变速箱拨叉轴断裂失效分析

Failure Analysis of the Transmission Fork Shaft

我公司新开发的某重型卡车变速箱,样箱在进行台架试验时,公里数达到1400 km时发生挂档失效。经拆箱检查发现拨叉轴发生断裂。将断裂零件拆解后,对材质进行化学成分、金相组织、表面和心部硬度分析和检测,对断裂部位进行显微镜观察和扫描电镜观察,最后对拨叉轴断裂部位的受力情况进行有限元分析并与该位置的验算抗疲劳强度进行对比,对断裂拨叉轴进行了失效分析。分析结果表明:拨叉轴断裂形式为低应力拉-压疲劳断裂,造成这一情况的主要原因为零件局部表面组织不符设计要求,另外零件结构设计的不合理也产生了较大的应力集中。最后针对这一问题给出了一些改进的建议和措施。

For a heavy truck gearbox developed by our company,the filing failure occured during the bench test of sample case as the kilometers up to 1400 km. It was found that the fork shaft was broken after the unpacking examination. The chemical composition,metallographic structure,surface hardness and core hardness of materials were analyzed and tested after disassembling the broken parts,and the fracture was observed by microscopy and scanning electron microscopy. Finally,the finite element analysis of the force on the fracture site of the fork shaft was carried out and compared with the calculated fatigue strength of the position. The failure analysis of the fractur fork shaft was carried out. The analysis results show that the fracture mode of fork shaft is low-stress tensile-compression fatigue crack. The main reason for the fracture is that the local surface structure of the parts does not meet the design requirements. In addition,the unreasonable design of parts structure also cause bigger stress concentration. Finally,some improving suggestions and measures are given for this problem.