Modeling the comminution and flow of granular brittle material

Abstract

Penetration weapons or explosive charges in brittle materials (such as ceramics or hard rock) cause fracture and fragmentation near the cavity boundary to produce a bed of fragmented or granulated material. Subsequent large shear deformation and flow of the granulated material occur under confining pressures that range from many GPa to zero. Under these conditions the granulated material exhibits both dilatancy and compaction. In addition, the granules undergo further comminution with a resultant reduction in average granule size, and often with localization into a layer of very fine fragments next to the cavity wall. This paper presents an update of a previously-reported mesomechanical model of these processes that is based on an analogy with atomic dislocation theory [1,2]. That is, the model focuses on a description of the flux of lines of spaces (dislocations) between granules across the boundaries of a relevant volume element (RVE) rather than on the granules themselves, and on the nucleation of new dislocations inside the control volume by comminution of granules. Outward dislocation flux from the RVE causes compaction whereas inward flux causes dilatancy. The model is cast in the form of a multiplane plasticity model in which granule sliding on interfaces is restricted to a finite number of planar surfaces with specified initial orientations. The planes are allowed to rotate during deformation. The model is designed for use in finite element computer codes, and correlations are shown with long rod penetration experiments. A parameter sensitivity study reveals that the penetration behavior is strongly dependent on initial porosity, coefficient of friction between sliding granules, and on details of the granule comminution profess.