On the compaction of granular media using a multi-particle finite element model

A Multi-Particle Finite Element Model (MPFEM) has been developed and was used to explore the compaction of granular media. Individual particles discretized with a finite element mesh allow for a full description of the contact mechanics and the local and global particle kinematics. Compaction modes ranging from hydrostatic to that of high shear are studied at various levels of interparticle friction to understand all stages of the powder compaction process.; Isodensity curves in hydrostatic/deviatoric stress-space during densification are shown to take the equivalent shape of a cap and cone model. Such a mechanical response predicted by this model is softer than the one predicted by other models resulting from simplifications on interparticle contact behavior. The micromechanical behavior has also been studied with the MPFEM with focus on rearrangement and translational and rotational motion which are significantly affected by both interparticle friction and macroscopic stress triaxiality. Local deviatoric stresses and equivalent plastic strains are present during the formation of stress chains at low relative densities indicating that contact deformation can occur early in densification.; Unloading of compacts was explored with MPFEM. The importance of interparticle cohesion was clearly demonstrated at the very last stages of unloading which was verified with experiments. Such analysis could aid in the diagnosis of problems with compact performance before ejection.; Probing yield surfaces that describe comprehensively the overall material behavior of compacts were generated with the MPFEM. Analytical and computational discrepancies in the probing yield surfaces are a matter of the assumptions made regarding the particle constitutive behavior and more importantly the particle kinematics. With the MPFEM model, a 'softer' yield surface is obtained as compared with other modelling efforts. Differences seen between the strain paths are verified but are less extreme as those proposed by approximate analytical models and the DEM models. The results of MPFEM are in line with the recent experimental work of S. Galen (Drexel PhD 2004).; This work illustrates that the MPFEM model is useful in describing the interparticle behavior and its effect on microscopic and macroscopic response for various strain histories at all stages of the powder compaction operation.