Determination of Johnson-Cook material model for weldment of mild steel

Abstract

The material behavior of mild steel is determined after the material experiences weld induced heating effect. The mild steel, when subjected to high-speed large deformation, is subjected to high temperatures and strain rate. The material behavior is modeled using the Johnson-Cook (JC) model to incorporate the effect of strain, strain rate, and temperature. The material experiences significant metallurgical changes due to the involvement of heat during the welding process. It is thought that the material in the weld zone and the base metal may have different flow stress due to the application of such diverse heat distribution. The mild steel plates of 6 mm thickness are welded using the shielded metal arc welding process. The weld metal pieces are subjected to tensile testing at different strain rates. The JC Parameter for flow stress and strain rate is determined using non-linear regression. The JC parameter for temperature dependence is determined through the heat equation obtained through quasi-static deformation and the data values for the strain rate. The increase of 97 MPa in the initial yield point is observed for the materials in the heat-affected zone (HAZ). The prominent effect is observed in the strain hardening parameter from 0.005 for base metal to 0.06 for HAZ. Later, the tensile test using the finite element model under quasi-static and medium strain rate is simulated incorporating the Johnson-Cook material model for base metal and HAZ of metal. The comparison of tensile load history and material stress–strain curve indicates that the results are in good confirmation with the experimental results for base metal and HAZ.