Analysis of Fiber Attrition and Mechanical Performance in Large-Format Additive Manufacturing of Long-Fiber Reinforced Polymer Composites

Understanding the residual fiber length of discontinuous fiber-reinforced thermoplastics in large-format additive manufacturing (LFAM) is of significant interest since the residual fiber length influences the mechanical properties of the final part. Currently, the attrition of long fiber reinforcement during screw-extrusion LFAM is an understudied subject, although the residual fiber length is among the most important microstructural properties of fiber-reinforced composites. A contributing factor the lack of focus in this area is the questionability and variety of convoluted fiber measurement methods. This study evaluates the relationship between printing speed, the final fiber length, and resultant mechanical properties for 4 mm pultruded thermoplastic polyurethane (TPU) pelletized feedstock and seeks to fully document a fiber length distribution (FLD) measurement method. Samples were printed at several processing speeds and subjected to fiber length analysis and tensile testing. Fiber length analysis was performed using a combination of novel and proven techniques for improved repeatability and reliability of results. This study seeks to improve understanding in the choice of machine design, material selection, and processing parameters for optimal mechanical properties.Mechanical Engineerin