Failure Analysis of a Lower Wishbone

It is known that wishbone is a hinged suspension link between the chassis and the suspension hub that carries the wheel. This paper describes the failure analysis of a lower wishbone (control arm) in a light commercial vehicle which had been involved in service loading. The wishbone was analyzed in two ways. In order to investigate reason of the failure, finite element modelling was conducted to evaluate stress distribution and reliability of wishbone. Moreover, the metallographic and hardness evaluation were made on weld seam of the failed part. From metallographic observations, the presence of porosity was found in weld seam. Hardness distributions from the parent material to weld region are measured in the expected range. The results of finite element analysis and metallographic examination showed that the fatigue failure was initiated from highly stressed region in weld seam, and the presence of porosity stimulated crack initiation as well as crack growth.