Observation of grain size limited dynamic failure in a typical granite

Understanding the dynamic fragmentation of geological materials is important to many fields, but is particularly significant for mining. Here, a series of expanding ring experiments are reported, investigating the dynamic fragmentation of a typical granite from a mining environment. In addition to in-situ diagnostics which measure time-resolved loading characteristics, fragments were soft-captured and analysed. Measured fragment size distributions agree well with existing theory, but show unexpected strain rate variation. Specifically, the reduction in fragment size with rate is shown to be limited as the fragments neared the material grain size, a phenomenon not previously observed. Inter-granular failure was confirmed by fractographic analysis of the recovered material. The phenomenon was hypothesised to be caused by the fragmentation being dominated by an intergranular fracture mechanism which becomes inhibited when fragments near the grain size. More generally, the approach provides a new experimental route through which the fragmentation of geological materials can be understood.