Simulation of Micro-Void Development within Large Scale Additively Manufactured Polymer Composite Deposition Beads

Abstract

Despite the growing level of technological advancement that characterizes extrusion-deposition additive manufacturing technology, there remains a significant knowledge gap in fully understanding the process-structure-property relationship involved in this technology. Modeling the polymer melt flow extrusion-deposition process is important in understanding the development of the inherent microstructure within the print beads, particularly the micro-voids formation and growth which significantly affects the resulting material properties and part performance. The current research presents a computational-based approach for investigating process-induced micro-voids and their impact on print properties. We develop a multiscale FEA simulation tool to predict global and local flow-fields during the polymer-melt flow process to investigate underlying mechanisms that may promote the micro-void development within the bead microstructure specifically the occurrence of low-pressure regions at sites of stress concentration such as at the tips of suspended fibers and at locations with abrupt changes in flow direction like the die-swell region just after the nozzle exit. The research also investigates potential factors that may influence the growth and development of these micro-voids such as the suspension viscosity and shear-thinning polymer melt rheology, the size and geometry of the reinforcing particles, etc. Furthermore, the research presents a method for quantifying and characterizing micro-voids within printed beads and assessing their impact on the effective material properties. The direct implication of reduced bead porosity levels is the development of high-quality functional components for specialized applications such as light weight & high strength integrity composites widely used in a variety of industries particularly the automobile, aerospace, renewable energy and defense industries.