During the third year of this project we focused on the following activities:
• We have completed the study of the force displacement law for high densities which was also part of a parallel leveraging project funded by Abbvie. This work has demonstrated that the utilization of DEM to high relative density compaction problems requires a completely different approach to the force displacement law than traditional DEM. The contact response between particle was found to depend on the overall triaxiality of the contact deformations on of the particle. A new deformation fabric tensor was proposed based on the deformation and direction of all contacts on a particle. These results form the basis for more appropriate force-displacement laws at contacts that can be implemented in discrete element simulations for high density problems.
• A detailed study was conducted on the contact problem between dissimilar spheres (different radii and different materials cases). This problem is central in the cases of powder mixture compaction. New results are presented in the report.
• An experimental study was conducted in the NaCl-Starch system – a binary system with peculiar behavior in terms of the strength of mixtures. We have first repeated the experimental results to verify them. We have identified a different method of milling that produces completely opposite trends. Our analysis of results indicates that there is a strong coupling between the milling process and the microstructure of the compacts. The milling process results in essentially a change of the particle size that depends on the materials of the mixture.
Ongoing work focuses on (a) the introduction of failure models in DEM, (b) the extension of the large relative density approach for DEM for multi material systems, (c) understanding the role of shear motions in multi material systems, (d) parametric studies for powder mixtures (d) model validation.