Crack tip opening displacement based description of three-dimensional creep crack border stress fields for partially penetrating cracked specimens

Abstract

The most important ability of fracture mechanics is how to apply the material test data obtained by standard specimens with the through-thickness cracks to practical structures where partially penetrating crack growth usually spends most of the service life, but complicated stress states make it difficult to describe the creep crack border stress states effectively. Based on the creep stress intensity factor Kδ(t)-Tz, a crack tip opening displacement based description is proposed to characterize the creep crack border fields for partially penetrating cracked specimens under out-of-plane constraints described by Tz. Comprehensive three-dimensional finite element results show that in the whole range of elliptical parametrical angle and shape factor, the maximum change in Kδ(t)-Tz is within 19% while C(t) changes over 370%, showing that Kδ(t)-Tz is more stable than C(t). At both primary and steady creep stages, the Kδ(t)-Tz description can characterize the crack border stress fields effectively for specimens with surface and corner elliptic cracks. Consideration of the in-plane constraint coefficient Q* is found to be necessary only for embedded elliptic cracked specimens, where the Kδ(t)-Tz-Q* description can provide an accurate prediction of crack border stress fields. The dominance and stability of Kδ(t)-Tz and Tz make the crack tip opening displacement based description potentially to develop creep fracture assessment approaches for high temperature structures.