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Short carbon fiber-reinforced polymer composites are widely employed in additive manufacturing (AM) techniques, including Large Area Additive Manufacturing (LAAM) polymer extrusion-deposition, due to their superior mechanical properties compared to neat polymers. The mechanical and thermal properties of these composites are significantly influenced by factors such as fiber volume fraction, orientation, length, and distribution, and void distribution and volume fraction within the microstructure of the printed beads. This paper presents an experimental study that aims to quantitatively assess the relationship between void volume fraction and fiber orientation within the microstructure of both single freely extruded strands and single deposited beads of Short Carbon Fiber reinforced Acrylonitrile Butadiene Styrene (SCF/ABS) manufactured via a LAAM system. The study employs high-resolution 3D microcomputed tomography (μCT) to evaluate the fiber orientation, fiber volume fraction, and void volume fraction within the microstructure of the SCF/ABS composite parts. The findings demonstrate that the print direction 𝐴zz component of the fiber orientation tensor in the regions near the edges of the single freely extruded strand is higher than those near the center, likely due to increased nozzle shear rate near the wall. Furthermore, within a single deposited bead on the print bed, the 𝐴zz component varies throughout the microstructure. Measurements also show that regions with relatively higher void volume fraction have a corresponding lower fiber 𝐴zz and fiber volume fraction for both the single freely extruded strand and the single deposited bead. 

Short carbon fiber-reinforced polymer composite structures produced using Large Area Additive Manufacturing (LAAM) have garnered significant attention due to the design flexibility, energy savings, and materials selection associated with this process. However, the physical and mechanical properties of the additively manufactured composite parts often fall below expectations due to void formation between printed beads and within the microstructure of individual beads. This study aims to investigate the effect of bed temperature on the microstructure within the beads of two-layer Short Carbon Fiber reinforced Acrylonitrile Butadiene Styrene (SCF/ABS) beads manufactured via the LAAM system. This study employs high-resolution 3D micro-computed tomography (μCT) to evaluate the void shape and distribution within the microstructure of composite parts printed at various bed temperatures. The results of this study demonstrate substantial variation in the void volume fraction among four bead sets deposited at different print bed temperatures. Moreover, within each part, a noticeable discrepancy in void volume fraction is observed between the top and bottom bead of the two-bead test samples. Preliminary results indicate that increasing the bed temperature from 25°C to 75°C reduces void volume fraction within the microstructure of the composite parts. However, an opposite trend emerges when the bed temperature is further increased to 100°C, increasing void volume fraction, which needs further investigation to understand. This study also evaluated the void shapes through the calculation of their sphericity. The preliminary results reveal that as the bed temperature increases from 25°C to 75°C, the voids exhibit higher sphericity within the printed parts as the interconnected voids decrease.