In this paper, the mixing process and flow behavior of different-shaped sphero-cylinders with a filling level of 40.5% in the rotating drum were numerically studied by the discrete element method. The effects of rotation speed and particle aspect ratio (AR) on the mixing and flow processes were analyzed. Various macro-and microscopic characteristics of structures during mixing were systematically investigated and their dependences on the rotation speed and AR were quantified, and the corresponding flow dynamics were illustrated. The results show that sphero-cylinders with different ARs can reach well-mixed states under sufficient rotation conditions. Both the macro-and microscopic properties change with the rotation speed and AR; however, when AR > 3, its influence becomes less obvious. The mechanism affecting the flow behavior of spherocylindrical systems lies in the fact that the interlocking restricts the movement of particles, which makes the particles detached from the drum wall at a high position, thus accelerating the transition of the flow regime.
In this study, a coupled computational fluid dynamics and discrete element method (CFD-DEM) model is constructed to deal with the motion of flexible fibers in molten thermoplastic during fused deposition modeling (FDM) 3D printing process. The effects of fiber stiffness and length on fiber bridging and nozzle clogging are investigated. Numerical results show that fiber deformation has a clear influence on nozzle clogging even when the fibers are as short as 0.24 mm for the printing of short carbon fiber reinforced polyamide-6 (sCF/PA6) composite with a fiber volume fraction of 13.34%. Through a particle-scale analysis on the fiber architecture in terms of coordinate number, contact force, and fiber orientation, the influence of fiber deformation is identified. It is found that the flexible fibers are more sensitive to the geometry and profile changes of the nozzle internal walls, which leads to a larger inclination of the flexible fiber in the nozzle. Complex interlocking structures are formed by flexible fibers in the printer nozzle, promoting the fiber bridges. The results of this paper provide insights for the development and optimization of printer nozzles to enable the printing of longer fibers without potential nozzle clogging.
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