ATTRITION OF BRITTLE SPHERES BY FRACTURE UNDER COMPRESSION AND IMPACTLOADING

Results are presented of a theoretical and experimental study of the f racture of single brittle spheres by uniaxial compression between oppo sed platens and by free impact against plane targets. The stress distr ibutions in elastic spheres are broadly similar under both types of lo ading, with significant tensile components inside the sphere on the ax is of the system and on the surface of the sphere, around the equator for the case of compression. The magnitudes and locations of the peak values of these stresses depend on the size of the contact area (relat ive to the size of the sphere), which in turn depends on the mechanica l properties of the target and platen material. A simple equation used by previous investigators to estimate the maximum internal tensile st ress from the load provides a useful approximation only under certain conditions, and more generally leads to significant error. Experiments with lead glass spheres have shown that under many conditions of comp ression and impact testing, failure initiates on the surface, rather t han internally, at a critical value of tensile stress. The work is rel evant to the breakage attrition of brittle particles in powder transpo rt, handling and processing, and also to comminution. It also provides a basis for the interpretation of indirect tensile tests in which sph erical samples are uniaxially compressed.