Energy of fracture for short brittle fiber-brittle matrix composites with planar fiber orientation

The addition of brittle fibers to a brittle matrix can increase the toughness of the matrix providing mechanisms for energy dissipation during crack propagation. A model based on probabilistic principles is developed to calculate the increased energy absorption during fracture for a brittle matrix reinforced with very short, poorly bonded fibers. The proposed model may be used with any planar orientation distribution which can be probabilistically described. A physically plausible fiber critical angle beyond which fibers fracture by bending stresses rather than pull-out is incorporated in the model. The fiber pull-out energy is assumed to dominate other fracture energy terms, and simple parametric studies are given to demonstrate the effect of fiber orientation, fiber length, fiber diameter and fiber-matrix interfacial shear stress. The model predictions compare satisfactorily with the limited data available and offer a conceptual framework for considering the effect of changing the physical variables on the fracture energy of the composite.