后纵臂的断裂原因分析

Fracture Cause Analysis of a Back Trailing-arm

汽车在试验场行驶21000 km后发现后纵臂断裂,该类后纵臂曾多次发生断裂故障。后纵臂在使用过程中受拉、压、扭等复杂载荷。通过对后纵臂进行外观观察,对其断口进行宏、微观观察,并对后纵臂进行金相组织检查、硬度检查及有限元模拟,确认后纵臂的失效性质,并分析其断裂原因。结果表明:后纵臂的失效性质为疲劳断裂;后纵臂的断裂过程为:在压应力作用下后纵臂中间安装孔处首先发生失稳变形,当后纵臂再次受拉时最大应力转移到中间安装孔处,在交变载荷的作用下发生疲劳开裂。适当增加后纵臂的厚度以提高其刚度,厚度增加后的后纵臂未再发生过类似的断裂故障。

The fracture of the back trailing-arm of a vehicle was found after driving 21000 km in the test site.These back trailingarms were broken for many times.The back trailing-arm was suffering complex loads such as tension,pressure and torsion during operation.Based on observing the appearance of the back trailing-arm,macro and micro appearance observation,metallurgical structure inspection,hardness,finite element analysis and the cause was found.The results showed that the fracture of the back trailing-arm was fatigue fracture.The fracture process of the back trailing-arm was as follows:Buckling deformation occurred at the middle mounting hole of the back trailing-arm under the action of compressive stress.When the back trailing-arm was suffering the tension again,the maximum stress was transferred to the middle mounting hole,and fatigue cracking occurred under the alternating load.The thickness of the back trailing-arm was appropriately increased to improve its stiffness.No similar fracture failure occurred in the back trailing-arm after the thickness was increased.