MODELING OF TIME-DEPENDENT HYDRIDE GROWTH AT CRACK TIPS IN ZIRCONIUM ALLOYS

The steady-state velocity model of delayed hydride cracking (DHC) in h ydride-forming metals developed by Dutton and Puls has been extended t o non-steady-state conditions. The development of a non-steady-state D HC model is important since it makes it possible to incorporate, for t he first time, a realistic hydride fracture criterion as well as to de termine 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, sh ow that this program gives reasonable predictions on the hydride growt h behaviour and parameters such as incubation time, maximum hydride le ngth, and DHC velocity, as a function of stress intensity factor, yiel d stress, hydrogen concentration in solid solution, and temperature. S ince, for simplicity, the theoretically expected dependence of the cri tical 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 qualita tively good agreement.