某乘用车副车架台架疲劳试验裂纹成因分析

Analysis on the Causes of Fatigue Crack Formation in Sub-frame of Passenger Car

某乘用车副车架在以企业标准进行疲劳试验的过程中多次出现疲劳裂纹。对副车架极限工况下的受力状态进行有限元分析,发现裂纹出现的位置应力集中比较明显。对副车架极限工况下的受力使用应力应变电测试验分析,在误差允许的范围内试验与分析结果可相互印证。由于裂缝位于焊缝或焊缝周边位置,无论有限元分析或电测实验均无法有效诊断焊接缺陷导致的应力集中,遂对副车架进行金相试验分析遂使用金相试验分析副车架的焊接质量。金相试验显示副车架确存在焊接缺陷。试验分析说明：在该副车架几处焊接位置处存在明显的应力集中,且焊接本身存在焊接缺陷为疲劳试验副车架裂纹产生的原因。

A passenger car subframe generated fatigue cracks repeatedly in the fatigue test process based on the enterprise standard.The finite element analysis of the subframe under the extreme condition shows that the location of the crack has the obvious stress concentration phenomenon.The electrical measurement experiment is used to analyze the force of the subframe under the limit condition. The test result and the analysis result can be mutual corroborated within the error tolerance. As the cracks in the welding or around the welding,Both finite element analysis and electrical measurement experiment can not effectively diagnose the stress concentration which was caused by welding defects,then using metallographic test analyses the subframe welding quality. Metallographic tests show that there is a welding defect in the subframe.Both stress concentrations which are obvious in several welding positions in the subframe and the welding defects are the cause of the cracks in the fatigue test.