Computational modeling of fiber reinforced composites melt flow in nozzle extrudate for polymer deposition additive manufacturing.
Understanding effects of processing conditions on properties of processed composite materials for polymer deposition additive manufacturing is critical, especially in the recent-emerging Large Area Additive Manufacturing (LAAM) polymer composite deposition technology. This dissertation aims to broaden the knowledge of how manufacturing inputs affect LAAM bead output properties (e.g., extrudate swell, fiber orientation, and effective elastic constants). The finite element method is applied to solve the flow kinematics and free surface shape of the nozzle-extrudate polymer melt that is defined by generalized Newtonian and viscoelastic flow models. The Folgar-Tucker Isotropic Rotary Diffusion (IRD) model and the Reduced Strain Closure (RSC) model are employed to compute the Advani-Tucker second order fiber orientation tensors throughout the flow domain of interest. The one-way weakly coupled and two-way fully coupled analyses of flow and fiber orientation in the nozzle-extrudate flow domain are both implemented separately. The computed results, based on typical LAAM nozzle flow conditions, show that the non-Newtonian viscoelastic rheology effect significantly increases the die swell ratio of the Acrylonitrile Butadiene Styrene (ABS) melt by 50% as compared to the result predicted by using the Newtonian model. The swirling-flow-predicted fiber orientation tensor results yields a 25% increase in the predicted flow-direction elastic modulus of a 13% carbon fiber filled ABS (CF-ABS) as compared to that of a non-swirling simulation. It is also found that the bias of ignoring the screw-extrusion-resulted fiber length distribution in the prediction of elastic properties can be as large as 12%. Numerically predicted elastic properties from above studies exhibit a favorable agreement with related experimental measurements in the literature on similar materials and LAAM systems, which supports our proposed computational methodologies. Above results are obtained based on the weakly coupled formulation. Finally, it is found that the fully coupled interactions between the polymer melt flow and the fiber orientation has a pronounced impact on the nozzle-extrudate flow domain where the die swell of the free extrudate of 20% CF-Polyethylenimine reduces by a factor of ~2x as compared to the result of the neat polymer alternative. This agrees well with data appearing in prior experimental studies on similar filled-polymers.