Effects of temperature and rate on fracture toughness of short-alumina-fibre-reinforced epoxies

The failure mechanisms of two short-alumina-fibre-reinforced epoxy resin composites (with and without rubber) have been investigated over a range of temperatures (-70°C to 100°C) and displacement rates (5 × 10^-2 mm/min to 1·8 × 10⁵ mm/min.). The fracture toughness, K_IC, of these materials is highly rate dependent but is insensitive to temperature below 50°C. Addition of alumina fibres to the epoxy matrix significantly improves the low-temperature fracture toughness. High displacement rates and low temperatures tend to promote brittle fracture with little fibre debonding and fibre pull-out. However, low displacement rates and high temperatures lead to the formation of highly non-planar fracture surfaces with extensive fibre debonding, fibre pull-out and substantial plastic shear flow of the matrix material. A qualitative model in terms of residual stresses at the fibre-matrix interface is presented to describe the temperature-dependent failure mechanisms in these composite materials.