Influence of the heat affected zone on the dynamic behavior of a welded joint of armoured steel

Welded joints are often weakened areas due to geometrical stress concentration and heterogeneous materials. This study analyses both the dynamic strain rate sensitivity of materials constituting an armoured steel fillet welded joint: Base Metal (BM), Heat-Affected Zone (HAZ) and Welded Metal (WM), and their influence on the mechanical behavior of such welded joint submitted to impact loadings. Firstly, the quasi-static and dynamic behaviors of the BM, HAZ and WM are characterized and discussed. A specific approach is developed to generate the HAZ material using a thermal treatment. Hardness and grain size are used to validate the replicated HAZ. Secondly, the quasi-static and dynamic true stress-strain relations of the BM, HAZ and WM are determined thanks to a video tracking procedure and a Bridgman-LeRoy correction. It appears that the BM is not rate sensitive from quasi-static up to 1350 s-1. On the contrary, the HAZ appears to be rate sensitive, but by softening. The WM shows a strong viscous hardening. Parameters of Johnson-Cook behavior laws are identified on those three materials by combining a direct method and a reverse engineering approach. In a third part, a Finite Element Analysis (FEA) is led on two welded substructures submitted to impact loading. The comparison with experimental results highlights the added value of implementing HAZ material parameters in the models to better localize the initiation of failure mechanisms.