Truck Diesel Engine Crankshaft Failure Analysis
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TECHNICAL ARTICLE—PEER-REVIEWED
Truck Diesel Engine Crankshaft Failure Analysis Xiao-lei Xu • Zhi-wei Yu • Zhi Yang
Submitted: 2 August 2010 / in revised form: 11 October 2010 / Published online: 11 November 2010 Ó ASM International 2010
Abstract 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. Keywords Crankshaft Fatigue fracture Induction-hardening Failure analysis Hard-rolling
76010 km of operation before failure. The crankshaft is made of C38 steel. The surfaces of crankshaft are required to be induction-quenched and the depth of the inductionhardening case is specified as 2–5 mm. The hardness values of core and surface of crankshaft are, respectively, specified as HV30 250–290 and HRC 50–56.
Experimental Methods The chemical composition of the failed crankshaft material was analyzed by spectroscopy, and the microstructure of the material in various regions was observed by optical microscopy (OPM). The fractured surfaces were observed visually and using scanning electron microscopy (SEM). Macrohardness of crankshaft material and the surface hardness of crankshaft induction-quenched layer were evaluated. Microhardness profiles from the surface to the interior in different regions were made using Vickers system with a load of 1000 g to estimate the depth of the hardened layer. The depth where the hardness values measured are equal to HV1 425 is specified as the depth of the hardened layer.
Introduction It was reported that an abnormal sound was produced by the engine during the operation of a diesel truck. When the diesel engine was disassembled, it was found that crankshaft fracture took place on the first crankpin of the crankshaft. The crankshaft had been in service for X. Xu (&) Z. Yu Z. Yang Electromechanics and Material Engineering College, Dalian Maritime University, Dalian, China e-mail: [email protected]
Observation and Examination Results The failed crankshaft is shown in Fig. 1. It can be seen that the fracture took place at the first crankpin, and the crankshaft broke into two pieces (labeled as parts A and B in Fig. 1). The
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