A micromechanical analysis of inter-fiber failure in long reinforced composites based on the phase field approach of fracture combined with the cohesive zone model

The nature of failure in long fiber-reinforced composites is strongly affected by damage at the microscale. The presence of different phases at different length scales leads to a significant complexity in the failure progression. At the micro-scale, the complexity is due to the presence of different points of initiation for damage and the presence of cracks propagating both in the matrix and along the fiber-matrix interfaces. This scenario gives also the opportunity to improve the material design by modifying the properties of the different constituents in order to inhibit or delay some failure mechanisms. In view of this complexity, the development of predictive numerical tools with high capabilities in terms of reliability becomes of notable importance. In order to address this aspect, the combination of the phase-field approach for fracture and the cohesive zone model is herein exploited to demonstrate its capability and accuracy for the study of failure initiation at the micro-scale. Single-fiber problems subjected to transverse loading are considered as benchmark for the prediction of the sequence of stages of failure initiation, the size effect of the fiber radius on the apparent strength, the effect of a secondary tensile transverse load and the effect of a secondary neighbouring fiber. Numerical predictions are found to be in very good agreement with experimental trends and finite fracture mechanics predictions available in the literature.