Is crack propagation in composite materials independent of fiber volume fraction?

This study used 2-D axisymmetric finite element model to simulate propagating penny-shaped crack in a brittle fiber under constant longitudinal tensile load.  The finite element analysis was divided into three separate parts.  Each part investigated the influence of a single criterion on the possibility of fiber-matrix interface failure due to the perpendicularly impinging fiber crack on the interface.  The three criteria were:  fiber-volume fraction, fiber orthotropy, and thermal load.

1. The interface tensile failure is more likely to occur when both the fiber-volume fraction and  fiber-to-matrix modulus ratio are high.

2. The interface in the silicon carbide/epoxy will not fail in shear regardless of the fiber-volume fraction.

3. In the early and middle stages of crack growth, the presence of orthotropic fiber in the graphite/epoxy composite increases the likelihood of tensile interface failure with increasing fiber-volume fraction.

4. The fiber orthotropy in the graphite/epoxy composite diminishes the likelihood of interface failure in shear.

5. The presence of thermal stress in the graphite/epoxy composite lowers the possibility of interface failure in tension and in shear.