Fatigue failure of a welded automotive component.

Abstract

Automotive components are commonly tested in fatigue before the final assembly of the vehicle, to ensure the accomplishment of technical specifications of the customer, and to avoid premature failure and accidents with autos. This work investigated the cause of failure of a control arm (component of the automobile movement system), made of high strength and low alloy steel, stamped and welded by robot procedure. The fatigue cracking of the component occurred during the application of standardized blocks of fatigue loading. All standard procedures of failure analysis were applied, with a careful assessment of the material characteristics and the cracked surface. It was concluded that fatigue cracks initiated near the weld bead, at the beginning of the welding procedure. An in-depth analysis of this region showed that there was presence of stress concentration, and the microstructure of the steel has been completely changed, due to an excessive amount of heat at the beginning of the welding. A recommendation to change the welding procedure was performed, ensuring the lifetime specified for the component in the fatigue test.