Determination of true stress-strain curve for the weldment of aluminum laser-welded blanks

In the automotive industry, the weld quality of aluminum laser-welded blanks (LWBs) is generally assessed by a conventional transverse tensile test. The engineering stress-strain curve, together with other tensile properties (e.g., yield strength, tensile strength, and total elongation) of the monolithic LWBs, can then be obtained by this test. However, LWBs should be considered heterogeneous in structure. The acquired engineering stress-strain curve is therefore unable to represent the tensile behavior of the aluminum LWBs in realistic situations, particularly with regard to the behavior of the weldment. This article presents a novel experimental approach to acquire true stress-strain data on the weldment during the tensile test of LWBs using a real-time microscopic recording system. This new approach will study observations of the real-time deformation of the laser-marked microgrids premade on the surface of the weldment of the LWB. By capturing the deformation of microgrids through the aid of a video encoder and transferring the data for measurement, the localized strains of the weldment can then be computed, and the localized stresses obtained accordingly. Eventually, the true stress-strain curve of the weldment of the LWB can be successfully acquired. In addition, an investigation has been carried out to examine in details the strain distributions of the weldment using the finite element analysis. This was achieved by employing the measured true stress-strain curve of the weldment and reducing the mesh size of the elements to a level that could not be attained via the experiment.