Determination of plastic properties of weld metals using an optimal regression of tensile and hardness test data

•A new optimal regression process for acquiring the weld material properties is proposed by using tensile and hardness test data.•The regression function for the hardness distribution with local softening of weld zone is proposed.•The change in material properties resulting from the change in hardness showed a similar tendency in the two materials used in this study.•The weld material properties of two different pipes were estimated, and showed great accuracy compared to the finite element results and tensile test in terms of load-displacement curve. A new method is proposed to obtain the coefficients of plastic constitutive laws of weld metal via tensile test and hardness test. In this method, a general expression between hardness ratio and flow stress model coefficients is established. The predicted flow stresses for the differential areas are integrated over the entire section of tensile specimen to predict the tensile load. The optimal regression coefficients that minimize the difference between the predicted and experimental loads are derived using the Nelder-Mead simplex direction search algorithm. The constraint for the diffuse necking strain is applied in the convergence procedure to avoid the ‘mystical’ material property shown as non-unique solution. The material constants obtained from the proposed method are independent of the width of tensile specimen. The difference of tensile loads between finite element analysis results using the determined material constants and the experiment was less than 8 %. As the derived material constants were shown to be consistent and reliable, the methodology can be applied to general line welded parts. [Display omitted]