Comminution of Solids Due to Kinetic Energy of High Shear Strain Rate:Implications for Shock and Shale Fracturing

This paper outlines the basic idea of a macroscopic model on the dynamic comminution or fragmentation of rocks, concrete, metals, and ceramics. The essential idea is that the driving force of comminution under high-rate shear and compression with shear is the release of the local kinetic energy of shear strain rate. The density of this energy at strain rates >1,000/s is found to exceed the maximum possible strain energy density by orders of magnitude, making the strain energy irrelevant. It is shown that particle size is proportional to the -2/3 power of the shear strain rate and the 2/3 power of the interface fracture energy or interface shear stress, and that the comminution process is macroscopically equivalent to an apparent shear viscosity that is proportional (at constant interface friction) to the -1/3 power of this rate. A dimensionless indicator of the comminution intensity is formulated. The theory was inspired by noting that the local kinetic energy of shear strain rate plays a role analogous to the local kinetic energy of eddies in turbulent flow.