FECT

Abstract: A Tensile test of the joined mild steel sheets with spot welding was carried out to investigate the effect of the welding conditions on fracture strength and plastic deformation behavior. The experimental parameters were current and electrode compressive force at the welding part. Maximum force or stress in the sheets was measured, and the deformation and the fracture mode were observed. It is found that there are three types of fracture modes: Interface separation mode (mode I), nugget edge separation mode (mode II), and material and nugget separation mode (mode III). In the latter two modes, plastic deformation near the nugget occurred. The mode I occurred when the current was set low, and the strength was also low. The maximum force range in mode II is wider than in the mode III. In mode III, almost constant high strength was achieved. The tensile stroke to fracture was short in mode I. The maximum force of the welded joint increases almost linearly as the nugget diameter increases and saturates over a certain diameter. The maximum force increases, and the force scattering becomes narrow as the current increases. It was also found that the nugget diameter should not be used for the prediction of the force.
Keywords: welded connection, maximum force, plastic deformation, fracture mode.