STRONG BENDING IN THE DCB INTERLAMINAR TEST OF THIN, E-GLASS WOVEN-FABRIC-REINFORCED LAMINATES

The Mode I interlaminar fracture toughness of thin, woven-fabric-reinforced laminates was determined using the double cantilever beam (DCB) test. At very strong beam bending the critical crack extension force does not depend on the crack length. In this case only the critical crack extension force needs to be measured to determine fracture toughness. Measurements were also carried out by direct determination of the force arm to account for bending of the beams. Interlaminar fracture toughness (1.05-1.25 kJ m-2) of fabric-reinforced laminates is significantly higher than that of non-woven unidirectional composites. After exposure in boiling water for 6 hours fracture toughness of the laminates was not reduced. In the absence of fibre sizing agents the loss in G(lc) after exposure in water was 81%. Increasing the test temperature led to some growth of fracture toughness. Crack propagation between fabric layers was unstable, but changed to stable if the crack intersected some fabric layer.