Fracture characteristics of discontinuous carbon fibre-reinforced PPS and PES-C composites

Tensile strength, σ_b, Young's modulus, E, and critical stress intensity factor, K_IC, of two types of short carbon fibre (CF) reinforced high performance brittle thermoplastics (CF/PPS and CF/PES-C) have been measured for different volume fraction, V_f, of CF. Young's modulus increases linearly with increasing of V_f with a Krenchel's efficiency factor of 0.05, whereas σ_b and K_1C initially rise and then level up at V_f of 25 vol. %. With the help of load-deflection curves and fractography, the experimental results have been analyzed in the light of fibre-matrix adhesion characteristics. By using crack pinning model, the effective crack tensions, T, were calculated for both composites and they are 26 KJ/m (for CF/PPS) and 2.1 KJ/m (for CF/PES-C) respectively. The localized plastic deformation near fibre-matrix interface provides the major contribution to fracture toughness.