Measurement and modelling of crack propagation velocity in a viscoelastic matrix composite

The steady-state propagation of a crack in a continuous carbon-fibre/epoxy-matrix composite was produced in a tapered double cantilever beam specimen subjected to a constant-velocity opening. Tests were performed at room temperature. Constant crack speed, driving force and stress intensity factor during crack extension were measured for each crosshead velocity. Viscoelastic creep functions of the material were also determined. Schapery's model of viscoelastic fracture was shown to describe the slow crack propagation phenomenon adequately, provided the dependence of fracture energy on crack velocity was taken into account.