Crack propagation in metal-matrix/ metal-fibre composites: I. Strength and toughness

The strength and toughness of composites consisting of an aluminium-4% copper alloy reinforced with tungsten wires has been studied by conventional mechanical testing methods and with the aid of fracture mechanics techniques. The effects of fibre volume fraction and of the plastic deformation behaviour of the matrix alloy are shown. Values of the fracture energy, measured in a variety of ways, are compared with each other and with the predictions of existing theoretical models. One of these, modified to take account of the actual shape of the plastic zone developed during crack propagation, has been found to agree reasonably satisfactorily with the experimental results for intermediate fibre volume fractions - ie for composites in which V_f is not sufficiently high to cause splitting and not so low as to permit matrix plasticity to control the composite behaviour. The effect of the matrix work-hardening rate is found to be insignificant in composites containing more than about 12 volume% of fibres.