Mechanical Analysis of Parameter Variations in Large-Scale Extrusion Additive Manufacturing of Thermoplastic Composites

Abstract

Large structural parts manufactured by Extrusion Additive Manufacturing (EAM) are limited by strong anisotropy due to insufficient bond formation and reduced molecular entanglement along the layer interface. To understand the correlation between process and material parameters and to enable digital modeling of EAM, the effect of different substrate temperatures and layer heights on tensile strength was investigated. A simple testing methodology for pelletized carbon fiber-filled polyamide 6 was developed. Tensile tests were performed in a full factorial Design of Experiments (DoE) to determine the tensile properties. For bulk simulation, the nominal strength and modulus were also determined based on contact width obtained by optical microscopy. The results demonstrated high anisotropy, with the maximum transverse tensile strength reaching only 27% of the corresponding longitudinal results and the transverse tensile modulus reaching only 20% of its longitudinal value. The effects of varying layer height were less significant than varying substrate temperature. The results support the hypothesis that sufficient transverse tensile strength is achieved between the extrapolated crystallization onset and melt temperature. The methodology of this study can be used as a benchmark method to qualify new thermoplastic polymers for EAM processes and to determine optimal process parameters for improved fusion bonding.