Browsing by Subject "fiber orientation"

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Effect of Extrudate Swell, Nozzle Shape, and Convergence Zone on Fiber Orientation in Fused Deposition Modeling Nozzle Flow
(University of Texas at Austin, 2015) Heller, B.P.; Smith, D.E.; Jack, D.A.
Recent advances for improving the mechanical properties of materials used in Fused Deposition Modeling (FDM) include the addition of carbon fibers to the filament feedstock. During processing, the flow field within the polymer melt orients the fiber suspension, which is important to quantify since fiber orientation influences mechanical and thermal properties. This paper presents a computational approach for evaluating polymer melt flow and fiber orientation within a FDM nozzle taking into consideration the converging flow in the nozzle, fluid expansion caused by extrudate swell, and nozzle exit shape. Finite elements are used to evaluate the Stoke’s flow in an axisymmetric nozzle and fiber orientation tensors are evaluated along streamlines within the flow using the Fast Exact Closure and Folgar-Tucker isotropic rotary diffusion. Fiber orientation is shown to increase in the shear-dominated flow through the nozzle, however, alignment is found to decrease in the expansion flow of the die swell.
The Effect of Polymer Melt Rheology on Predicted Die Swell and Fiber Orientation in Fused Filament Fabrication Nozzle Flow
(University of Texas at Austin, 2017) Wang, Z.; Smith, D.E.
Short carbon fibers suspended in the polymer feedstock enhances the mechanical performance of products produced with Fused Filament Fabrication (FFF). As the melted filament is extruded and deposited on a moving platform, the velocity gradients within the polymer melt flow orientate the fibers, and the final orientation has a direct effect on the mechanical properties of printed bead. This paper numerically simulates an FFF nozzle flow, including the extrudate material beyond the nozzle exit. Finite element simulations of the extrusion process are performed with Generalized Newtonian Fluid (GNF) models and a viscoelastic rheology model, included in ANSYS Polyflow, to evaluate the polymer melt velocity field and predict die swell. Fiber orientation tensors are computed along streamlines using the Fast Exact Closure and Folgar-Tucker isotropic rotary diffusion. The predictions indicate that shear thinning behavior reduces the die swell but viscoelastic rheology significantly intensifies the extrudate swell. Orientation tensor values calculated from the flow results of the viscoelastic model yields lower principal alignment in printed beads than those computed with GNF models.
Next-Generation Fibre-Reinforced Lightweight Structures for Additive Manufacturing
(University of Texas at Austin, 2018) Plocher, J.; Panesar, A.
In an attempt to realise next-generation lightweight parts and to fully utilize the inherent design freedom of AM, we propose a topology optimization based design procedure that includes the anisotropic considerations for continuous fibre printing of variable stiffness composites. In this paper, we aim to improve the normalized compliance of a beam in a three-point bending scenario, using a skeletal reinforcement for a topology in which the change in fibre orientation is derived from the medial axis information. FDM with a dual-nozzle system printing nylon and carbon fibre filaments were utilized for fabrication. The toolpath i.e. reinforcement strategy available from the commercial software Eiger® was chosen to imitate the proposed strategy. The numerical investigation is complemented with experimental tests and a general benchmarking is conducted using standard pedants. The results have shown improved specific flexural stiffness for samples with skeletal reinforcement. The skeletal information is therefore considered as important tool for the retrieval of fibre angles which align with the principle stresses and therefore allow for a more efficient fibre placement in AM parts for future lightweight end-use parts.
Screw Swirling Effects on Fiber Orientation Distribution in Large-Scale Polymer Composite Additive Manufacturing
(University of Texas at Austin, 2018) Wang, Zhaogui; Smith, Douglas E.
Large-Scale Additive Manufacturing (LSAM) polymer deposition employs a single screw extruder to melt and deliver the pelletized feedstock resulting in significantly higher flow rates as compared to conventional filament-extrusion AM processes. Single screw swirling motion in the melt flow during processing generates a unique pattern of flow-induced fiber alignment when fiber-filled polymer feedstock is processed. This paper investigates the effect of the single screw swirling motion on the fiber orientation and predicted elastic properties of a printed extrudate. A finite element extruder nozzle flow is created, where the extruder screw tip, the extrusion nozzle, and a short section of free extrudate compose the melt flow domain. The IRD-RSC fiber orientation diffusion model is applied to capture the slow orientation kinetics of short fibers in the concentrated fiber suspension. The results indicate that the swirling motion of the flow has a direct effect on predicted fiber orientation distribution and the associated averaged elastic properties in the extruded composite bead.
Simulation of Mutually Dependent Polymer Flow and Fiber Filled in Polymer Composite Deposition Additive Manufacturing
(University of Texas at Austin, 2019) Wang, Z.; Smith, D.E.
Short fiber-filled polymers experience increasing applications in melt extrusion additive manufacturing. As the filled polymer is melted and extruded, the fiber-filled polymer suspension exhibits mutually dependent effects, such that flow kinematics influence fiber orientation while the fiber alignment affects the formation of melt flow. This paper presents a fully-coupled numerical scheme to characterize the mutually dependent effects between melt flow and fiber orientation in a non-Newtonian axisymmetric extrusion flow including a free surface using the Galerkin Finite Element Method. The power law fluid model is employed to characterize the shear thinning rheological behaviors of polymer melts. This approach is used to solve the fully-coupled flow velocity and the fiber orientation fields for the nozzle extrusion flow in a large-scale polymer deposition additive manufacturing process. Computed results obtained from both the weakly-coupled and fully-coupled schemes exhibit notable differences in the flow velocity, fiber orientation tensor fields, die swell of free extrudate, and predicted elastic constants.
Simulation of Planar Deposition Polymer Melt Flow and Fiber Orientation in Fused Filament Fabrication
(University of Texas at Austin, 2017) Heller, B.P.; Smith, D.E.; Jack, D.A.
Mechanical and thermal properties of a 3D printed part are improved by adding discrete carbon fibers to the Fused Filament Fabrication (FFF) polymer feedstock. The properties of the fiber-filled composite are significantly influenced by the orientation of the carbon fibers within the extruded bead where fiber orientation in the bead is affected by the nozzle internal flow geometry, extrudate swell, and the deposition flow during the FFF process. In this work, a 2D Stokes flow finite element analysis is performed to evaluate FFF extrusion for a large-scale deposition extruder where special attention is given to the deposition of polymer melt on the moving platform below the nozzle. The shape of the extruded polymer is computed using a free surface normal velocity minimization technique. Once the velocity field and flow boundary is computed for the bead deposition process, fiber orientation and the resulting mechanical properties of the solidified composite are computed within the printed bead.