MEASUREMENT OF THE FRACTURE ENERGY USING 3-POINT BEND TESTS .2. INFLUENCE OF BULK ENERGY-DISSIPATION

Available measures of the fracture energy G(F) obtained with the procedure proposed by RILEM TC-50 provide values that appear to change with sample size, calling into question whether G(F) can be considered as a material parameter. In a previous paper, possible sources of energy dissipation from the testing equipment and lateral supports were considered. In this paper new possible sources of energy dissipation in the sample, apart from the fracture crack itself, are considered. Such dissipation will take place inside the bulk of the most stressed regions of the specimen and, if it is not taken into account, higher values of G(F) will be recorded than that strictly due to surface fracture energy. When this contribution and the possible energy dissipation analysed in previous work are considered, they are not enough to account for the measured size effect. If G(F) is to be considered a material parameter, the evaluation of the results from the RILEM method should be analysed more carefully. In any case, the dissipated energy reported here represents a non-negligible amount of G(F) and should be taken into account when performing measurements.