Abstract: A fatigue life prediction method for welding spot defects was proposed based on ultrasonic echo, where the damage coefficient was obtained based on ultrasonic echo characteristics and fuzzy mathematics theory. Then the effects of normal stress, shear stress and initial defects were taken into account，and the corrected average equivalent stress intensity factor through the defect propagation paths was calculated as the evaluation parameters of fatigue life. Through shear fatigue tests for the qualified spot welding joints，small nugget spot welding joints and over burning spot welding joints for the high strength steel-DP600GI, the fatigue life of different welding spot joint defects were compared, and a curve between the corrected average equivalent stress intensity factor and the fatigue life was obtained as the fatigue life prediction curve for welding spot defects. The results show that the curve may effectively predict the fatigue life of the spot welding joints with initial defects, and the proposed method helps to design defect tolerance of resistance spot welding.

Key words: fatigue life of welding spot defect, ultrasonic echo, damage coefficient, corrected average equivalent stress intensity factor

摘要： 提出了一种基于超声回波的焊点缺陷疲劳寿命预测评价方法。该方法采用模糊数学理论，基于超声回波特征获得损伤系数，然后综合考虑法向应力、剪切应力和初始缺陷的影响，将焊点缺陷在裂纹扩展路径上的修正平均等效应力强度因子作为疲劳评价的参量。通过对DP600GI材料的合格焊点、焊核过小焊点和烧穿焊点的接头进行疲劳试验，比较不同缺陷对焊接疲劳寿命的影响，得到一条修正平均等效应力强度因子与疲劳寿命的拟合曲线作为含初始缺陷的焊点疲劳寿命预测曲线，研究结果表明，该曲线能有效预测含初始缺陷的点焊接头的疲劳寿命。该方法有助于合理设计电阻点焊的缺陷容限。

关键词: 焊点缺陷疲劳寿命, 超声回波, 损伤系数, 修正平均等效应力强度因子