Planar deposition flow modeling of fiber filled composites in large area additive manufacturing

The rapid transition of the Fused Filament Fabrication (FFF) Additive Manufacturing (AM) process from small scale prototype models to large scale polymer deposition has been driven, in part, by the addition of short carbon fibers to the polymer feedstock. The addition of short carbon fibers improves both the mechanical and thermal properties of the printed beads. The improvements to the anisotropic mechanical and thermal properties of the polymer feedstock are dependent on the spatially varying orientation of short carbon fibers which is itself a function of the velocity gradients in the flow field throughout the nozzle and in the extrudate during deposition flow. This paper presents a computational approach for simulating the deposition flow that occurs in the Large Area Additive Manufacturing (LAAM) process and the effects on the final short fiber orientation state in the deposited polymer bead and the resulting bead mechanical and thermal properties. The finite element method is used to evaluate Stokes flow for a two-dimensional planar flow field within a Strangpresse Model 19 LAAM polymer deposition nozzle. A shape optimization method is employed to compute the shape of the polymer melt flow free surface below the nozzle exit as the bead is deposited on a moving print platform. Three nozzle configurations are considered in this study. Fiber orientation tensors are calculated throughout the fluid domain using the Folgar-Tucker fiber interaction model. The effective bulk mechanical properties, specifically the longitudinal and transverse moduli, and the coefficient of thermal expansion, are also calculated for the deposited bead based on the spatially varying fiber orientation tensors. Fiber orientation is found to be highly aligned along the deposition direction of the resulting bead and the computed properties through the thickness of the bead are found to be affected by nozzle height during deposition.