An Empirical Method for Estimating the Fatigue Resistance of Tensile-Shear Spot Welds

An empirical method which is based principally on estimates of the fatigue crack initiation life (N_I) has been developed which predicts the fatigue resistance of tensile-shear spot welds in the long life regime. The method uses Basquin’s law and Peterson’s equation to estimate N_I and thus is founded on the fatigue behavior of smooth specimens and modelling of the fatigue notch size effect. The fatigue notch factor (K_f) required in this analysis was obtained from Pook’s relationships for the stress intensity factors of tensile-shear spot welds. Estimates of N_I are added to estimates of the fatigue crack propagation life N_P to obtain the total fatigue life (N_T) but in the long life regime N_P can usually be neglected. The improvement of tensile-shear spot weld fatigue resistance through manipulation of geometry and material property variables are discussed with the aid of the model. The model predicts that nugget diameter, sheet thickness, and residual stress control offer the best possibilities for fatigue life improvement.