Role of the weak interface on thoughening in layered brittle materials: a coupled phase field-cohesive zone model approach to fracture

Interfacial properties in layered microstructures such as composites, rocks, and 3D-printed brittle materials play a significant role in bulk fracture and failure mechanisms, and are critical for the purposeful design of toughening mechanisms in architected materials.Capturing the role of the interface in crack propagation of layered materials is challenging due to the need to incorporate interface elements within the bulk while accounting for bulk fracture.A coupled phase-field and CZM framework, previously developed by authors for crack impinging on an interface, was used to numerically examine the significance of including vs. excluding the weak interface for accurate prediction of crack propagation in layered and functionally graded materials.The crack penetration and deflection scenarios were examined and compared with LEFM theory for a crack tip present in the bulk.It was found that the framework accurately captures the fracture and crack-interface interaction when the crack is present in the bulk, while exclusion of the interface led to inaccurate fracture response.Interfacial failure (i.e., debonding) in the case of crack deflection provides significant energy dissipation (toughness) -17 times greater compared to penetration and 4 times greater compared to the case where the interface is excluded.These dissipative mechanisms from crack-interface interaction can help engineer tougher layered composites.A strategically engineered weak interface can effectively redirect crack propagation, transforming a catastrophic penetration failure into a more controlled deflection mechanism.