Failure analysis for resistance spot welding in lap-shear specimens

• Failure incidence of resistance spot welding in AHSS lap-shear specimens is explored.
• An analytical solution and the stress distributions near the spot weld are derived.
• The elastoplastic FE analyses are conducted to understand the necking initiation.
• The initial necking failures are located at several angular intervals.

Based on the elasticity theory and finite element method, this paper aims to explore the failure incidence of resistance spot welding in dual-phase lap-shear specimens. The stress function approach is adopted to derive an analytical solution to a lap-shear specimen containing a spot weld nugget subjected to the uniformly distributed loading condition, which provides a means to exploring the stress distributions near the spot weld nugget. The normalized effective stress obtained indicates that the initial yielding failures likely occur at four specific angles of 38.02°, 141.98°, 218.02°, and 321.98° along the spot weld nugget in the lap-shear plate. In addition, the contours of normalized stress are also plotted in the polar system to understand the surrounding stress distributions, which reveals that the locations of the maximum and minimum values of normalized radial, hoop, and shear stresses are located at angles 0°/180° and 90°/270°, 90°/270° and 0°/180°, 135°/315° and 45°/225°, respectively, as the normalized radial distance r/a goes to infinity. The elasto-plastic finite element analysis (FEA) is also conducted to analyze the initial necking or thinning phenomenon. It is found that the angular locations of the maximum equivalent plastic strain or initial necking failure points are located at four angular intervals for the advanced high strength steel (AHSS) plate with a spot weld nugget. The derived stress distributions allow predicting failure behavior and evaluating damage evolution on many engineering structures jointed with spot welds.