An anisotropic cohesive phase field model for quasi-brittle fractures in thin fibre-reinforced composites

Thin unidirectional-tape and woven-fabric composites are widely utilized in the aerospace and automotive industries due to their enhanced fatigue life and damage resistance. Providing high-fidelity simulations of intra-laminar damage in such laminates is a challenging task both from a physics and a computational standpoint, due to their complex and largely quasi-brittle fracture response. This is manifested by matrix cracking and fibre breakage, which result in a sudden loss of strength with minimum crack openings; subsequent fibre pull-outs result in a further, although gradual, strength loss. To effectively model this response, it is necessary to account for the cohesive forces evolving within the fracture process zone. Furthermore, the interaction of the failure mechanisms pertinent to both the fibres and the matrix necessitate the definition of anisotropic damage models. We propose a cohesive phase-field model to simulate intra-laminar fracture in fibre reinforced composites. To capture damage anisotropy, distinct energetic crack driving forces are defined for each pertinent composite damage mode together with a structural tensor that accounts for material orientation dependent fracture properties. The material degradation is governed by a 3-parameter quasi-quadratic degradation function, which can be calibrated to experimentally derived strain softening curves. The proposed damage model is implemented in Abaqus and is validated against experimental results.