A Fatigue Life Prediction Method for Tensile-Shear Spot Welds
by
Pei-Chung Wang
F. V. Lawrence
Department of Metallurgy and Mining Engineering
Abstract
An empirical Three Stage initiation-Propagation (TSIP) model has been developed which predicts the fatigue resistance of tensile-shear spot welds under constant amplitude loading test. The TSIP model consists of Stage I — fatigue crack initiation and early crack growth, Stage II — through sheet thickness crack propagation, and Stage III — across sheet width crack propagation. The improvements of tensile-sheer spot weld fatigue resistance through manipulation of geometry, residual stress and material property variables are discussed with the aid of the model. The TSIP model suggests that, in addition to the influence of geometry, residual stresses at the site of crack initiation greatly influence the fatigue resistance of tensile-shear spot welds. The TSIP model predicts the subtle role of material properties in determining the fatigue resistance of tensile-shear spot welds.
Tensile-shear spot welds of low carbon and HSLA steel sheet spot welds have been tested to determine the effect of change in nugget shape, preloading and coining post-weld treatments. The effect of these treatments on the fatigue resistance of spot welds was determined using constant amplitude and variable load histories. The experimental results were compared with predictions made using the TSIP model.
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