特种车辆主箱体失效分析

某特种车辆在行驶过程中先后两次发生主箱体故障。采用断口宏微观形貌观察、金相检查、硬度测试和力学性能测试进行了综合分析。结果表明：箱体发生断裂的主要原因是箱体材料变质处理工艺控制不当，导致粗大且呈条片状共晶硅的存在，降低了材料的塑性，使铸件脆性较大；其次铝板处的应力集中与断裂耳轴处的结构存在薄弱环节，在一定程度上加快了箱体的过载断裂失效。通过严格控制变质处理工艺，将断裂处耳轴的轴臂方向朝上与竖直方向呈一定夹角，同时将此处固定座加粗，可有效避免该特种车辆发生类似故障。

Failure Analysis of a Main Box in Special Type Vehicle

A main box in a special type vehicle failed for twice during running. The failure cause was analyzed by micro and macro observation, metallographic examination, microhardness testing and mechanical properties testing. The results show that the fracture of the main box was mainly caused by the decrease of the plasticity of the main box material, resulting from the existence of coarse laminated eutectic silicium, which was caused by improper modification process to the main box material. In addition, stress concentration exists in the aluminium plate and the structure at the fracture position of the trunnion is improper,which promotes the overloading fracture to some extent. The failure of the main box can be avoided by strictly controlling the modification process of the main box material. In addition, by improving the structure at the fracture position of the trunnion and thickening the permanent beat, the reliability and safety coefficient of the main box can be further enhanced. Based on the analysis results, some measures are brought forward to avoid.