Automated microscopy and particle size analysis of dynamic fragmentation in natural ceramics

The dynamic fragmentation of gabbro and granitoid tiles, and coarser and finer grained granitoid blocks have been examined for impact energies of 21–6180 J. Intra-grain fragmentation and inter-granular frictional melting were observed to be common features of the fragmentation process. Consideration of analytical models indicate these temperatures are achievable under these moderate impact conditions. values of the number-based sub-10 μm fines, and the number- and volume-based 10 μm to 2 mm fragments were compared with existing theoretical models predicting dominant fragment size. The simplistic model proposed by Grady predicts reasonably well the median fragment size for the volume-based distribution. More complex models are able to predict reasonably well median values for number-based distributions. Ultra-fine production was not predictable. These results suggest there are two distinct fragment-forming mechanisms during impact testing of natural materials. One mechanism is based on energy considerations of the bulk material, which produces the larger fragment sizes, and the other is associated with micro-scale comminution, which produces sub-10 μm fines.