疲劳统计基础概念资料Word格式.docx

1、 Failure Modes are Different for Static Failure, Low Cycle Fatigue, and High Cycle Fatigue.Concepts in CommonFigure 2: Constant Amplitude Load History.Figure 3: Variable Amplitude Load History.Figure 4: Proportional Multiple Channel Load History.Figure 5: Non-Proportional Multiple Channel Load Histo

2、ry.Fatigue Life and Fatigue Damage疲劳寿命：结构承受载荷至失效所经历的载荷循环数。疲劳损伤：失效的损伤值等于1（累积损伤限），即所有载荷循环造成的损伤是1，其中一个循环造成的损伤称为部分损伤。Miner线性累积损伤准则：总损伤是单个循环造成的部分损伤的线性累积。累积损伤限：通常设为1，可以调整为小于1（偏保守），或大于1。Loading and Local StressesFigure 7: Load Applied to a Component Induces a Nominal Stress and a Local Stress at the Notch.

3、名义应力：伪应力（缺口应力）： 应力集中系数. 影响系数 Figure 8: Pseudo Stress for Non-Proportional Loading.设置影响系数：Geometric Work Sheet， Damage Based Data Reduction MethodsRate Independent Counting Methods基于疲劳的数据缩减方法之间的关系：Figure 10: Derivation of Counting Methods.Data PreprocessingPeak/Valley FilteringFigure 11: Stress-Time

4、History.Figure 12: Peak-Picked Stress-Time History.Hysteresis FilteringFigure 13: Hysteresis Filter.Discretization把载荷幅值范围分成N个等间隔区间（bin），默认值N100。Rainflow Cycle CountingFigure 14: Illustration of a Hysteresis Loop.雨流计数最重要的优势是与疲劳损伤的一致性。雨流计数始于1967年（Endo）。1969年出现程对计数法（De Jonge）。1986年Clormann/Seeger发表了一个变

5、型。还有其它雨流计数的标准方法，如ASTMASTM E1049-85和SAESAE AE-10。LMS Durability Technologies GmbH开发了四点雨流计数法，与法国AFNOR标准相同。The 4-Point AlgorithmFigure 15: The 4-Point Algorithm.Figure 16: Schematic of From-to Matrix Construction.Load Histograms载荷直方图显示载荷循环的幅值和次数，可以显示在SN图上。Figure 17: Time History.Figure 18: Cumulative C

6、ycle Count.Life Curves为了进行whatif分析，LMS定义了寿命曲线和设计点概念。Calculate Fatigue Life设计点（Design point）的默认值是载荷水平（load level）1，载荷水平为k是把载荷放大k倍。Back Calculation of Load Levels给定数据块的次数，求载荷幅值。把设计点的未知量设为Load Level即可。Consecutive Load Histories （Test Schedules）Introduction试验计划由若干信号段编制而成，通常是5至50段信号，重复编排。Fatigue Backgrou

7、nd疲劳损伤依赖于载荷顺序。处理顺序效应的方法有两种：精确法，近似法。LMS Durability Implementation在Method Parameters中，选项Calculate TSD Exact为TRUE（checked）是精确法，FALSE（unchecked）是传统法。只对时间历程信号。Non-Local and Surface Effects基础疲劳寿命数据是用抛光的试验样件进行旋转弯曲试验得到的。实际零件的表面粗糙度，尺寸，载荷类型，以及平均应力水平等因素，都会影响疲劳寿命。The Fatigue Notch Factor只用弹性应力集中系数会导致过于保守的结果。随着作

8、用载荷的升高，有缺口和无缺口零件的疲劳寿命差别将减小。因为局部塑性变形会降低局部应力。因此引入疲劳缺口系数：Figure 19: Comparison Between the Fatigue Behavior of an Unnotched Component Compared to a Notched Component.What are Size Effects?Technological Size EffectsQuenched and Tempered Steel:硬度分布取决于直径，而表面的耐久性极限取决于表面硬度。Figure 20: Hardness Profile in Tem

9、pered or Quenched Steel.High Strength Steel:非金属杂质颗粒的大小，形状和分布影响疲劳寿命。表面越大，出现杂质颗粒的概率越大。Figure 21: Stress Distribution in High Strength Steel Due to Non-Metallic Inclusions.Size Effect of Surface Treatment表面强化的相对深度取决于零件尺寸，并且影响内层的预应力。Figure 23: Different Pre-Stresses at the Inner Layer After Surface Trea

10、tment.How to Account for Size Effects有很多方法，通常是用修正系数调整耐久性极限。Stress GradientsStatistical Size EffectMacroscopic YieldingNeubers Approach to MicroyieldingSummaryConceptCorrection factor Stress gradientAdjustment for macro-yieldingWeakest-link conceptNeubers approach to micro-yieldingSurface Effects表面粗糙

11、度越大，疲劳寿命越短。表面刮痕充当应力集中。Figure 30: Correction Factors Due to Surface Roughness.表面修正系数为.The Statistical Nature of Fatigue疲劳试验结果的分散性，源自材料属性、零件尺寸、工作载荷和制造误差的不同。客户使用情况的差异是最大的。在中、高周区域疲劳寿命差别系数为2并非异常。Figure 31: The Likelihood of Weak Components Subjected to High Loads is Minimized in a Probabilistic Design Ap

12、proach.SN曲线的置信度通常取10%, 50%, 和90%的失效概率。分散度指标是失效概率90%和10%对应的载荷比：Property Influencing FatigueTypical Scatter Manufacturing geometry1.02Material: controlled1.15 welded1.45Applied loads2.00Figure 32: S-N Curve of a Material as Determined from Test Data for the 10%, 50%, and 90% Failure Probability Levels.