Estimating the Fatigue Resistance of Tensile-Shear Spot Welds
by
F. V. Lawrence, Jr.
P. C. Wang
N. -J. Ho
H. T. Corten
Abstract
An empirical method which is based principally on estimates of the fatigue crack initiation life (NI) 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 NI and thus is founded on the fatigue behavior of smooth specimens and modelling of the fatigue notch size effect. The fatigue notch factor (Kf) required in this analysis was obtained from Pook’s relationships for the stress intensity factors of tensile-shear spot welds. Preliminary results from a three-dimensional finite element elastic stress analysis agree well with the estimates of elastic stress concentration factor obtained using Pook’s relationships. Estimates of NIare added to estimates of the fatigue crack propagation life NP to obtain the total fatigue life (NT) but in the long life regime NP 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.
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