A cohesive phase-field method for seamlessly modelling intergranular and transgranular fracture in polycrystalline materials

Due to their microstructural inhomogeneity, predicting damage and fracture mechanisms in polycrystalline materials at the micron scale remains challenging. Therefore, accounting for microstructural features involved in damaging processes is of paramount importance in addressing this critical problem. This study proposes a novel cohesive phase-field approach to seamlessly simulate intergranular and transgranular failure within a realistic polycrystalline microstructure, capable of accounting for grain boundary cohesive properties. It relies on complete control of local material properties within the considered solid domain while exploiting the flexibility of the cohesive phase-field formulation. To exploit the model’s capabilities, an image segmentation technique was developed, enabling realistic microstructure modelling. This technique serves as input for Finite Element-based simulations in an open-source FEniCS library integrated into GPFniCS, a code previously proposed by the authors. Two case studies demonstrate the model’s capabilities: a one-dimensional problem with a cohesive interface and a two-dimensional cantilever bending scenario in polycrystalline material. The proposed approach is also validated with the commercial cohesive zone method (CZM). The proposed model opens new avenues for designing and optimising polycrystalline materials with unprecedented fracture toughness, while also revealing the failure mechanisms at this critical scale in currently available materials.