A THEORETICAL-STUDY OF THE EFFECT OF WELD GEOMETRY PARAMETERS ON FATIGUE-CRACK PROPAGATION LIFE

In the present work, the effect of important butt weld geometry parameters e.g. tip radius of undercut at weld toe, weld toe radius, flank angle, plate thickness and edge preparation angle, and the effect of initial crack geometry on the fatigue crack propagation life have been studied by using Linear Elastic Fracture Mechanics (LEFM), Finite Element Analysis (FEA) and superposition approaches. A simple mathematical model has been developed to predict the co-influence effect of the above-mentioned weld geometry parameters on the fatigue stress range vs life (S-N) curve. This model gives an explanation for the overall effect of weld geometry parameters as the main reason of scatter phenomenon in fatigue testing practice. The predicted scatter band of S-N curves subject to the variation of all the weld geometry parameters is in good agreement with S-N curves covered by design classes from D to W (BS 5400). The design class F which is commonly used for design of butt welded joints has fallen in the middle of the predicted scatter band of S-N curves. It suggests that for the sake of safe design practice class W should be used for fatigue design of butt welded joints instead of class F.