The rolyPOLY project started as a larger research initiative at Ball State University in Muncie, Ind., known as the One Day House – a robust, intelligent, adaptable yet affordable housing system made by robotic fabrication of composites. Most of the installations were small, recalls Andrew John Wit, who started the project at Ball State. When Wit came to Temple, he and Simon Kim, an assistant professor at the University of Pennsylvania in Philadelphia, decided to see how big they could make the structure with the tools at their disposal.
The rolyPOLY was a collaborative effort between Wit, Kim and Mariana Ibañez, an associate professor at Harvard University in Cambridge, Mass. To make the shelter, the team wound 12,000-strand prepreg CFRP tow around a pre-fabricated modular frame made with steel modules that can be easily recycled or reconfigured. However, Wit says the frame wasn’t optimal, so they developed a robotic winding pattern consisting of three repeating steps: peak winding (to generate a stable CFRP framework), valley winding (to connect the structure’s low points and tension the initial CFRP layers) and spiral winding (a high-tension third layer of CFRP on all the intersecting panel edges, minimizing layer delamination).
“In order to achieve a similar level of structural stability that you would get from a vacuum bag or a really robust cored formwork, we had to create a system that required double curvature of the surfaces,” Wit says. “Every surface had to be double curved to allow for a really strong overlap of material.” After lots of testing, the team realized it needed all three different winding patterns to collapse the CFRP tow fibers onto each other.
After completing one full winding cycle, the winding direction was flipped 180 degrees and restarted. After winding, the structure was baked in a 6.5 x 5 x 5-foot gas-fired kiln at 260 F. Upon cooling, the structure’s steel formwork was removed from the composite shell.
The researchers chose the prepreg CFRP due to its workability, consistency, stability, curing attributes, minimal toxicity and strength. However, a literal sticking point with Wit was the team’s ability to reduce waste.
“We could work with [the prepregs] more hands-on without having to worry about wasting resin and dripping resin all over the place,” Wit explains. “Also, we could specify the exact resin consistency that we wanted in the tow. [During the winding process], the fibers were tacky and would stick to each other pretty well, but there weren’t pools of resin, which made it a really simple, yet interesting material to use.”