Axial strength inaccuracy

It is important to keep in mind that the treatments applied are gross simplifications of reality and are only applicable to brittle composites, e.g. thermosetting polymers and ceramics. In reality, for brittle materials, the load is never entirely transferred to the matrix or to the fibre due to load transfer across interfaces even after fibre or matrix failure. The fibre strength, sfu, is also not a constant for a given type of fibre; instead there is a range of strengths, described by Weibull statistics, due to varying flaw sizes (fracture obeys the Griffith criterion). Another effect not accounted for is the redistribution of stress associated with the fracture of each fibre segments.

Several models have been proposed to treat this process, essentially falling into two groups: “cumulative weakening models” and “fibre break propagation models”.

These are not covered in this TLP (see Hull and Clyne, 1996).