Experimental Study to Understand the Effect of Residual Stress and Applied Load on Creep Relaxation

In structural integrity analysis of components operating at high temperature, it is important to understand whether the presence of residual stresses lead to failure [1]. Accurate prediction of the creep crack initiation is needed in structural integrity assessments of components. General assessment of structures uses the experimental data obtained from laboratory test specimens subjected to either displacement or load tests but in actual operating condition, components are subjected to both inherent residual stresses and applied load. In the current research work, two test rigs are designed and tests are performed to understand the effects of EFU, long-range residual stress and external applied load on creep behaviour of 316H stainless steel. Results obtained show that, for the same total initial reference stress, the time for crack to grow is lower in the case of mixed loading conditions compared to load-controlled tests. The longer crack growth times are a consequence of the relaxation and redistribution of the residual loads in the structure. The initiation time is also a function of the elastic follow-up.