Single-particle crush test for ultrafine particles and direct numerical simulation of fracture process

Abstract To elucidate the crushing behavior of ultrafine particles, ultrafine monodisperse and polydisperse spherical glass particles, and irregularly shaped magnetic particles were implemented in single-particle crush tests and numerical simulations. In the case of the spherical glass particles, the obtained force–displacement curve was found to be consistent with the Hertz theory; particularly, the fracture process rapidly progressed when the breakage force was reached. In contrast, with irregularly shaped magnetic particles, the fracture process progressed gradually, with the occurrence of intermittent cracking and chipping as the load was increased. Additionally, crack initiation was found to coincide with a fluctuating load value. A comparison of the mass-specific fracture energies of the measured particles revealed that the glass particles and Sm-Fe-N magnetic particles had the highest and lowest values, respectively. This is presumably because the fracture energy is dependent on the amount and size of pre-existent cracks in the particles. Based on the breakage force results obtained in the experiment, and the particle behavior observed during the fracture process, single-particle crush tests were simulated by using an advanced discrete element method (ADEM), which enables simulation of the fracture process of particles. Although further research is required to clarify the relationship between the fracture properties and ADEM parameters, and to increase simulation accuracy, the fracture processes of 30–120-μm-diameter glass and permanent-magnet particles with a breakage force range of 150–4000 mN were analyzed by rearranging the comprising particles and altering the density and internal adhesion parameters.