Discrete element method for modeling solid and particulate materials.

摘要

The discrete element method (DEM) is developed in this study as a general and robust technique for unified modeling of the mechanical behavior of solid and particulate materials, including the transition from solid phase to particulate phase. When using the DEM method to model a particular problem, physical parameters governing particle interactions are usually determined by the ad hoc process of validating a numerical simulation of a standard laboratory test with an actual experimental result. However, such results are highly likely to be element size dependent. In the present approach, inter-element parameters (contact stiffnesses and failure criteria) are theoretically established as functions of element size and commonly accepted elastic constants including Young's modulus, Poisson's ratio, and fracture toughness. A main feature of such an approach is that it promises to provide convergence.; Regarding contact failure, an energy criterion based on the material's ultimate tensile strength and fracture toughness is developed to limit the maximum contact forces and inter-element relative displacement. The proposed method was then validated by modeling several test problems and results showed that indeed convergence is obtained. Moreover, a very good agreement with the theoretical results was obtained in both elastic behavior and fracture.; In this work, the proposed DEM approach is used to model penetration on concrete targets. Due to the high loading rates in such events, strain rate effects were incorporated into the proposed method. The inter-element compressive behavior was also modified to account for material densification due to compaction in the medium ahead of the projectile. Penetration, scabbing, and perforation response are characterized and compared with available empirical formulae obtained from the literature. The numerical results were found to be within the range of values for scabbing velocity (minimum velocity required to induce scabbing) and perforation velocity (minimum velocity required to completely perforate the target) given by the empirical formulae.