Effects of biaxial loading and residual stresses on constraint

Abstract

Finite element analyses have been carried out to determine the elastic stress intensity factors, the plastic limit loads, failure assessment diagrams (FADs) and the T- and Q-stresses for each of three postulated defects. The effect of biaxial loading and residual stresses on the stress intensity factor and T and Q-stress solutions, and the effect of weld-base metal mismatch on the plastic limit load were assessed. Results have also been derived for the reduction in constraint with increasing plasticity up to the limit load. For assessments of a narrow mismatched weld of overmatching strength using standard Option 1 or 2 FADs, up to L r =1, this parameter should be determined using the lower strength base material yield strength. The decrease in constraint with increasing L r varies at different positions around the crack front of semi elliptical surface defects. Although constraint is maintained highest just under the free surface towards the ends of the crack, this is generally the region where the stress intensity factor is lowest for tension loading and thus assessments need to take account of both crack tip driving force and constraint.