Lawrence Livermore scientists James Lewicki (left) and Jennifer Rodriguez examine a 3D-printed carbon fiber part created using a direct-ink writing process developed at LLNL. (Photos by Kate Hunts/LLNL)
For the first time researchers at Lawrence Livermore National Laboratory (LLNL) have 3D printed aerospace-grade carbon fiber composites, paving the way for better control and optimization of the lightweight material that is stronger than steel.
The research exhibits a "significant advance" in the progress of micro-extrusion 3D printing techniques for carbon fiber, the authors stated. Details of the research have been published by the journal Nature Scientific Reports online on February 28.
The mantra is 'if you could make everything out of carbon fiber, you would' -- it's potentially the ultimate material. It's been waiting in the wings for years because it's so difficult to make in complex shapes. But with 3D printing, you could potentially make anything out of carbon fiber.
Jim Lewicki, Chief Investigator, LLNL
Although it is lightweight, carbon fiber is still a stiff and strong material with a high resistance to temperature, making the composite material in demand in the automotive, aerospace, and defense industries, and sports such as motorcycle racing and surfing.
Carbon fiber composites are commonly fabricated one of two ways - by weaving the fibers together like a wicker basket or physically twisting the filaments around a mandrel, resulting in end products that are limited to either cylindrical or flat shapes, Lewicki said. Manufacturers also tend to overcompensate with material due to performance apprehensions, making the parts costlier, heavier, and more wasteful than required.
However, the LLNL researchers reported printing numerous complex 3D structures using a customized Direct Ink Writing (DIW) 3D printing process. Lewicki and his team also created and patented a new chemistry that can cure the material within seconds rather than hours, and used the Lab's high performance computing capabilities to build accurate models of the flow of carbon fiber filaments.
How we got past the clogging was through simulation. This has been successful in large part because of the computational models.
Lewicki, Chief Investigator, LLNL
Computational modeling was performed on LLNL's supercomputers by a team of engineers who had to imitate thousands of carbon fibers as they emerged from the ink nozzle to discover how to ideally align them during the process.
"We developed a numerical code to simulate a non-Newtonian liquid polymer resin with a dispersion of carbon fibers. With this code, we can simulate evolution of the fiber orientations in 3D under different printing conditions," said fluid analyst Yuliya Kanarska. "We were able to find the optimal fiber length and optimal performance, but it's still a work in progress. Ongoing efforts are related to achieving even better alignment of the fibers by applying magnetic forces to stabilize them."
The ability to 3D print provides the carbon fiber with new degrees of freedom, researchers said, allowing them to have control over the parts' mesostructure. The material is conductive as well; enabling directed thermal channeling within a structure.
The resulting material could be used to build satellite components that are insulated on one side and do not need to be rotated in space, high-performance airplane wings, or wearables that can absorb heat from the body but do not allow it in, the researchers said.
A big breakthrough for this technology is the development of custom carbon fiber-filled inks with thermoset matrix materials. For example, epoxy and cyanate ester are carefully designed for our printing process, yet also provide enhanced mechanical and thermal performance compared to thermoplastic counterparts that are found in some commercially available carbon fiber 3D printing technologies, such as nylon and ABS (a common thermoplastic). This advance will enable a broad range of applications in aerospace, transportation and defense.
Eric Duoss, Researcher, LLNL
The direct ink writing process also allows printing of parts with all the carbon fibers going the same direction within the microstructures, thus allowing them to perform better than similar materials developed with other techniques done with random alignment. Through this process, the researchers stated they are able to use two-thirds less carbon fiber and obtain the same material properties from the end part.
Going forward, the researchers will focus on optimizing the process, examining the best places to lay down the carbon fiber to heighten performance. There have been talks with commercial, defense and aerospace partners to move the development of the technology forward.
Other Lab researchers included on the paper are Jennifer Rodriguez, Cheng Zhu, Marcus Worsley, Amanda Wu, John Horn, Jason Ortega, William Elmer, Ryan Hensleigh, Ryan Fellini and Michael King.
The study was funded by the Laboratory Directed Research and Development program.
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