车体底架型材C槽早期断裂分析

Analysis of the premature fracture of U-bar for the underframe of a car body

车体底架与吊装组件通过螺栓紧固连接,吊装组件将导向力与车辆振动载荷通过螺栓传递到车体C槽上,车体C槽发生断裂。通过车辆动力学测试确定极限工况下的载荷,使用有限元法进行校核计算,其运行工况下的静强度最大应力小于材料的屈服强度,在承受交变载荷作用下材料利用率小于1,满足静强度和疲劳强度要求。车体底架型材C槽为铝合金材质,吊装组件材质为高强度结构钢,两种强度差异较大的材质因螺栓紧固扭矩过大,导致C槽配合面塑性变形,在其边缘位置的压痕处形成应力集中区,造成了早期裂纹源萌生,最终车体底架型材C槽疲劳断裂,导致车体吊装组件脱落发生运行故障。

The underframe of car body is bolt-connected with the lifting assembly,and the lifting device transmits the steering force and the vibration load of the railcar to the U-bar through the bolts,which could lead to the fracture of U-bar on the car body.The load in limiting condition is decided with the help of vehicle dynamic test,and verifying calculation is conducted with finite element method,the maximum stress of static strength under operational condition is less than the yield strength of the materials and the rate of material utilization under alternating load is lower than 1,which satisfy the requirements on static strength and fatigue strength.The U-bar on the underframe of the car body is made of aluminum alloy,while the lifting unit is made of high strength structural steel,plastic deformation at the mating surface on the U-bar therefore happens because of the big strength difference of the two materials and the excessive torque out of bolt fastening,consequently the area of stress concentration is formed at the indentation of their edge position,which creates the source the premature crack.As a result,fatigue fracture occurred at the U-bar on the underframe,leading to the fall-off of the lifting device and the operation failure.