A J-Integral Approach to Fatigue Resistance of a Tensile-Shear Spot Weld

A J-integral approach was used in this study fco predict the fatigue lives of spot welds subjected to tensile-shear loads. Using a three-dimensional finite element program, J-integral values were computed for spot welds that reflect the overall weld stiffness. Two types of welds were analyzed; conventional solid welds that joined two sheets of low carbon (LC) steel, and annular-shaped welds that resulted from joining a steel sheet to a steel square tube. The latter combination is representative of the joint configuration found in space frame construction.

Fatigue tests were conducted on conventional and annular-shaped welds. The experimental results, together with others found in the literature, were used to define a relationship between a J-integral range (ΔJ) and fatigue life data. It was found that the total fatigue life (N_f) of a weld at one applied stress range is related to its J-integral range such that a ΔJ vs. N_f log-log plot gives a straight line relationship. This relationship holds for different steel gages and weld shapes, and thus can be used to predict fatigue lives of spot welded assemblies where there are multiple welds joining various steels of different gages.