Study of the stress induced granular consolidation process by 3D DEM simulation

Abstract

Today’s powder processing technology requires a satisfactory explanation for the evolution of internal structure of powder compacts during the entire consolidation process. Many industries, where processing problems occur, can make use of such an explanation for the process development as well as for their problem solving techniques. Pharmaceutical industry, which tackles with “capping” phenomenon, and, metal and ceramic industries that deal with “near-net shape forming” problems are amongst a few examples of such industries. Many experimental and theoretical studies based on continuum mechanics have been carried out to study the macroscopic mechanical responses of compacts [1]. In recent years, the finite element method has also been adopted in simulations of powder compaction [2]. However in continuum models, the microscopic properties that strongly influence the macroscopic behavior cannot be taken account of. To get optimal mechanical properties of green compacts, better knowledge of the relation between powder characteristics and mechanical behavior of the material during compaction is required. The Discrete Element Method, developed by Cundall and Strack [3], is an effective numerical tool to investigate the micro mechanics of granular materials. In DEM, each individual particle of an assembly is modeled separately and its motion is defined from the interactions with neighboring particles. Then microscopic evolution of the internal stress and the structure of the assembly can be obtained. In the mean time, the macro behavior of the whole assembly can be obtained by statistical sum and average the properties of individual particles. In this paper, a discrete element model, which is capable of modeling friction, cohesion and local plastic deformation at the inter-particle contacts, is used to simulate quasi-static uniaxial compaction of particle assembly. The evolution of microscopic properties of the particle assembly, are presented correlated with the bulk behaviors of the compacts. The relations between particle properties in micro level and macroscopic mechanical properties of the compacts are demonstrated by the comparisons of the numerical results. These results may be further incorporated to an appropriate continuum constitutive model, and used to generate the material parameters of the powder compacts which are sometime very difficult to measure in the experiments.