Effects of fiber surface treatment and nozzle geometry in structural properties of additively manufactured two-phase composites

摘要

The effects of fiber surface functionalization, annealing, and nozzle geometry on the structural properties of additively manufactured (AM) carbon fiber (CF)/polylactic acid (PLA) composites have been investigated. The structural properties such as tensile and bead-bonding properties were studied. The specimens were 3D printed using fused deposition modeling (FDM) based AM. Both conventional circular extrusion nozzle and custom-made square nozzle were used in this study. The square nozzle geometry was selected based on computational modeling results of two-phase melt extrusion process. The bead architecture resulting from a square nozzle enhances the bead-bonding area and reduces the void contents. The neat PLA and 5 wt. % CF/PLA composite filaments were extruded in the laboratory to feed into a FDM system to print tensile and inter-bead bonding specimens. All the printed specimens were tested in the laboratory following ASTM designated test methods. An increase in both tensile and inter-bead bond strength of about 8% and 11.2%, respectively was observed for the specimens extruded with the square nozzle. The post manufacturing thermal treatment on the functionalized fiber reinforced composite showed further improvement in both tensile strength and modulus by about 11.2% and 70%, respectively. Such treatment is also seen to enhance the bead-bonding strength of approximately 7.6%. The microstructures of the specimens extruded through circular and square nozzles were examined using optical microscopy. The bead-bonding architecture was analyzed through optical microscopy and the fracture mechanisms were studied through scanning electron microscopy (SEM) examination. Fractography revealed different failure modes with high fiber orientation along the printing direction. Finally, the presence of void contents, de-bonding, fiber pullout, and their influence in the overall performance of the composites are described.