A Generalized Stress Parameter Approach for Fatigue Life Prediction of Seam Welded Joints

Abstract

This thesis presents a new method, based on fracture mechanics analysis of fatigue, to calculate the generalized stress parameter proposed by Maddox. The generalized stress parameter is computed from the currently existing structural stress definition and the stress intensity factor (SIF) calculation. With the structural stress term accounting for the effect of global weldment geometry, the stress intensity factor captures the local effect of the weld profile, characterized by the weld angle and weld toe radius. Parametric equations for the stress intensity factor are used to obtain the generalized stress parameter. A series of detailed two-dimensional finite element analyses, combined with the weight function method, is employed to validate the effectiveness of the utilized parametric equations. The validity range of these parametric equations is also extended to a wider range, i.e., a larger toe radius, which is more typical for current welded structures in the automotive industry. Finally, the generalized stress parameter is validated with fatigue test results of various specimen types and thickness combinations. It is found that the generalized stress parameter can adequately predict the fatigue life of welded joints and can serve as a better fatigue damage parameter than the structural stress since the weld profile effect has been included.