Experimental assessment of continuum breakage models accounting for mechanical interactions at particle contacts

Particle size and shape are major factors in determining the mechanical behavior of granular media. This paper discusses experiments conducted at particle and assembly scales on two materials (i.e., glass beads and quartz sand) and it interprets them in light of fracture mechanics theories. First, diametral compression tests on particles of varying size have been conducted to measure the energy stored in individual grains at the onset of fracture. Then, oedometric compression tests on samples made of the same particles have been performed to measure the yielding pressure, as well as to track the evolution of breakage. These experiments have been used to test the performance of recently proposed scaling laws bridging the energy released by a single particle with the work input required to comminute an assembly. The results show that the variables associated with macroscopic comminution scale with the grain size according to the same power law functions that control the size-dependence of the corresponding particle-scale quantities. Major differences between the scaling laws of glass beads and quartz sands have been found, with the former approaching the size effect law associated with fracture by central splitting and the latter being closer to the trends predicted by fracture at the contacts. These findings emphasize the key role of the particle shape on the energetics of breakage, thus motivating further studies focusing on different shapes, for which even wider ranges of fracture modes and scaling laws may exist.