Characterizing internal porosity of 3d-printed fiber reinforced materials

As the functional requirements for 3D printed parts become more demanding, the use of fiber reinforced materials in material extrusion printers is increasingly common. Although fiberreinforced thermoplastics offer higher stiffness and strength, the internal volume of the extruded material often has a high degree of porosity which can negatively impact mechanical properties. This research surveys the internal porosity present across a range of material extrusion additive manufacturing platforms, primarily those involving a single screw extruder, such as the Big Area Additive Manufacturing (BAAM) system. The porosity within the volume of an extruded bead was quantified through image analysis of cross sectional micrographs. The impact of extrusion rate, transient vs steady state flow, multiple hardware configurations, and material conditions were evaluated. Across the five systems studied porosities ranged from 0.1% to 18.4% with the greatest reductions in porosity coming from two systems that added a vent to the extruder barrel which lowered porosity 64% in one case and 98% in the other.