Tensile failure due to interaction between fibre breaks

A new explanation for tensile strength of unidirectional composites is proposed based on the linking of fibre breaks in adjacent fibres if they are within a critical axial distance. No stress concentrations are included in the model. The probability of obtaining a given number of fibre breaks sufficiently close to interact is estimated by scanning an array of fibres for clusters of broken fibres. Using a simple energy balance approach it is shown that a bundle of failed fibres of a certain critical size can pull out from the rest of the composite by shear failure around the edge of the bundle, and this can be expected to lead to catastrophic fracture. Tensile strengths are obtained which are comparable with experimental data for unidirectional carbon fibre/epoxy, suggesting that it may be the interaction of fibre breaks rather than the stress concentrations associated with the breaks which is critical in determining composite tensile strength.