Influence of loading rate on the mode II fracture toughness of vinyl ester GRP

Four point bending end notched flexure (4ENF) tests were used to evaluate the mode II fracture toughness (GIIC) of glass fibre reinforced vinyl-ester (GFRP) specimens in order to expose the sensitivity of GIIC to loading rate. Tests were carried out at load displacement rates ranging from 1 to 6000 mm/min. Finite element models were used to evaluate the correction factors that are required during data reduction in order to compensate for geometrical non-linearity in the test. A high speed video camera was used in conjunction with the digital image correlation technique to measure crack propagation during the tests. It was found that, for short crack lengths, GIIC tended to increase as loading rate was increased.