Influence of mechanical mismatching on the failure of welded joints by void nucleation and coalescence

Based on the modified Gurson model, the changes of void volume fraction, a scalar parameter of damage, were analysed by the finite element method for mismatched welded joint models as well as for two mild steel base metals. Both over matching and under matching of the joints were considered and the width of the weld was varied for each type of mismatching. It was found that the damage of under-matched joints mainly occurred in the sandwiched layer and the damage resistance of the joints decreases with a decrease of the width of the sandwiched layer. The damage of over-matched joints mainly occurred in the base metal adjacent to the sandwiched layer and the damage resistance of the joints increases with decrease of the width of the sandwiched layer. For damage dominated by the strain controlled void nucleation mechanism, it is suggested that a reasonably wide weld is chosen for under-matched welded joints while a narrower weld is chosen for over-matched welded joints.