应力和接头约束对局部应力/应变行为的影响Test Specimen Size Requirements forContaining Weld Residual Stress Effect

16、s试件尺寸要求包含焊接残余应力效应Axial Residual Stress轴向残余应力轴向残余应力Tube girth weld length:2.5 sqrt(rt)圆管环焊缝长度:2.5 sqrt(rt)Tubular Girth Weld管状环焊缝Residual Stress Effects on Fatigue Behavior ofWelded Joints-Experimental Evidence残余应力对焊接残余应力对焊接接头疲劳行为的影响接头疲劳行为的影响试验验证试验验证Stress ratio is NOT important应力比并不重要应力比并不重要Stress r

17、ange is important应力幅是关键因素应力幅是关键因素Compressive cyclic loading can be equally damaging压缩循环载荷同样可以引起材料破坏压缩循环载荷同样可以引起材料破坏Recent S-N Data from HHI Mean StressEffects on S-N Behavior HHI的最新S-N数据平均应力对S-N行为的影响Comparison of Fatigue Test Data with DifferentStress Ratio or Mean Stress Effects:As-Welded在不同应力比或平均应

18、力效应下疲劳测试数据的比较焊态Comparison of Fatigue Test Data with Different Stress Ratio or Mean Stress Effects:As As-Welded vs Stress-Relieved在不同应力比或平均应力效应下疲劳测试数据的比较焊态与应力释放Stress Relief Post-Weld Heat Treatment(PWHT)焊后热处理(PWHT)的应力释放nUniform PWHT:Certain magnitude of residual stresses still retained in ideal PWHT

19、n整体热处理：理想的热处理下仍然存整体热处理：理想的热处理下仍然存在一定的残余应力在一定的残余应力nOther treatments such as local PWHT其它处理方式比如局部热处理其它处理方式比如局部热处理lhigher residual stresses retained than uniform PWHT比比整体热处理方式存在更多的残余整体热处理方式存在更多的残余应力应力lhigher residual stresses than as-welded conditions maylresult可能比焊态条件下的残余应可能比焊态条件下的残余应力水平更高力水平更高Observa

20、tions Residual Stress Effects onFatigue小结：残余应力对疲劳的影响nAdequate specimen size is important in fatigue testing to retain representative residual stress states in actual structures为包含实际结构中主要的的残余应力状态，要求进行疲劳测试时要保证足够的试件尺寸nPerhaps,the most significant effects of residual stresses in welded joints:焊接接头中残余应力最

21、重要的影响：（？）lS-N data not sensitive to applied mean load or mean stress S-N数据对施加的平均载荷或平均应力不敏感lStress range serves as a good parameter for implicitly incorporating residual stress effects 应力变化范围是一个包含残余应力效应的很好的参数nWithout adequate control of welding/assembly procedures,any attempts to incorporate residual

22、 stresses in fatigue assessment are futilen对焊接/组装过程没有足够的控制，任何在疲劳评估中考虑残余应力都没有效果nStress relieved conditions:the improvement in fatigue is not Significant 应力松弛条件：对疲劳性能的改善不明显Global Geometric Discontinuities整体几何不连续性GMA weldsGMA焊缝焊缝RSW or plug weldRSW或塞焊或塞焊Laser welds激光焊激光焊Global versus Local Discontinuit

23、ies in Welded Joints焊接接头中的整体和局部不连续性Effects of Geometric Discontinuities on FatigueBehavior in Welded Joints:Unique S-N Curve Slope几何不连续性对焊接接头疲劳行为的影响唯一的S-N曲线斜率Unique features for weldments:焊接件的特性焊接件的特性Different slope from smooth barspecimens光滑试件具有不同的斜率光滑试件具有不同的斜率Unique slope of about 3唯一的大约为唯一的大约为3斜率

24、斜率Different JointGeometries不同的接头几何不同的接头几何Effects of Global Geometric Discontinuities:Well-Defined Failure Modes in Welded Joints整体几何不连续性的影响焊接接头合适的失效模式nDominant Modes:n主要模式主要模式lMode(A)l模式（模式（A）lMode(B)l模式（模式（B）nMode(A)n模式（模式（A）lDesirablel需要的需要的lEasier to analyzel更易于分析更易于分析nMode(B)n模式（模式（B）lLeast desi

25、rablel很少需要很少需要lLarge data scatterl大量数据呈离散性大量数据呈离散性Joint geometr and loading modedetermines which mode dominatesn接头几何和载荷模式决定哪种失效模式接头几何和载荷模式决定哪种失效模式为主为主Joint Geometry Effects on Nominal Stress Rangeversus Cycle to Failure(Weld Toe Failure)接头几何对名义应力变化范围与失效(焊趾失效)循环次数的影响Stress definition:Nominal stress r

26、ange(F/A)应力定义：名义应力副应力定义：名义应力副(F/A)Thickness Effects厚度的影响Loading Mode Effects Tension versusBending载荷模式的影响拉伸与弯曲Implication:Stress Concentration is the Most ImportantParameter Governing Fatigue Life in Welded Joints推论：应力集中是决定焊接接头疲劳寿命的最重要的参数nDominated by geometric and loading conditions取决于几何和载取决于几何和载荷条

27、件荷条件lJoint type/geometry接头类型接头类型/几何几何lLoading mode载荷模式载荷模式lThicknessl厚度厚度l(Weld size,etc)l(焊缝尺寸等焊缝尺寸等)Stress concentration determination:deceptively simplen应力集中的确定：看起来简单应力集中的确定：看起来简单Notch Stress Determination缺口应力的确定n“Kt”only well-defined for a given notch radius“Kf”只在给只在给定缺口半径时才有很好的定义定缺口半径时才有很好的定义lT

28、oo arbitrary to work in practice太随意以至于无法应太随意以至于无法应用用lToo small an element size to be practical太小的单元尺寸不太小的单元尺寸不切实际切实际nLocal notch geometry in welded joints:random in nature焊接接焊接接头中的局部缺口几何：本质上是随头中的局部缺口几何：本质上是随机的机的Notch Radius=?缺口半径缺口半径=?Stress Concentration Behavior at WeldedJoints焊接接头处的应力集中行为nDifficu

29、lties:n一些困难一些困难lSingularity at sharp notchl在尖锐缺口处奇异在尖锐缺口处奇异lArtificial radius:well,too artificiall人为定义的半径：太随意人为定义的半径：太随意Typical SCF determination methodsn典型的确定应力集中因子的方法典型的确定应力集中因子的方法lStrain gauge based measurementsl基于应变片的测量基于应变片的测量Gauge location/size?应变片位置应变片位置/尺寸尺寸Reference position?参考位置参考位置nFinite

30、 element analysisn有限元分析有限元分析lMesh-size sensitivel对单元尺寸敏感对单元尺寸敏感lElement type sensitivel对单元类型敏感对单元类型敏感How About Extrapolation to the Weld Toe Using Surface Stresses Hot Spot Stress(HSS)Methods?将表面应力外推到焊趾位置热点应力(HSS)方法e.g.,an IIW recommended procedure例如，一种例如，一种IIW 推荐的方法推荐的方法(a concept used for offshore

31、 tubular Structures)一种用于船体管状结构的概念Severe element size/type sensitivity!严重的单元尺寸严重的单元尺寸/类型敏感性类型敏感性Surface Extrapolation Based HSS Method When Using Converged Mesh Plate Joints当使用收敛网格时基于HSS方法的表面应力外推板接头 S-N data from the six joint types can be grouped into at least four distinct S-N curves从六种接头类型得到的从六种接头

32、类型得到的S-N数据至少可以归纳为四条不同的数据至少可以归纳为四条不同的S-N曲线曲线Detailed stress calculations:详细的应力计算：详细的应力计算：two distinct types of distributions两种不同的分布类型两种不同的分布类型SCF=?Linear Solid Element Models with Mesh Size 0.1t尺寸约为尺寸约为0.1t的线性实体单元模型的线性实体单元模型Difference in Surface Stress Gradientsbetween Tubular versus Plate Joints管接头和

33、板接头之间表面应力梯度的区别Stress gradients:应力梯度：应力梯度：Tubular joints:more globall管接头：更具整体性管接头：更具整体性Plate joints:more localizedl板接头：更具局部性板接头：更具局部性Distance from Weld ToeSummary:Important Observations on FatigueBehavior in Welded Joints小结：焊接接头疲劳行为的重要结论Fatigue failures follow a few distinct failure modes,e.g.,toe cr

34、ack,throat crack,etc.n疲劳失效遵从几种截然不同的模式，例如，焊趾裂纹，焊喉裂纹等疲劳失效遵从几种截然不同的模式，例如，焊趾裂纹，焊喉裂纹等BM/WM/HAZ properties are not important within a broad class of materialsn对这一类材料来说？，对这一类材料来说？，BM/WM/HAZ 材料属性是不重要的材料属性是不重要的nMean stress effects are not significantn平均应力的影响不显著平均应力的影响不显著nPresence of high residual stresses高残余

35、应力的存在高残余应力的存在nStress range should be used应当使用应力变化范围应当使用应力变化范围nS-N curves exhibit a distinct slope(1/3)nS-N 曲线表现为一个唯一的斜率曲线表现为一个唯一的斜率(1/3)lDominated by crack propagation决定于裂纹扩展决定于裂纹扩展Inherent crack-like discontinuities activated by global stress concentration characteristics at weldsl由整体应力集中导致的内在的类裂纹不

36、连续性焊缝处的特性？由整体应力集中导致的内在的类裂纹不连续性焊缝处的特性？nStress concentration is most important 应力集中是最重要的应力集中是最重要的nLocal notch stress effects(e.g.,weld bead,toe profile,under cuts,etc):random in nature and captured in S-N data 局部缺口应力效应局部缺口应力效应(例如，焊道例如，焊道,焊趾轮廓焊趾轮廓,切割痕等切割痕等):本质上是随本质上是随机的并且可以反映在机的并且可以反映在S-N数据中数据中nA relia

37、ble method is needed for characterizing global stress concentration(overalljoint geometry effect)为反映整体应力集中的特性，需要一种值得信赖的方法为反映整体应力集中的特性，需要一种值得信赖的方法(整体的接头几何效应整体的接头几何效应)Considerations for SCF Characterization对SCF特性的一些考虑Local stresses cannot be readily determined for most practicalapplications对于大多数的实际应用，

38、局部应力并不容易得到 Singular behavior at a sharp notch尖锐缺口处的奇异性Random nature of weld toe/root local details for assuming a definite radius对于假定的一个半径值来说，焊趾/焊根处的局部细节本质上是随机的 Conceptually,there should exist a global stress parameter：理论上来说，应当存在一个整体应力参数：Dominated by overall joint geometry excluding the local effect

39、s排除局部效应，而决定于整体接头几何形状 Load mode,etc.载荷模式等The simplest global stress parameter:nominal stress definition perstrength of material,if applicable最简单的整体应力参数：如果适合的话，名义应力以材料强度来定义A Brief Overview of Conventional Stress Concentration Determination Methods传统的应力集中计算方法简介Global stress parameter based:整体应力参数基于Nomi

40、nal stress名义应力Extrapolation based spot stress基于热点应力的外推Local notch stress parameter based基于局部缺口应力参数Classical Weld Classification Approach Basedon Joint Geometry 基于接头几何的传统焊缝分类方法 Also referred to as“weld category approach”,“cartoonapproach”,“fatigue design rules”(Gurney,1967)也称为“焊缝分类方法”，“图表方法”，“疲劳设计准则”

41、(Gurney,1967)Nominal stress S-N curves(mean and-2)in log-logscale from fatigue tests:由疲劳测试得到的对数坐标中的名义应力S-N曲线(平均和-2)Different joint geometries不同的接头几何 Mostly applicable for weld toe failure mode大部分适用于焊趾失效模式 Limited considerations for weld throat failure modes很少考虑焊喉失效模式Weld Classification Approach:Mean

42、 S-N CurveBS 7608 of(Ref.Plate Thickness:16mm)焊缝分类方法：BS 7608的平均S-N曲线（参考板厚：16mm）A total of 8 S-N curves provided based lab specimen tests实验室试件测试一共提供了8条S-N曲线 Fatigue evaluation procedure:疲劳计算过程 Determine which curve(“B”-“W”)is applicable to a joint of concern确定哪条曲线适合于这种接头 Calculate nominal stress(rang

43、e)per strength of material由材料力学计算名义应力（变化范围）Calculate mean life directly fromthe S-N chart,if constant amplitude loading如果是等幅载荷，直接由S-N图计算平均寿命 Miners rule summation if variable amplitude loading如果是变幅载荷，根据Miner准则进行累积In Practice,A Family of Infinite S-N Curves is Needed,e.g.,IIW s Fatigue Design Recomme

44、ndations(2004)实际应用中，需要一族无限条实际应用中，需要一族无限条S-N曲线，例如，曲线，例如，IIW的疲劳设计建议（的疲劳设计建议（2004）FEA-Based Fatigue Design and Life Prediction基于有限元的疲劳设计与寿命预测基于有限元的疲劳设计与寿命预测Nominal stresses:difficult to extract in most cases名义应力：在大多数情况下难以提取 Cartoon-based S-N curve definitions:difficult to apply基于图表的S-N曲线的定义：难以应用 Soluti

45、on?求解？Almost all research has been focused on how to refinesurface extrapolation procedures几乎所有的研究都集中在如何完善表面外推过程上 The objectives:目标 Reduced the number of S-N curves needed for fatigue design for engineering structures减少对工程结构进行疲劳设计所需的S-N曲线的数量 Improve the mesh-sensitivity in HSS calculations在热点应力计算时改善

46、网格敏感性Extrapolation-Based Hot Spot StressApproach Basic Definition and Assumptions基于外推法的热点应力方法基本定义与假定Developed in 70s for offshoretubular joints发展于70s船体结构的管接头 Used membrane+bendingdecomposition as an argument forexistence of such a stress definition使用膜力+弯曲分解作为这种应力定义存在的证明？Recommends extrapolations usi

47、ng surface stress extrapolationwithout justifying the linkage建议使用without justifying the linkage表面应力外推方法进行外推？Extrapolation positions should be outside of the region dominated by local notch stress外推位置应当在局部缺口应力控制区域之外Surface Extrapolation Based Hot Spot Stress Methods基于表面外推的热点应力方法 Also referred to as:也

48、被称为 Hot spot structural stress热点结构应力 Structural stress结构应力 Geometric stress几何应力 More attractive in principle than nominal stress:从原理上比名义应力更吸引人 Applications where nominal stress cannot be defined应用于名义应力无法定义的地方 Potentially reduced the number of S-N curves needed潜在地减少了所需S-N曲线的数目 Adopted by various fati

49、gue design codes:IIW Recommendations,AWSD1.1,API RP2A,BS 7608,Class Societies Fatigue Guidance,Eurocode,etc.被多种疲劳设计标准采用：IIW Recommendations,AWSD1.1,API RP2A,BS 7608,Class Societies Fatigue Guidance,Eurocode,等 Recent EN 13445,PD5500 etc for pressure vessel and pipingapplications最近在 EN 13445,PD5500 等压

50、力容器与管道标准中得到应用Extrapolation Based HSS Approach(IIW,04)基于外推的热点应力方法(IIW,04)Notch Stress Methods缺口应力方法 Notch stress is ill-defined if assuming sharp notches如果是尖锐的缺口，缺口应力很难定义 Some researchers are investigating the use of notch stress with a fictitious notch radius in FE model一些研究人员正在研究有限元模型中假定缺口半径下的缺口应力的