Interfacial effects in carbon-epoxies: Part 3 Toughness with short fibres

The work of fracture has been measured, using the Izod test, for short-fibre laminates. The fibres were 2 mm long and in one series of experiments were aligned, and in a second series of experiments they were random in the plane of the laminate. The work of fracture increased monotonically with increasing fibre content and fibre critical length, but values were less than expected on the basis of established fibre pull-out theory. The low values were probably due to the high resistance to debonding of these composites, since the fibre pull-out lengths at the fracture surfaces were very much smaller than the fibre critical lengths.