Investigation on creep crack initiation prediction considering constraint effect using constraint parameter Q

The creep crack initiation (CCI) time considering the constraint effects induced by the crack depth of P92 steel was investigated via a two-parameter theoretical approach and computational study. Finite element method (FEM) analysis was conducted on different crack-depth compact tension specimens. It indicated that the high constraint with deep cracked depth did accelerate the damage accumulation process and reduce the creep crack initiation time. Further, the variation of the constraint parameter Q under the different crack depth was rather obtained. Moreover, the constraint parameter Q was taken into account in an analytical enhancement model, i.e. the C∗-Q approach was presented to predict the CCI time from a sharp crack tip. Finally, the comparison of the CCI between the analytical slutions and FEM results was employed to verify the accuracy of the analytical approach. It could be concluded that under K-RR-controlled field (initiation initially under the elastic stress intensity factor K-controlled field and then under the transient creep stress or Riedel-Rice (RR) controlled field condition) and HRR-RR-controlled field (initiation initially under the plastic Hutchinson-Rice-Rosengren (HRR) controlled field and then under the transient creep stress condition) could conservatively and effectively characterize the CCI time. The K-RR approach was more appropriate when initial stress intensity factor K was lower than 6 MPa m1/2, and the HRR-RR approach was more accurate when K was greater than 6 MPa m1/2.