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.