THE PEAK STRESS METHOD for FATIGUE STRENGTH ASSESSMENT of welded joints with weld toe or weld root failures

The Peak Stress Method (PSM) has been presented in some previous papers, where it was shown that, in plane problems, the singular elastic maximum principal stress, evaluated at the weld toe of fillet-welded joints by means of a finite element analysis, is proportional to the Mode I Notch Stress Intensity Factor (NSIF). In parallel, a model based on the mean value of the strain energy (SED) averaged in a properly defined structural volume surrounding the point of fatigue crack initiation (either the weld toe or the weld root) has been proposed for fatigue strength assessments. The local strain energy values were given as a function of the Mode I and Mode II NSIFs neglecting the influence of the higher order (non-singular) stress terms, In the present work an expression linking the peak stress and the local strain energy value is presented, which can be used in plane problems when Mode II stress fields are non singular (at the weld toe) or of low intensity (at the weld root). By so doing, a single design scatter band valid for either weld root failures or weld toe failures can be calibrated in terms of elastic peak stress evaluated at the critical point.