Fatigue-reliability analysis of resistance spot-welds

The resistance spot welding process has been widely used in the automotive industry for decades. Once the vehicle weight reduction by down-gaging sheet metal and down-sizing reinforcements becomes of importance, the fatigue performance of spot welds will be a critical factor in design and analysis. Since most of the existing analytical approaches are still deterministic and too complicated to use, this paper presents a simple deterministic model for spot welds under tensile-shear type of loading and a reliability-based model for design and analysis criteria. The simple model is developed on the nominal stress around the weld, defined as the ratio of the load per weld to the net cross sectional area. The load per weld can be easily calculated from any FEA codes with rigid elements for the spot welds. Also, the reliability spot-welded fatigue model is derived on the assumption that the fatigue life and the stress amplitude follow the Weibull and Beta distributions, respectively. Several examples are illustrated to determine the design stress amplitude, the useful fatigue life and the probability of failure. Moreover, the database for the statistical fatigue properties of spot-welded specimens in tensile-shear tests are generated for the reliability analyses