焊趾表面裂纹的形态发展曲线与疲劳寿命预测

Crack Aspect Development Curve and Fatigue Life Prediction for Surface Cracks at Weld Toes

以作者建立的焊趾半椭圆表面裂纹应力强度因子数据库以及复杂应力场中焊趾半椭圆表面裂纹前缘应力强度因子分布计算的基本模式法为基础，给出了复杂应力场中焊趾表面裂纹在疲劳扩展过程中形态变化规律及寿命的工程分析方法；并用这个方法计算了一些典型焊接接头在一些典型的外加应力场和残余应力场中的裂纹形态发展曲线。实例计算表明，只有按裂纹扩展的自然途径，即沿着裂纹形态发展曲线来估算疲劳寿命，才能得出正确的结论。对表面裂纹的扩展规律作人为假定来进行疲劳分析，（比如，用线弹簧模型法来分析时，常对裂纹形态比ａ／ｃ的变化规律作人为假定），很可能得出极错误的疲劳寿命预测。

An engineering procedure for estimating crack growth behavior and fatigue lives of semielliptical surface cracks at weld toes in complex stress fields was proposed based on a database of stress intensity factors (SIF) and the elementary modes method developed by author. Then, some examples of crack aspect development curve (CADC) diagrams were calculated through the present procedure for some typical cracked welded joints subjected to some service loading and residual stress conditions. Fatigue lives can be correctly predicted only through integration along the natural crack growth way, namely along the CADC. Some proposed procedures in the literatures, which predict fatigue lives by taking some assumptions to the crack growth way, (for example, those use line spring model and calculate lives by taking assumptions to the variation of crack aspect ratio a/c ), have risks to get very wrong fatigue life predictions. The existence of residual stress and brace plate in a fillet welded joint has obvious effects on CADC and fatigue life.