A FATIGUE DESIGN PARAMETER FOR SPOT WELDS

— Mode I and mode II stress intensity factors for two half-spaces connected by a circular patch were used to develop a mixed-mode stress intensity factor (termed the stress index Ki) which can correlate the fatigue life of all spot weld geometries, base metals, and specimen dimensions. Empirical corrections were applied to Broek's equivalent stress intensity factor (Klq) to account for the weldment geometry (sheet thickness, nugget diameter, specimen width) and the effect of mean stress. The final expression, (Ki), is a measure of the notch-root stress field in the location where crack initiation and early crack growth occur. The stress index (ki) should be a useful tool for spot-weld fatigue design.