True stress–strain analysis on weldment of heterogeneous tailor-welded blanks—a novel approach for forming simulation

This paper presents a novel experimental method of analysis to determine the tensile properties of weldment of the heterogeneous tailor-welded blank (TWB) and its base metal. A real-time microscopic recording system was developed to acquire the true stress–strain data of the weldment during tensile testing. Specially designed tensile specimens of the weldment were cut from the prepared stainless steel (AISI 304) TWBs with a thickness combination of 1 mm/1.2 mm. With the aid of a newly developed measurement system, the real-time deformation of laser-marked circular grids on the surface of the tensile specimens was captured. The deformation recorded made possible the determination of the stress and strain values of the weldment based on the assumption of plastic incompressibility. The accurately measured tensile data of the weldment is used to determine the localized necking based on the vertex theory. The localized necking criterion is implemented into a computer program, LS-DYNA, which is critical in the numerical simulation of the TWB forming. The simulation makes it possible accurate determination of the strain distributions in TWBs along the centerline perpendicular to the weldment. The predicted strain distributions were compared with those measured and found to be satisfactory, thus demonstrating the validity of the proposed experimental method to accurately determine the true stress–strain values of the weldment and the parent metals.