Title: Static and Fatigue Strength of Spot Welded Joints of Ultrahigh Strength Steel Sheets.
Abstract:The static and fatigue strengths of ultrahigh-strength steel sheets and ultrahigh-strength steel sheet and lower-strength steel sheet joined by spot welding were investigated. The tensile shear streng...The static and fatigue strengths of ultrahigh-strength steel sheets and ultrahigh-strength steel sheet and lower-strength steel sheet joined by spot welding were investigated. The tensile shear strength of the joint of ultrahigh-strength sheets was lower than the estimated value calculated by estimate equations with the increase in the tensile strength of the base steel, because of the existence of the heat affected zone strength of which was relatively lower than that of the base steel. The tensile shear strength of the joint of ultrahigh-strength sheet and lower-strength sheet depended on the tensile strength of the lower-strength steel. The fatigue strength of the tensile shear mode did not depend on the tensile strength of the base steel. It showed almost a constant value with a change of tensile strength of the base steel. The fatigue strength of the cross tension mode is showed the same tendency as the case of the tensile shear mode. The fatigue strength of the bending mode also showed the same tendency. The fatigue strength did not change with the change of tensile strength of base the steel. But the appearance of fractures were different from each other. Cracks propagated into the ultrahigh-strength side in the case of the tensile shear mode and cross tension mode, but in the case of the bending mode they propagated into the lower strength side.Read More