焊接结构抗疲劳设计新方法与应用

Unique Fatigue Design Method of Welded Structures and Application

与传统金属材料/小尺寸疲劳试样不同,焊接结构具有其独特的疲劳特性:裂纹萌生周期短、疲劳寿命主要消耗在裂纹扩展阶段、焊接结构疲劳具有尺寸效应,这些因素导致了动载荷应力幅值为焊接结构疲劳失效的第一驱动力。基于有限元分析的无网格敏感性结构应力法,可有效描述焊接接头位置的动载荷应力。该方法结合国际疲劳设计标准中S-N曲线族与裂纹扩展速率关系,提出一条能够统一描述不同几何形式、不同板厚接头疲劳行为的Master S-N曲线。该方法在2003年SAE"Fatigue Challenge"焊接结构疲劳预测挑战中获得最准确的结果,并已纳入ASME FFS-1标准等国际标准。结构应变方法则是在结构应力方法基础上提出,可以进一步统一描述不同材料焊接构件的高/低周疲劳性能的疲劳评估方法。该方法采用Master E-N曲线将高周疲劳与低周疲劳分析方法统一。目前此方法已经应用于轨道交通、正交异性桥、重型装备等大型复杂焊接结构的疲劳设计与服役寿命预测中,可量化分析焊接变形、焊缝尺寸、熔透率等因素的影响,实现针对复杂焊接结构/接头的抗疲劳设计。

Different from the lab-scale fatigue coupon,the welded structure has its unique fatigue characteristics.The fatigue life of a welded structure is dominated by the fatigue crack propagation life,while the fatigue initiation period is relatively short.Furthermore,the size of a welded structure also has some influence on its fatigue life,and compared with other factors,the applied stress range serves as the major driven force for fatigue failure.The finite element-based mesh-insensitive traction structural stress can efficiently capture the stress state at the weld location.The family of S-N curves documented in the international standard can be unified into a single Master S-N curve once the equivalent traction stress parameter is used,which is calculated based on traction stress and taking account of the fatigue crack growth behavior.The Master S-N curve can be utilized to capture the fatigue behavior of joints with different geometry and thickness.The method won the 2003 SAE"Fatigue Challenge"competition and has been adopted in the ASME FFS-1 standard.The structural strain method is developed upon the traction structural stress method,which further correlated the high-and low-cycle fatigue data of weldment made from different base metal.The method has been widely used for fatigue design and optimization,fatigue life prediction for the complex welded structure in railway transportation,orthotropic bridge,and heavy equipment,etc.The method can also quantitively analyze the effect of weld distortion,weld size,weld penetration of fatigue life.