Damage accumulation at notches and the fracture stress of carbon-fibre/polymer composites: Combined effects of stress and temperature

Damage accumulation around a notch in a tough thermoplastic or a toughened thermosetting polymer containing carbon fibres has been shown to depend on the magnitude of the localised tensile stress, temperature, extent of thermal cycling and ductility of the matrix. The nature and extent of damage have been investigated by X-ray radiography. Thermal cycling to moderate temperature sets up thermal stresses and expansion effects whilst high-temperature cycling is responsible for the development of microcracks. Tensile tests in monotonic and cyclic loading of coupons containing a circular hole have been carried out over a range of temperature up to the melting point or degradation of the polymer. Whilst raising temperature reduces the notch sensitivity of the laminate by blunting effects e.g. increasing split length at the notch tip, a weakening effect of the unnotched material at the notch tip dominates and the fracture stress falls. (C) 1997 Elsevier Science Limited.