Effect of plate deformation around the nugget during tensile test on tensile shear strength of resistance spot welded lap joints

Abstract

Resistance spot welding is used in automobile body assembly. Tensile shear test is one of the strength evaluation methods for welded joints. Generally, in tensile shear tests of lap joints, rotational deformation occurs in the joint due to offset of the load axis. In this paper, the effect of rotational deformation of resistance spot welded lap joints on tensile shear strength was investigated. A high-strength steel plate HT590 was used. First, tensile shear tests were conducted using only resistance spot welding (Normal) and a specimen in which the welded joint part was sandwiched between two steel blocks to suppress rotational deformation. For the specimens sandwiched between steel blocks, a specimen was prepared with a constrained point parallel (P) to the tensile direction and a specimen with a constrained point vertical (V) to the tensile direction. And the length of the steel blocks was varied in five ways for the tensile shear test. The results showed that the tensile shear strength increased as the length of the steel block increased. However, the suppression of rotational deformation didn’t have a significant effect on tensile shear strength. In tensile shear tests of lap joints, opening of the lap plates occurs in addition to rotational deformation. Therefore, tensile shear tests were conducted using a specimen with two steel blocks sandwiched at the edge of the lap to suppress the opening of the plates. The experiment was reproduced and investigated by FEM analysis. The results showed that the tensile shear strength increased in the deformation-suppressed specimens compared to Normal specimens. In other words, it is clear that the suppression of plate opening has an effect on the increase in tensile shear strength. The above results indicate that suppression of plate opening is effective in increasing tensile shear strength.