Crack Analysis Of A Gasoline Engine Crankshaft

In this study, failure analysis of a crankshaft was carried out. The crankshaft made of nodular graphite cast iron was used in a gasoline engine. The cracks propagated axially on surface of the 4th pin journal. Microscopic observation was conducted on the surface of journals. Mechanical and metallurgical properties of the crankshaft including chemical composition, micro-hardness, tensile properties and roughness were studied and compared with the specified properties of the crankshaft materials. As a result of the analyses, the main reason of failure was determined as thermal fatigue because of contact of journal and bearing surface. This condition leads to the formation and growth of fatigue cracks. The contact is probably resulted from defective lubrication or high operating oil temperature. In addition, the contact caused scratches on surface of the 4th pin journal and 5th main journal.