Effect of mixed mode loading on the crack propagation direction in hydrogen assisted cracking

Abstract

The four-point bending tests were carried out in deionized water on the precracked specimens of high strength Ni-Cr-Mo steel, and the crack initiation time as well as the crack propagation direction in hydrogen assisted cracking (HAC) under mixed mode I–II loading were investigated. The crack propagation angle θ p , under mixed mode I–II loading increased with increase in the ratio of mode II to mode I stress intensity factor, K II/K I , both in HAC and unstable fracture in air, and the θ p was a little larger in HAC than in unstable fracture in air. Crack initiation time in HAC, t 1 , increased with increasing K II/K I , when K II/K I , was smaller than 0.8. The above experimental results were able to be explained by denning a hydrogen-assisted cracking function g̃s (r, θ) which was introduced by combining the tangential stress σ θ , and the hydrogen concentration around crack tip.