On the mitigation of the fiber breakage in material extrusion based additive manufacturing of carbon fiber reinforced polymer composites

A coupled computational fluid dynamics and discrete element method (CFD-DEM) model has been developed to characterize multiphase flow interactions between non-Newtonian fluid and flexible fiber in material extrusion additive manufacturing (MEX AM). The breakage mechanisms of carbon fibers in conventional MEX AM process are revealed through systematic investigation of the multiphase flow dynamics between carbon fibers and molten polymer during extrusion deposition. The results demonstrate that the stable fiber structure with high contact density arising from constraints of boundary wall and confined space serves as a critical factor inducing substantial mechanical forces that leads to fiber deformation or even breakage. Two optimization cases for the deposition of long carbon fiber reinforced composites have been developed, i.e., enlarging raster height and adjusting nozzle feeding angles (NFA) to mitigate substantial mechanical forces on fibers. The optimization efficacy has also been quantitatively evaluated through critical performance parameters including fiber deformation magnitude, fiber breakage content and fiber orientation distribution. It is found that adjusting NFA yield excellent performance in concomitantly mitigating fiber breakage while improving the fiber orientation. Finally, experimental observations confirm the effectiveness of the adjusting NFA. This study establishes numerical framework for the development and optimization of MEX AM systems for printing long discontinuous carbon fiber reinforced polymer composites, providing insights for mitigating fiber breakage while maintaining uniformity of the fiber orientation.