The crankshaft is a structural component which converts the linear piston movement into rotary motion while the force connecting rod is transformed to torque. Several researchers have been studied on the failed shafts [1–4]. Recently, researchers indicate that mechanical fatigue produced by cyclic bending load on the fillets and steady torsion were probably the most common cause of crankshafts failure [5–10]. Zhang and Yin have investigated a wind turbine main shaft and the results show that stress concentration on the shaft surface are the main reasons that result in fracture of the main shaft. Bugarin has studied two shafts and found that a larger-size fillet can minimize stress concentration in the dangerous sections which shows that the fatigue life can be significantly increased with a simple change in the structural details. Because the fracture failure of the crankshaft can affect the normal work of the machine, the failure analysis of crankshaft have a very important theoretical and practical significance. This paper finds out the cause of the crankshaft fracture through the failure analysis of
the crankshaft (Fig. 1), so as to guide the design and production, improve the fatigue strength and the work reliability of the crankshaft.