The Mesh-Insensitive Structural Stress Method for 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 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 Architecture 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 pdonguno.edu 2006-2009 Pingsha Dong All Rights Reserved 目录 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 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 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 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 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 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 8 12 16 31 47 57 63 71 75 87 103 115 118 130 135 140 144 158 165 174 185 216 226 234 249 254 268 282 289 Major Awards and Recognitions Recently Received 最近获得的主要奖励与荣誉 IIW 2008 Paton Prize SNAME 2007 Elmer L Hann Award R&D Magazines R&D 100 Award (2006) TIME Magazine 2005 Math Innovators Aviation Week & Space Technology: Aerospace 2004 Laurels Award SAE 2004 Weld Challenge: Best Life Prediction Winner AWS 2004 R.D. Thomas Award SAE 2003 Henry Ford II Distinguished Award for Excellence in Automotive Engineering ASME 2002 G.E.O. Widera Literature Award, An Overview of Advanced Weld Modeling Capabilities: Fusion Welding 先进焊接建模能力概览：熔化焊 An Overview of Advanced Weld Modeling Capabilities: 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 Some relevant terminologies and definitions 一些相关术语和定义 Whats special about weldments? 焊件有哪些特性、 Stress concentration 应力集中 Material properties 材料属性 Residual stresses 残余应力 What decades of research say? 近几十年的研究对此的描述 Limitations of conventional fatigue design methods传统疲劳设计 方法的局限 What constitutes a good fatigue 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 Material zones in a joint接头 材料区域 lBase metal母材（BM） lHeat-affected zone l热影响区（HAZ） lWeld metal l焊材（WM） Geometric locations 几何位置 lWeld toe l焊趾 lWeld throat/depth l焊喉/焊深 lWeld root l焊根 Relevant Fatigue Terminologies and Definitions I 相关疲劳术语和定义-I Cyclic loading循环载荷 Nominal stress at a failure location, e.g., weld crack into 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/l Nominal stress range 名义应力变化范围 lF /（Wt） lMc/l Relevant Fatigue Terminologies and Definitions II相关疲劳术语和定义-II Maximum stress 最大应力 Minimum stress 最小应力 Stress range应力 变化范围（） Mean stress平均 应力 What s Special about Welded Joints?焊接 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 接头材料性质的变化 Process-induced induced property heterogeneity 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 Hardenable Steel 可硬化的钢材 BM/WM/HAZ Property Has Little Effect on Fatigue of Welded Joints BM/WM/HAZ的性质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、带缺口金属条与焊接试件之间疲劳 强度的比较 Figure 2: Influence of tensile strength on the fatigue strength 图2： 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 (Lewis, 2001) TRIP v CMn350 Unwelded Steel TRIP vs CMn350 and Mild Steel Welded Steel 未焊接钢材 焊接钢材 Weld Residual Stress Effects on Fatigue Performance: Weld Sequencing焊接残余应力对疲劳性能的 影响焊接顺序 Pass Sequence Effects on Transverse Residual 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 Residaul Stresses约束对横向残余应力的影响 High Restraint Low Restraint 强约束 弱约束 Residual Stress Distributions in Some Typical Joint Types一些典型焊接接头的残余应力分布 Then, How to Treat Residual Stress Effects in Fatigue Design in Practice?在实际疲劳设计中应如何处理 残余应力的影响？ Conduct controlled fatigue testing采用控制疲劳测试 lEffects on applied mean stresses l对施加的平均应力的影响 lAs-welded versus stress-relieved l焊态与应力释放 Test specimens must contain representative residual stress 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 Sufficiently Large to Quantify Residual Stress Effects模型或者试件 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 w/t=6 Residual Stress and Joint Constraint Effects on 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 for Containing Weld Residual Stress Effects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 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 of Welded Joints - Experimental Evidence残余应力对焊接 接头疲劳行为的影响试验验证 Stress ratio is NOT important应力比并不重要 Stress range is important应力幅是关键因素 Compressive cyclic loading can be equally damag