A Low-Energy "Thermal Trigger" Sets These 3D-Printed Shapes A-Morphing — In Space

A pair of researchers from the University of Illinois Urbana-Champaign's Grainger College of Engineering have come up with a way to 3D print structures that could morph their shapes when deployed in space — with a low-energy "thermal trigger."

"In this case, our collaborators in the Beckman Institute developed a recipe for a pure resin system that's very energy efficient. And we have a 3D printer that can print commercial aerospace-grade composite structures. I think the breakthrough was combining those two things into one," explains first author Ivan Wu, who worked with supervisor and senior author Jeff Baur on the project. "We used the continuous carbon fiber 3D printer to print bundles of fiber, with each fiber about the diameter of a human hair. As the fiber bundles are drawn by the printer onto a bed, they are compressed and exposed to ultraviolet light, which partially cures them."

The partially-cured material is then frozen, and could be shipped into space in a much smaller package than if it were printed at full scale. Once there, it requires only a small amount of heat to provide a "thermal trigger" and complete the curing process — with the embedded fibers pulling it into the final shape desired.

"For me, the first challenge was to solve the inverse problem," Wu says of the shape design process. "You have a design for the 3D shape you want, but what is the 2D pattern to print that results in that shape? I had to write mathematical equations to describe the shapes to print the exact pattern. This study solved that problem."

The idea of heat-curing objects in space isn't new, but previous efforts have encountered a scaling problem: the larger the object, the more heat is required — and thus more energy. The team's approach, though, is highly scalable: the researchers compare the "thermal trigger" to the application of a match to a sheet of paper, as setting off a chemical reaction which is self-sustaining long after the original energy input is spent.

To prove the concept, the team designed and built five different shapes: a spiral cylinder, a twist, a cone, a saddle, and a parabolic dish. "Together, they show the diversity of shapes we can make," Wu says. "But I think the one that's most interesting and applicable is the parabolic dish, which mimics the smooth, curved shape that’s needed for deployable satellites."

The only drawback to the pair's approach: the more you want the shape to morph on curing, the fewer fibers you can include — which makes the finished object less stiff than would be typically be required, the exact opposite problem to existing approaches to the same problem. The proposed fix: using that shape as a mold for a higher-stiffness composite, formed to its shape. "We show in our work that this process can be repeated numerous times," Wu notes, "without damage to the mold or deviation from the initial morphed shape."

The team's work has been published in the journal Additive Manufacturing under closed-access terms.