MICROMECHANICAL MODEL FOR COMMINUTION AND GRANULAR FLOW OF BRITTLE MATERIAL UNDER HIGH-STRAIN RATE APPLICATION TO PENETRATION OF CERAMIC TARGETS

Under sufficiently energetic attack by penetrators or explosives, brittle materials are comminuted and forced into large strain divergent flow, deforming non-elastically by sliding and ride-up of fragments, with accompanying competition between dilatancy and pore compaction. This paper describes a micromechanical model of such deformation with application to penetration of thick ceramic targets. The model was used in parametric finite element code calculations of the penetration of an eroding, long tungsten rod into a target package consisting of a thick aluminum nitride plate confined in steel. The calculations successfully exhibited the key generic features commonly observed experimentally, including the formation of a comminuted ceramic region a.round the eroding penetrator nose, dilatant expansion of comminuted material into the region behind the penetrator, and conical fractures radiating outward from this region into the intact material. The most important ceramic properties that govern the depth of penetration were inferred to be the friction between comminuted granules, the unconfined compressive strength of the intact material and the compaction strength of the comminuted material. However, further work is needed to define the relative importance of the properties of the comminuted and intact material.