Fatigue analysis of spot welds using a mesh-insensitive structural stress approach

This paper describes the application procedures of a nodal force based mesh-insensitive structural stress parameter for analysis of a comprehensive set of spot weld fatigue test data collected from a series of advanced high strength sheet steels. The structural stress parameter is calculated in an equilibrium sense in terms of bending and membrane components from nodal forces and moments at each grid point along the periphery of a weld nugget. Based on fracture mechanics considerations, an equivalent structural stress parameter is then used to take into account the effects of loading mode and sheet thickness on the fatigue of spot welded joints. The equivalent structural stress is proven effective in consolidating the large amount of fatigue data of spot welds for transformation induced plasticity (TRIP), dual-phase (DP), and high strength low alloy (HSLA) steels subjected to both tensile shear and coach peel loadings. As a result, a single master S–N can be established for fatigue design and life prediction of spot-welded structures.