A coupled mechano-chemical peridynamic model for pit-to-crack transition in stress-corrosion cracking

Abstract

We introduce a coupled mechano-chemical peridynamic model to describe stress corrosion cracking. In this model, two mechanisms, stress-dependent anodic dissolution and diffuse corrosion layer-assisted fracture, are considered to influence pitting and crack propagation in stress corrosion cracking. Diffusion peridynamic bonds (acting as dissolution bonds at the solid/liquid interface) and mechanical peridynamic bonds are used to represent the interactions between material points. Mechanical bonds can be damaged by mechanical stretching or by anodic dissolution. The magnitude of the dissolution fluxes for diffusion peridynamic bonds depends on both mechanical deformation and the applied electrical potential. The coupling between anodic dissolution and mechanical damage leads to cracks that initiate in the corrosion damage layer and propagate into the bulk. A 2D three-point bending/corrosion test demonstrates the concept. We verify the model in 3D using an experimental test from the literature for the case of stress-corrosion cracking process in a steam turbine steel sample. The model's results capture the pit-to-crack transition time, the pit size and shape at fracture, as well as the morphology of cracks that spring from, and connect the pits.