Study of creep relaxation under combined mechanical and residual stresses

In this work the elastic and elastic–plastic creep behaviour of cracked structures in the presence of residual stress has been studied numerically. The residual stress is introduced by prior mechanical loading and mechanical stress levels are varied to evaluate the transient crack tip parameter, C(t), in single edge notch bend, SEN (B), and tension, SEN (T), specimens, using the finite-element (FE) method. The near tip stress distributions are examined and the influence of residual stress on the evolution of the stress fields, quantified by C(t), is examined. The values of C(t) obtained from the FE analysis are compared to existing analytical solutions. It has been found that the transient C(t) value provides an accurate characterisation of the crack tip fields under combined primary and secondary stress. It has also been found that the level of conservatism of current C(t) estimation schemes, which account for primary and secondary stress, depends on material properties and the level of primary and secondary stress.