汽车扭力梁加强板焊缝裂纹原因分析

Crack Causes Analysis of Automotive Torsion Beam Reinforcement Plate

汽车后扭力梁在四立柱耐久试验进行到规定里程近90%时,发现两处加强板和扭梁焊缝末端有明显裂纹。为找出裂纹产生原因,对两裂纹处进行了断口分析、化学成分分析和显微组织分析,并对该结构进行了仿真模拟受力分析。测试结果表明:一处裂纹起源于加强板和焊缝的未焊合处,另一处起源于加强板和焊缝的热影响区,焊缝裂纹的扩展属低应力疲劳扩展。扭力梁和加强板及焊缝的成分、显微组织、焊缝力学性能分析均满足设计要求;仿真分析表明,焊缝末端集中受力远低于屈服强度,存在未焊合缺陷并且服役应力小的区域先于其他服役受力大的区域先开裂。焊缝裂纹的根本原因是存在未焊合焊接缺陷,及焊接过程中的残余应力作用。

The automotive torsion beam reinforcement plate is found cracks in the weld end in process of four posts durability test,which reach the mileage nearly 90%.The fractrogaphy,chemical analysis,microstructure inspection and the simulation to the structure stress analysis are carried on to find the reason result cracks.It is found that one of the crack caused by incomplete penetration between the reinforcing plate and weld,another crack originated from the feat effected zoon of the reinforcing plate.The results show that chemical analysis,the mechanics performance analysis of the weld are satisfied the design requirements.The stress concentration is far below the yielding strength,the first cracking zone is the place exist the incomplete penetration not the place which withstanding greater stress.The primary cause is the original flaw like incomplete penetration and residual stress appeared in the process of the raw material to the finished product.Both of flows act as the initial fatigue crack in the further fatigue extension.