The general objective of the work at Surrey has been to elucidate the mechanisms of particle breakage under impact and sliding conditions. Predictive models, describing the chipping under impact and sliding conditions, have been developed based on indentation fracture mechanics. The specific objectives of the current work are to investigate the mechanism of particle fragmentation under impact and to characterise the mechanical properties of porous materials.
The study of fragmentation involved single particle impact tests in a range of impact velocities and feed particle sizes. The test materials covered a wide range of diverse mechanical properties and structures. The effect of impact velocity and feed particle size on breakage was evaluated using the full size distribution of the impact product. The analysis of the experimental results was by recourse to the Gates-Gaudin-Schumann distribution. The cumulative size distribution of the complement, i.e. the size range where fine debris and fragments arc expected, is shown to be a function of the group U’l . This conclusion is qualitatively similar to that applying to the chipping of particulate solids.
In an effort to incorporate the influence of material properties on the extent of fragmentation, the fracture toughness of spherical porous silica particles was measured using quasi-static Vickers indentation. The values of fracture toughness were found to be independent of the applied load and to fit well the expressions proposed in the literature. Fracture toughness is the most appropriate parameter for the characterisation of the resistance of materials to breakage, and the current work aims at establishing a relationship between porosity and fracture toughness by carrying out measurements on a single test material at different levels of porosity. The mechanical characterisation is expected to provide valuable information in the analysis of the effect of material properties on the fragmentation of particulate solids.