The influence of size effects and dynamic loading on the fracture toughness of commercial GRP materials

The influence of specimen thickness and the effect of dynamic rates of testing on fracture toughness behaviour of laboratory-prepared and commercial glass-reinforced plastic materials have been investigated. The four materials, from different sources, gave similar fracture toughness data. The results show that the fracture toughness increases with specimen size, for specimens with nominal thicknesses in the range 10 to 25 mm; this is thought to be associated with the length of fibres in the testpiece ligament. Dynamic tests produced higher fracture toughness values than those obtained statically. This was believed to be due to a change in fracture mode from fibre fracture to fibre pull-out.