Experimentally-based model for delayed hydride cracking (DHC): hydrogen diffusion, hydride nucleation, growth, dissolution and crack propagation

Delayed Hydride Cracking (DHC) is a hydrogen embrittlement phenomenon that may affect Zircaloy-4 fuel claddings. An experimental procedure was previously developed to measure the fracture toughness of this material using notched C-ring specimens with a precrack, for both in presence of DHC (KIDHC) and without (KIC) \citep{francois_assessing_2024}. Based on these experiments, and on additional experimental results on notched C-ring specimens without a precrack, a finite element model was developed to numerically reproduce the DHC phenomenon. This model couples the mechanical behavior of the material with the presence of hydrogen in solid solution and hydrides, considering the kinetics of hydrogen diffusion, and the nucleation, growth and dissolution of hydrides (HNGD model). A cohesive zone model was used for crack propagation. The numerical model successfully reproduces the experimental results and is consistent with the experimental values of KIDHC, crack propagation rate and incubation time at 150, and 200 °C for precracked specimens and 250 °C for both precracked and notched specimens. In addition, this study highlights the great influence of the swelling induced by the presence of hydrogen in solid solution and precipitated hydrides on the fracture of the material in case of DHC, and the importance to take it into account to model this phenomenon.