汽车发动机曲轴断裂分析

汽车发动机曲轴在台架试验过程中突然从连杆轴颈圆角远离扇板一侧边缘发生旋转弯曲疲劳断裂。综合运用断口宏微观观察、表面粗糙度(Ra和Rz)测量、残余应力测试及截面金相观察技术,确定曲轴疲劳断裂主要由轴颈圆角滚压不良导致局部萌生微裂纹及工作过程中受到短时异常应力作用引起;轴颈圆角比技术要求的略小对曲轴疲劳断裂具有促进作用。单一的表面粗糙度Ra不能完好反映轴颈滚压质量,建议采用残余应力测试、表面粗糙度Ra和Rz相结合的方法评价轴颈滚压质量。

Fracture Analysis of Automobile Engine Crankshaft

In the process of bench test, the crankshaft of an automobile engine suddenly suffered from rotational bending fatigue fracture from the round angle of the connecting rod journal away from the edge of the fan plate. Macro and micro observation, surface roughness (R_a and R_z) measurement, residual stress measurement and cross section metallographic observation techniques were used to determine the failure cause. It is found that the fatigue fracture of the crankshaft was mainly caused by the local initiation of microcracks caused by the improper rolling of the journal R angle and the short-term abnormal stress during the working process. The journal R angle is slightly smaller than the technical requirement, promoting the fatigue fracture of the crankshaft. The single surface roughness Ra cannot reflect the rolling quality of the journal, so it is suggested to evaluate the journal rolling quality by the combination of residual stress testing and surface roughness R_a and R_z.