Correlating Large-Format Additive Manufacturing Processing Parameters to Fiber Length and the Mechanical Performance of Reinforced Polymer Composites

The Big Area Additive Manufacturing (BAAM) system at Oak Ridge National Laboratory has been used to produce carbon fiber reinforced structures for several years, including vehicles, building constituents, composite tooling, etc. While the development of a large-format polymer additive manufacturing (AM) system has moved quickly, the impact of the BAAM’s extruder on the length of carbon fiber feedstock has not been systematically studied. Numerous studies in processing fiber reinforced thermoplastics in plasticizing and injection molding systems have shown that fibers are subjected to significant shear as they are processed, which can cause a drastic reduction in fiber length which negatively affects tensile strength. Recent efforts to improve mechanical properties have focused on interfacial properties and addressing meso-structural defects, so this leaves significant opportunities to improve mechanical properties of printed structures by understanding the degree of fiber length degradation in processing. Understanding the relationship between fiber degradation, processing speed, and tensile properties, will give users of any large-scale, screw-extrusion AM system a powerful tool to better tailor the mechanical properties of their parts to the application.