Failure analysis of CK45 steel crankshaft in light truck diesel engine

Failure analysis was performed on the light truck diesel engine crankshaft made of CK45 steel. Premature failure has been reported in the fillet zones of the main journal-to-crankpin. This study included chemical composition determination, macro and microstructural analysis, mechanical properties evaluation, fractography, and numerical analysis. Fractographic studies using the scanning electron microscope (SEM) identified fatigue as the main mechanism of crankshaft failure. Numerical results showed that the maximum value of stress has occurred in the crack initiation zone. The results of macro measurements showed that the fillet radius was much more than the standard size (r≫0.015d_crankpin). In addition, the hardness results monitored that the main journal surface was slightly reduced to 0.1 mm (550HV difference at 0.1 mm) of induced hardness that a non-uniform distribution of high-slope hardness was observed throughout the cross-section in the main journal. In general, the experimental results showed that the high-slope hardness, the fillet radius more than the standard size, and the presence of stress concentration may be caused the crack to initiate in the fillet zone and thus the cyclic load of combustion pressure has been propagated the crack growth.