Failure Analysis of a Train Crank Shaft Under Fatigue Loadings

Failure of parts may happened under the influence of four parameters, design, materials, production process and improper use or combination of these. Therefore, the goal of studying the cause of parts failure is to specify any those parameters and avoid repeating them. Crank shaft is an important component of internal combustion engine that experiences a large number of load cycle during its service life. Crank shaft is subjected to several forces which vary in magnitude and direction. Most of crank shaft fails in cause of fatigue in fillet areas due to bending load. In this research, the failure causes of a train crank shaft were studied using chemical analysis, macroscopic and microscopic investigations by optical and scanning electron microscopes, measurement of journals surface roughness and radius of fillet and mechanical properties. It was found that the cause of failure is fatigue, but a lot of inclusions and probably high roughness and partial decarburizing due to machining have been decreased the fatigue strength.