Physical Modeling: Simulation of Micro-Void Development within Large Scale Polymer Composite Deposition Beads

Short carbon fiber composites are used in large-scale polymer deposition additive manufacturing due to their increased stiffness and strength and reduced thermal expansion and print distortion. While much attention has been given to interlayer properties, less is known about bead microstructure, including the effect that suspended fibers have on porosity. This paper develops a model for single fiber motion in a purely viscous flow that is simulated with a custom finite element fiber suspension analysis. Our fiber simulation is based on Jeffrey’s model assumptions where translational and rotational velocities which zero applied forces and moments are computed. Velocity gradients along streamlines within the flow of polymer melt through a large-scale polymer deposition additive manufacturing flow field serve as input. The pressure distribution around a fiber is computed along the flow path including the die swell expansion at the nozzle exit. The simulation provides insight into micro-void formation within printed beads.