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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Hybrid Metal-Organic Frameworks/Carbon Fibers Reinforcements for Additively Manufactured Composites
Additively manufactured (AM) composites based on short carbon fibers possess strength and stiffness far less than their continuous fiber counterparts due to the fiber’s small aspect ratio and inadequate interfaces with the epoxy matrix. This investigation presents a route for preparing hybrid reinforcements for AM that comprise short carbon fibers and nickel-based metal-organic frameworks (Ni-MOFs). The porous MOFs furnish the fibers with tremendous surface area. Additionally, the MOFs growth process is non-destructive to the fibers and easily scalable. This investigation also demonstrates the viability of using Ni-based MOFs as a catalyst for growing multi-walled carbon nanotubes (MWCNTs) on carbon fibers. The changes to the fiber were examined via electron microscopy, X-ray scattering techniques, and Fourier-transform infrared spectroscopy (FTIR). The thermal stabilities were probed by thermogravimetric analysis (TGA). Tensile and dynamic mechanical analysis (DMA) tests were utilized to explore the effect of MOFs on the mechanical properties of 3D-printed composites. Composites with MOFs exhibited improvements in stiffness and strength by 30.2% and 19.0%, respectively. The MOFs enhanced the damping parameter by 700%.
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- NSF-PAR ID:
- 10426561
- Date Published:
- Journal Name:
- Nanomaterials
- Volume:
- 13
- Issue:
- 5
- ISSN:
- 2079-4991
- Page Range / eLocation ID:
- 944
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/nano13050944
