Analytical and numerical investigations of creep crack initiation considering the load-independent constraint parameter $${{\varvec{Q}}}^{*}$$ Q ∗

Abstract

The numerical simulation and a new theoretical approach were conducted to investigate the creep crack initiation (CCI) time and the effect of constraints induced by the specimen thickness of P92 steel. The theoretical enhanced $$C^{*}-Q^{*}$$ approach, which considered the load-independent constraint parameter $$Q^{*}$$ , was proposed to predict the CCI time around a sharp crack tip. Moreover, finite element analysis was used to verify the load independence of parameter $$Q^{*}$$ as the value of $${C}^{*}$$ varied. The larger thickness of the compact tension (CT) specimen contributed to a larger constraint parameter $$Q^{*}$$ , and the highly constrained CT specimens with larger thicknesses observably showed lower CCI times. The variation of hydrostatic stresses, triaxiality and multiaxial strain factor considering the constraint was discussed. The suitability of the analytical approach was verified to predict CCI, and the comparison between analytical and simulated results demonstrated that the $$C^{*}-Q^{*}$$ two-parameter prediction approach under stress intensity factor and Riedel–Rice (K-RR) control (initially by K, then by transient creep stress or Riedel–Rice conditions) and Hutchinson–Rice–Rosengren and Riedel–Rice (HRR-RR) control (initially by plastic HRR control, then by RR conditions) could conservatively and effectively characterize the CCI times. The K-RR solutions were more accurate when initial stress intensity factor $${K}<6\,\hbox {MPam}^{1/2}$$ , and the HRR-RR solutions were more appropriate when $${K}>6\,\hbox {MPam}^{1/2}$$ .