Failure Analysis of Ductile Iron Differential Housing Spline in 4WD Passenger Car

Abstract

Splines are widely used in mechanical drive systems to transfer rotational motion from a shaft to the gear or from a gear to the shaft. The failure investigation was performed on the differential housing of three different four-wheel-drive car models with gasoline engines. Compilation of failure reports was performed by a first author as a professional car expert from the famous car repair shop in Mashhad city for 6 years. Failure zones appeared on the housing splines after an average operation of 60,000 km. Experiments were performed on two matched members, including the failed ductile cast iron housing and undamaged transfer case shaft of tempered martensite steel. For this purpose, a series of experiments including fractography using scanning electron microscopy (SEM) only for housing and chemical composition, mechanical properties, microstructure, and hardness were performed for both matched members, and finally, stress analysis was performed for two matched members numerically. The results showed that the strength and hardness of the housing material were lower than that of the shaft. Also, striations associated with the teeth flank and face surfaces of the housing using SEM imaging showed that failure was of fatigue type on housing spline teeth.