The fracture toughness and crack propagation properties of polyester resin casts and laminates

Fracture toughness tests have been conducted on polyester resin casts and laminates containing a resin flexibilizing additive. In spite of a large change in the resin strain to failure there was little change in the critical stress intensity factor of either the resin casts or laminates. Crack growth rates for the resin casts under cyclic loading could be represented in terms of stress intensity factor range ΔK through the power law relationship da/dN=A(ΔK)^m, where A and m are constants; m was approximately 5 for all resin flexibilities. The crack growth rate was constant provided that general yielding did not occur. Fracture surfaces were examined by scanning electron microscopy, where distinct ridge structures were observed in the crack growth specimens.