Truck Diesel Engine Crankshaft Failure Analysis

A diesel engine crankshaft fractured in service after 76010 km of operation. The fracture took place on the first crankpin, and the fracture surface has a 45° inclination with respect to the axial. The results indicate that fatigue is the dominant failure mechanism of the crankshaft. It was observed that the fatigue crack initiated at the fillet region of the first crankpin-web. This crankpin is the one among the six crankpins which bear operational load. Absence of the induction hardening case in the fillet region decreased the fatigue strength and led to fatigue initiation and propagation in the weakened region. Although hard-rolling process was conducted in the fillet region, the depth of hard-rolling layer was insufficient to produce the desired residual compressive stress in the fillet region, and therefore the fillet could not offer resistance to the applied load. In addition, the presence of network-like ferrite in the microstructure facilitated the fatigue crack to be initiated and propagated.