Effects of High Temperature Compaction on 3D Printed Carbon Fiber Reinforced Polymer Composites

The aim of this dissertation was to study the effects of hot temperature compaction (HTC) upon the polymorphism and the mechanical behavior of an additively manufactured (AM), carbon fiber reinforced polyamide (PA6). Different pressure and temperature levels during HTC were tested to determine the overall effect upon the mechanical behavior and the material crystalline composition. Treated, carbon fiber reinforced PA6 samples were analyzed using differential scanning calorimetry, x-ray diffraction, thermogravimetric analysis, scanning electron microscopy, double cantilever beam testing and three-point bending testing. When considered with respect to as-printed samples, an HTC temperature of 190°C combined with 80 psi pressure resulted in increased flexural modulus and flexural strength by 47% and 58%, respectively. This increase was attributed to the decrease of AM induced cracking, voids (both inside and between the beads), and a crystalline solid-state transition in the PA6. However, compaction also leads to embrittlement as the level of crystallinity increases. A double cantilever beam characterization demonstrated that this increase in crystallinity served to reduce the fracture toughness of the material. Therefore, HTC can help overcome some limitations of traditional annealing, which can result in increased mechanical properties. However, an increase in crystallization also leads to material embrittlement.