Saburo Yashima

Relationships between particle size and fracture energy or impact velocity required to fracture as estimated from single particle crushing

Abstract The relationships between fracture energy and compressive strength of sphere have been theoretically studied from the viewpoint of fracture mechanics using experimental results of crushing of spheres. Two kinds of glassy and five kinds of natural materials were examined. Specimen diameter ranged, from 0.5 to 3 cm. Combining the above with the size effect of strength reported in the previous papers, the authors obtained a new equation for the change in fracture energy with size. The specific fracture energy increased with a decrease in size and, with natural materials, when size was less than 500, μm, the specific fracture energy increased rapidly. Even if the kinetic energy of a particle with a size of 100 μm was converted completely into fracture energy, the impact velocities required to fracture were calculated to be 13 ∼ 225 m/s for the samples used in this report.

Breakage behavior of fine particles of brittle minerals and coals

Abstract Breakage behavior of fine single particles of five minerals and two coals in a size range from 88 /gmm to 1 μm was investigated by compression tests. Strength of the particles varies with particle size and their relation is similar to that of coarser particles previously given by Yashima ea . Specific fracture energy has a tendency to increase with decreasing particle size. Particles under a few micrometres deformed to a considerable extent without fracture. It may suggest even brittle materials deformed plastically. Local plastic deformation was also observed in fractured coarser particles. Critical sizes of this elastic/partially-plastic behavior and of partially-plastic/fully-plastic behavior were estimated based on theory of elasticity and microscopic observation of the particles after compression.

A consideration of grinding limit based on fracture mechanics

Abstract In general, it is well known that the energy efficiency of a grinding process decreases with decrease in produced particle size, increase in grinding time, or increase in input energy. In this paper, based on the experimental results of single particle crushing, we define the size reduction energy as the elastic strain energy which is stored in the solids up to the instant of fracture. Assuming that the kinetic energy of a grinding medium was converted completely into fracture energy, the efficiency of size reduction evaluated by the produced specific surface area has been calculated.