Simulation of intergranular stress corrosion cracking by mesh adaptivity in a cohesive zone framework

A finite element framework with mesh adaptivity was developed to simulate the oxide growth of the intergranular stress corrosion cracking (IGSCC). In particular, the environment of boiling water reactors (BWR) in combination with austenitic stainless steel and constant stress was studied. The model is interdisciplinary, it is a combination of a cohesive element fracture model, electrochemical slip-oxidation model and Fick’s second law as the diffusion model. The cyclic physics of the slip oxidation model was replicated. In the model, the thickness of the oxide was taken into consideration as the physical length of the cohesive element. The cyclic process was modelled with oxide film growth. Oxide rupture occurred due to degradation of the fracture energy. The degradation is a result of both external traction and diffusion of aggressive ions. The rate of degradation is defined by a variety of parameters as material properties, electrochemical properties and diffusivity. Next, the re-passivation will be initiated by the mesh adaptivity framework. The model was solved with a staggered solution scheme and the mesh adaptivity was set every Newton-Raphson trial. The model results agreed with experiments in the literature for changes in stress intensity factor, yield stress representing cold work and environmental factors such as conductivity and corrosion potential. The model also shows cost effective predicting, which is useful for larger simulation or optimization situations.QC 20200331