Determination of the tension softening curve of nuclear graphites using the incremental displacement collocation method

The fracture properties of two nuclear-grade graphites, the Japanese IG11 graphite and Chinese NG-CT-01 graphite, were evaluated under flexural conditions. Three-point bend tests were performed on centre-notched beams to determine the tension softening curve (TSC), Mode-I fracture toughness KIC and the fracture energy GF. The TSC of the nuclear graphites was originally determined by a newly developed incremental displacement collocation method, and was shown to be able to predict the post-peak behaviour accurately. The TSC was simplified to the bilinear, tri-linear and exponential curves. The tri-linear curve was found to be the best approximation for modelling the tension softening of these nuclear graphites. Furthermore, scanning electron microscope images of their microstructures showed that the difference in brittleness and fracture behaviour between the two graphites was probably caused by a difference in grain size and the degree of binder infiltration.