Grain boundary modeling issues with cohesive elements: application to intergranular stress corrosion cracking

This work highlights some of the issues regarding the application of the cohesive elements for modeling grain boundaries with the purpose of capturing intergranular stress corrosion cracking in polycrystalline aggregates. The main issue relates to the computation of the normal stresses which at the triple lines between the grain boundaries deviate from the theoretically computed values for a homogeneous, isotropic material. The issues is found in both 3D type cohesive elements in ABAQUS: COH3D6 and COH3D8. Both conformal and non-conformal meshes were investigated and the issues is observed in both. Also, the effect of different structural elements and different mesh densities was investigated. Quite small influence of both was found. The only instance where the computed normal stresses agree well with the theoretical is in the case of a very simple geometry with a conformal and completely symmetric mesh. This kind of mesh is practically impossible to obtain in the real steel structure. The applicability of the cohesive elements in this type of application is therefore questionable.