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.
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This content will become publicly available on December 1, 2024
High through-thickness thermal conductivity of 3D-printed composites via rotational direct ink writing
Composites printed using material extrusion additive manufacturing (AM) typically exhibit alignment of high-
aspect-ratio reinforcements parallel to the print direction. This alignment leads to highly anisotropic stiffness,
strength, and transport properties. In many cases, it would be desirable to increase mechanical and transport
properties transverse to the print direction, for example, in 3D-printed heat sinks or heat exchangers where heat
must be moved efficiently between printed roads or layers. Rotational direct ink writing (RDIW), where the
deposition nozzle simultaneously rotates and translates during deposition, provides a method to reorient fibers
transverse to the print direction during the printing process. In the present work, carbon fiber-reinforced epoxy
composites were printed by RDIW with a range of nozzle rotation rates and the in-plane and through-thickness
thermal conductivity was measured. In addition, the orientation of carbon fiber (CF) in the composites was
measured using optical microscopy and image analysis, from which second-order fiber orientation tensors were
calculated. These results showed that the orientation of CF became less anisotropic as nozzle rotation rate
increased, leading to increased through-thickness thermal conductivity, which increased by 40% at the highest
rotation rate. The orientation tensors also showed that RDIW was more effective at reorienting fibers within the
in-plane transverse direction compared to the through-thickness transverse direction. The results presented here
demonstrate that a current weakness of material extrusion AM composites—poor thermal conductivity in the
through-thickness direction—can be significantly improved with RDIW.
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- Award ID(s):
- 1825815
- NSF-PAR ID:
- 10482724
- Publisher / Repository:
- Elsevier B.V.
- Date Published:
- Journal Name:
- Additive Manufacturing Letters
- Volume:
- 7
- Issue:
- C
- ISSN:
- 2772-3690
- Page Range / eLocation ID:
- 100167
- Subject(s) / Keyword(s):
- Additive manufacturing Composites Thermal conductivity 3D printing Rotational direct ink writing Fiber orientation Epoxy Carbon fiber
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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