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.
This study used a Discrete Element Method (DEM) model to investigate the
Jenike shear process of flexible, cylindrical particles with different
aspect ratios. The model was validated through experiments and
analytical solutions. It was found that particle shape and deformation
have a significant impact on friction behavior, affecting particle
deformation, contact forces, orientation, and internal friction angle.
Results indicate an increase in shear stress with normal load,
regardless of particle stiffness or shape. Flexible particles showed
higher shear stress and internal friction angles than rigid ones,
especially for aspect ratios of 6. With aspect ratios of 4 and 5,
flexible particles deform significantly during shear with complex
reconfiguration, while aspect ratio 6 particles experience a uniform
reconfiguration, indicating a solid packing structure that enhances flow
resistance. These findings will aid in improving kinetic theories for
granular flow of complex irregular particle flows.
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