Creep relaxation in the presence of residual stress

In this paper, the elastic and elastic-plastic creep behaviour of cracked structures in the presence of a residual stress field have been studied, numerically and analytically. A self-equilibrating residual stress field is introduced by prior mechanical loading. The magnitude of the residual stress field is varied and the corresponding transient crack tip parameter, C(t), is evaluated in single edge notched specimens, using the finite element (FE) method. Since the steady state crack tip parameter, C^*, and redistribution time, t_red, are no longer valid for the case of residual stress only (as for this case C^*→0 and thus t_red→∞), new normalising factors of C_norm and t_norm are introduced and used to normalise C(t) and time, respectively. Existing analytical solutions are modified based on these normalising factors, to describe creep relaxation in the presence of a residual stress field. The values of C(t) obtained from FE analysis are compared to those from the proposed equations. It has been found that the transient C(t) value provides an accurate characterisation of the crack tip fields under residual stress only.