Carbon Fiber 3D Printing, Part Seven: R&D

March 4, 2020 by Michael Molitch-Hou 3D Printing Carbon Fiber Series

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So far in our series on 3D printing carbon fiber and other reinforcement materials, we’ve discussed much about the present state of the technology, including large-scale composite deposition and some of the most recent startup developments. What we have yet to cover is the state of the research around 3D printing carbon fiber, which will ultimately play an important role in the trajectory of the technology.

Among the areas of research dedicated to carbon fiber 3D printing is the characterization of printed parts reinforced with carbon fiber, both continuous and chopped. A team from the US Army Tank-Automotive Research Development, and Engineering Center studied the strength of continuous carbon fiber reinforced parts printed on a Mark Two 3D printer.

Schematic of specimens on print bed to show specimen placement and fiber orientation (where relevant).

The researchers concluded that reinforced parts reinforced in-plane and aligned with the orientation of the carbon fibers (Group 2 in the image above) were much stronger than non-reinforced parts (Group 1); that parts reinforced in-plane but perpendicular to the orientation of the fibers (Group 3) was weaker than when aligned with the fiber; and that parts were weakest when printed out of plane and perpendicular to the orientation of the fibers (Group 4).

As for chopped carbon fiber reinforcement, some studies, including one study from the University of New South Wales at the Australian Defence Force Academy, have determined that filaments filled with chopped carbon fiber or carbon nanotubes suffer from voids and defects that render printed objects weaker and more ductile than filaments without carbon filler.

A team from the University of Chinese Academy of Science found that, using a high-temperature 3D printer (the Funmat HT) to print with PEEK reinforced with chopped carbon fiber did increase the strength of the parts significantly. However, they also found increased porosity in these parts.

Shape memory performance test with different fiber contents.

Another area being explored is the variety of composite materials that can be 3D printed using carbon fiber reinforcement, including shape memory polymers, epoxies, and nanocellulose. Reinforcing shape memory polymers with carbon fiber makes it possible to add stiffness and strength to otherwise weak, but highly malleable materials. Reinforcing an epoxy with carbon fiber is considered one way to overcome the weakness and poor interlayer bonding associated with printed thermoplastics because the irreversible chemical bonds formed after curing a thermoset can bring greater strength to the material. A mixture of carbon nanotubes and nanocellulose can result in a material with high electrical conductivity and high mechanical strength for potential use in creating low-cost, high-performance wearable electronics.

A Schematic of acoustic focusing device. B Diagram of forces aligning and pushing fibers to the center of a channel as the result of a standing pressure half-wave. C,D,E Time-lapse of fibers patterned into parallel bundles by acoustic focusing in photopolymer resin, reaching equilibrium positions after 5-6 seconds. F Illustration and micrograph of an unpatterned composite with carbon fibers dispersed in acrylate resin (0.36v% carbon fiber). G Illustration and micrograph of a patterned carbon-fiber in acrylate composite (0.36v% carbon fiber) fabricated with acoustic focusing.

There have also been numerous studies on developing new ways for 3D printing carbon fiber, from more straightforward laser powder bed fusion techniques to acoustic focusing methods for orienting short carbon fibers. A team of engineers from USC Viterbi School of Engineering deployed an electrical field to align carbon fibers in an attempt to mimic the structure of a lobster shell.

Closely related to carbon fiber is graphene, the single-Carbon-atom-thin wonder material that is 100 times stronger than steel. Many institutions are researching the possibilities of 3D printing graphene, for the possibility of creating electronics, electrical devices and even biomedical implants. This includes supercapacitors, that is energy storage devices that charge very rapidly and can retain their storage capacity through tens of thousands of charge cycles.

Because many startups are spun out of research endeavors, there’s no telling when these technologies will be commercialized. Fortify, for instance, was born out of the Directed Assembly of Particles and Suspensions lab at Northeastern University and its method for magnetically orienting carbon fibers and other reinforcement materials sounds just like some of the other futuristic-sounding tech described in this article. In other words, the technology now being developed in the lab may make it into the real world any day now.