Modelling of time-dependent hydride growth at crack tips in zirconium alloys

The steady-state velocity model of delayed hydride cracking (DHC) in hydride-forming metals developed by Dutton and Puls has been extended to non-steady-state conditions. The development of a non-steady-state DHC model is important since it makes it possible to incorporate, for the first time, a realistic hydride fracture criterion as well as to determine time-dependent hydride growth at the crack tip. To accomplish this, a computer program, PDECHEB, has been used to simulate a moving-boundary problem at the tip of a growing hydride. Mathematical models that define the moving-boundary problem have been developed and tested. Preliminary results, assuming a constant critical hydride length, show that this program gives reasonable predictions on the hydride growth behaviour and parameters such as incubation time, maximum hydride length, and DHC velocity, as a function of stress intensity factor, yield stress, hydrogen concentration in solid solution, and temperature. Since, for simplicity, the theoretically expected dependence of the critical hydride length on the above parameters was not included in this study, very close agreement with experimental results is not expected. Nevertheless, comparison with limited experimental data shows qualitatively good agreement.