A method for determining the constitutive model of the heat-affected zone using digital image correlation

The heat-affected zone (HAZ) is an unmelted region of a welded joint that has changed in material properties because of high temperatures during the welding process. HAZ has a lower strength than the base (parent) material (BM) and the weld metal (WM). The lower material strength is more significant if BM is made of high strength steel and the undermatching filler metal is used. Therefore, the constitutive model of HAZ is essential for predicting the mechanical behaviour of the welded joint. In this paper, a method for determining the true stress–strain relationship of HAZ is proposed. The effect of the transverse constraint on the longitudinal deformation of HAZ imposed by BM and/or WM is eliminated by a linear modification factor correlating to the true strain. Standard tensile coupon tests were used to obtain the constitutive model of HAZ using digital image correlation (DIC). The modification factor proposed for reducing the true stress is calibrated based on finite element analysis (FEA). The modified constitutive model of HAZ is validated against the experimental results obtained by DIC. The validated HAZ material property can be used in advanced numerical simulation of welded joints.