Fracture Mechanics Analysis of the Fibre Fragmentation Test

An improved micromechanics analysis is developed for the stress transfer in the single fibre fragmentation test. Considering the partially debonded interface as the most general case, Griffith's fracture mechanics approach is employed to derive a debond criterion at the fibre-matrix interface. An average fibre strength model from the Weibull statistics is used to determine the mean fibre fragment length as a function of applied stress. A parametric study for a carbon fibre-epoxy matrix composite shows that there is a critical applied stress below which no interfacial debonding takes place. The Poisson effect increases the interface shear stress at the debonded region towards the fibre ends, which in turn discourages further debond propagation. The mean fibre fragment length is the sum of the bonded and debonded lengths, and is substantially smaller for the composite containing fibres with a higher surface treatment level at a given applied stress greater than the critical level.