Crack propagation and compliance calibration in fibre-reinforced polymers

The critical stress intensity factor is used as a criterion for fracture since its use facilitates specification of critical defect size or critical fracture stress. It is shown experimentally that the compliance/crack length relationship for a fiber-reinforced material is significantly different to that of an elastic continuum. The difference is attributed to the different content of elastic strain energy in the composite, which is, in fact, elastically anisotropic and inhomogeneous. The experimental methods used lead to practical design against fracture in composites.