Four point bending end notched exure (4ENF) tests were used to evaluate the mode II fracture toughness
(G
IIC
) of glass bre reinforced vinyl-ester (GFRP) specimens in order to expose the sensitivity of G
IIC
to
loading rate. Tests were carried out at load displacement rates ranging from 1 to 6000 mm/minute. 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, G
IIC
tended to increase as loading rate was increased.