Simulation for intergranular stress corrosion cracking based on a three-dimensional polycrystalline model

In stress corrosion cracking of stainless steel, two different schemes of analysis of crack growth should be employed for the crack initiation phase and crack growth phase. However, this distinction is not clear-cut in the crack initiation phase, since the vicinity of the pre-existing crack is a preferential area of crack initiation due to concentration of stress. Therefore, initiation of crack tends to occur at the tip of a pre-existing crack and it can be regarded as crack growth. In this study, the contribution of this type of apparent crack growth, referred to as initiation dominant growth (IDG), to crack growth was evaluated by a Monte Carlo simulation. A three-dimensional polycrystalline body was generated by Voronoi tessellation. The cracks were assumed to grow along grain boundaries. The effect of stress-concentration around pre-existing cracks was taken into account by applying the finite element method. Initiation and propagation of the cracks were modeled based on concepts of damage mechanics. The simulation could reproduce the changes in number of cracks and the sum of crack length obtained experimentally as well as preferential crack initiation at the stress-concentration zones and suppression of crack initiation in stress-shielding zones. It was shown that the contribution of IDG to crack growth was large for small cracks, and that damage by crack initiation accounted for more than 50% of total damage even when the length of a crack was 0.6 mm at the surface.