Predictions of elastic-plastic crack driving force and redistribution under combined primary and secondary stresses - Part 2: Experimental application

Engineering components may contain small crack-like defects that experience combinations of primary and secondary stresses during service. A new function, g, was introduced in the accompanying Part 1 paper to quantify the influence of plasticity interaction under combined primary and secondary loading. This paper reports new experiments to examine the interaction of primary and secondary loads with plasticity. These experiments were performed on three point bend specimens that had experienced a pre-compression to induce a residual stress field before being tested to failure at -150, -90 and -50 °C to correspond to varying levels of plasticity, and hence L_r, at fracture. Both 2D and 3D finite element analyses have been considered that show excelled agreement with experimental measures of the residual stress field from digital image correlation, neutron diffraction and surface hole drilling when adopting an incremental kinematic hardening model. On applying the existing R6 and the g plasticity interaction parameters to these experiments it was found that the accuracy of the methods diverged with increasing plasticity, with the g approach providing the more accurate result. However, since both the existing R6 and the g plasticity interaction parameters were shown to provide conservative results, the experiments provide useful validation for both methods.