Analytical approaches of creep crack initiation prediction coupled with the residual stress and constraint effect

In this work, the coupled effects of residual stress and constraint on creep damage and creep crack initiation time (CCI) were analyzed by the analytical approaches based on the ductility exhaustion model. The elastic follow-up factor, Z, as well as the reference stress method and constraint parameter Q*, were considered as part of the analytical method. The variation of hydrostatic stresses, triaxiality and multiaxial strain factor considering the constraint was discussed. The suitability of the analytical method to the conditions that coupled secondary stress and the constraint effects was then investigated. Reasonable and conservative predictions of CCI time could be obtained from the theoretical solutions when the coupled effects were taken into account within the Hutchinson-Rice-Rosengren--Riedel-Rice (HRR-RR) (initiation initially under the elastic-plastic Hutchinson-Rice-Rosengren (HRR) field and then under transient creep stress conditions, the Riedel-Rice (RR) controlled stress field) and stress intensity factor-Riedel-Rice (K-RR) control (initially by K, then by transient creep stress or Riedel-Rice conditions) controlled model when compared with finite element (FE) solutions. The K-RR solutions were more accurate when primary initial stress intensity factor KPI<6 MPam1/2, and the HRR-RR solutions were more appropriate when KPI >6 MPam1/2.