Numerical analysis of multi-field coupling behaviors of delayed hydride cracking for thin plate-type Zr-2.5Nb specimens

Zirconium alloys are extensively utilized as structural materials in nuclear applications due to their exceptional mechanical strength, corrosion resistance, and low thermal neutron absorption cross-section. The stress concentration provoked by the defects in zirconium alloy components will initiate delayed hydride cracking (DHC), significantly jeopardizing nuclear safety. In the present investigation, an enhanced cohesive model that incorporates the effects of stress state has been proposed to realize the three-dimensional simulation of multi-field coupled DHC behaviors in thin plate-type zirconium alloy specimens. The simulation results indicate that: (1) the consistence of the predicted DHC velocities with the corresponding experimental data validates the newly developed cohesive model; (2) the strip characteristics presented in the cracked surface are captured, demonstrating that the varying fracture patterns across the thickness are well simulated; (3) the stress-state induced hydrostatic-stress gradients and solid-soluted hydrogen concentration gradients make against the formation of a hydride strip to induce hydride embrittlement near the plate surfaces, resulting in a slower cracking of the surface layers than that of the internal region; for the thinner specimens the asynchronous cracking phenomena through the thickness will greatly affect the multi-field coupling behaviors around the mid-plane; the non-cracked surface layers will apply the dragging effects to the new cracking of the internal region, leading to longer waiting time and thicker hydrided zone before fracture.