Ultimate Strength and Failure Mode of Spot Welds in High Strength Steels

The strength and failure mode of a resistance spot weld between two sheets of steel are shown to be dependent upon the thickness and yield strength of the base material, the diameter of the weld, the strength of the weld metal, and the restraint imposed by the material surrounding the weld. A relationship is developed which makes possible the reliable calculation of the weld diameter required to cause heat affected zone failure around the weld when loaded in shear. It applies to plain carbon steel and the high strength, micro-alloyed steels of up to 690 Mpa (100,000 psi) yield strength. This relationship along with another relating weld failure load to the base metal strength form the basis for a proposed weldability criteria for low carbon steel.