Mesoscopic Distinct Element Method for Carbon Nanotubes: From Workstation to Massively Parallel Simulations

Abstract

Carbon nanotubes (CNT), artificially synthesized hollow cylinders with graphitic walls, have attracted significant attention as components for developing ultrastrong materials. However, scaling up the superb mechanical properties of individual CNTs to the material level poses significant challenges related mainly to the poor inter-tube load transfer between CNTs. The design of better CNT materials could benefit from guidance through numerical modeling, but neither molecular dynamics techniques nor finite element modeling could provide necessary tools for modeling the mechanics of CNT assemblies. New mesoscopic methods are needed and among coarse-grained mesoscopic models available, our mesoscopic distinct element method (mDEM) model provides premium accuracy and efficiency of bonded and non-bonded interactions as well as unprecedented length scales. This thesis is devoted to the development, enhancement, and application of the mDEM model to the modeling of CNT materials. In this work, mDEM, previously implemented in the DEM code PFC3D, is cast into an enhanced vector format and scalable parallelized with the message passing interface (MPI) technology, as enabled by waLBerla DEM multiphysics framework. The new capability allows for the modeling of large assemblies of CNTs, while distributing the computation over thousands of computational cores. With the parallelized implementation of the mDEM model in waLBerla we are able to perform unprecedented simulations, including single-walled CNT films densification and nanoindentation processing, and double-walled CNT yarns formation by stretching CNT "sock" materials. Furthermore, with a tabulation technique, mDEM is expanded to non-cylindrical collapsed CNTs. Finally, in another enhancement of mDEM model, we lay a foundation for simulation of CNT assemblies interaction with fluids.