Thermal effect of the welding process on the dynamic behavior of the HSS constitutive materials of a fillet welded joint

Abstract : Welded joints, due to their manufacturing process, are commonly weakened areas. This study provides a pragmatic methodology to analyze the dynamic behavior of the Base Metal (BM) and the Heat-Affected Zone (HAZ) of an HSS (High Strength Steel) fillet welded joint. Firstly, a specific approach has been developed to generate the HAZ material using a thermal treatment. Hardness and grain size are used to validate the replicated HAZ. This approach appears efficient and repeatable. Secondly, the true stress-strain quasi-static and dynamic behaviors up to failure of the BM and the HAZ have been determined. This characterization was performed thanks to a video tracking procedure and Bridgman-LeRoy correction. The comparison between these two materials shows that the thermal field of the welding process increases the HAZ yield stress and hardening while decreasing the strain at failure. It appears that the base metal is not rate sensitive from quasi-static up to 1350s-1. On the contrary, the heat affected material appears to be rate sensitive, but by softening. This unexpected dynamic material softening requires further analyses. A first Finite Element (FE) numerical analysis on a welded substructure submitted to impact loading shows a strong influence of the HAZ on the initiation of failure mechanisms.