Failure analysis and improvement of a 42CrMo crankshaft for a heavy-duty truck

Abstract

The crankshaft of a heavy-duty truck engine fractured and failed. The failure occurred in the left crank web of the seventh main journal. To investigate the cause of the crankshaft fracture failure, macroscopic fracture and microscopic morphological analysis, chemical composition and mechanical properties testing, metallurgical examination and numerical simulation methods were used to analyse the failure of the fractured crankshafts and to propose improvement measures. The results show that the crack source was located at the junction of the threaded bottom hole column surface and taper surface, and the failure mechanism was high cycle fatigue fracture failure. The main reason for the failure was the stress concentration caused by the lack of an obvious transition fillet at the junction of the threaded bottom hole column surface and taper surface, with the maximum stress value of 486.9 MPa. In addition, the metallographic structure transformation of the surface layer of the bottom hole sidewall (maximum depth of about 22 μm) caused by the high machining temperature also had an important influence on the fracture. The proposed improvement scheme of increasing the transition fillet and using an internal cold machining tool was proposed, and the feasibility of the proposed scheme was verified by a fatigue bench test.