The mechanical testing of nuclear graphite

Two billets of nuclear grade medium-grained semi-isotropic graphite were machined into rectangular 4-point bend and L-shaped specimens and tested to failure. The material was not irradiated. During the testing, as well as determining the failure load, the failure was monitored by a high speed camera. The results showed that: there was a difference in the failure loads both along a billet and between the billets, in the L-shaped specimens the cracks did not fail instantaneously but needed further movement of the testing machine’s crosshead before total failure, and the speed of the crack varied in the different specimens. The data were analysed and it was found that the Weibull theory does not predict the failure well but fracture mechanics does provide a way of correlating the data, particularly the crack propagation.