A new lightweight structure that snaps together in tiny blocks like the bricks of a has been developed by researchers at MIT. Researchers are saying the new material may revolutionize the assembly of large structures such as aircraft, spacecraft, and dikes and levees. Neil Gershenfeld, director of MIT’s Center for Bits and Atoms, compares the structure, made from tiny, identical, interlocking parts, to chainmail.
The parts, based on a novel geometry that study co-author Kenneth Cheung developed with Gershenfeld, form a structure that is 10 times stiffer for a given weight than existing ultralight materials. But this new structure can also be taken apart and reassembled easily, in order to repair damage, or to recycle the parts into a different configuration, something that cannot be done readily with current composite materials.
Cellular Composite 3D Printing
The individual parts are mass-producable. The researchers are developing a robotic assembly system to put them together into airplane wings, fuselages, bridges or rockets. Three fields of research and brought together in the new design, says Gershenfeld: fiber composites, cellular materials made with porous cells and additive manufacturing, also known as 3-D printing, where structures are built by depositing rather than removing material.
In today’s composite materials, used now in products ranging from golf clubs and tennis rackets to the components of Boeing’s new 787 commercial jet, each piece is manufactured as a integrated unit. Fabrication of large structures, such as an airplane fuselage, requires large factories where fibers and resins can be wound and parts heat-cured as a whole, minimizing the number of separate pieces that must be joined in final assembly. That requirement meant, for example, Boeing’s suppliers have had to build massive facilities to build major parts for the 787.
This new technique allows much less material to carry a given stress load. That lower weight could not only significantly lower fuel use and operating costs in vehicles, but also reduce the costs of construction and assembly, at the same time as allowing better design flexibility.
Can You 3-D Print an Airplane?
Gershenfeld says the concept came as a response to the question, “Can you 3-D print an airplane?” While he and Cheung understood that 3-D printing was an unreasonable approach at such a large scale, they wondered if it might be possible instead to use the discrete digital materials that they were studying.
“This satisfies the spirit of the question,” Gershenfeld says, “but it’s assembled rather than printed.” The researchers are now developing an assembler robot that can crawl over the surface of a growing structure, adding pieces one by one to the growing structure.
Cracks and structural failures tend to start at the joints between large components in traditional composite manufacturing. Although these new structures are created via linking many small composite fiber loops, Cheung and Gershenfeld show that they act more like an elastic solid, with a modulus (stiffness), equal to that of much heavier traditional structures. This is because forces are conveyed through the structures inside the pieces and distributed across the lattice structure.
Massively Redundant Cubic Lattice
Further, when composite materials are stressed beyond their breaking point, they are prone to abrupt failures and at large scale. But this modular system tends to fail incrementally, so it would be more reliable and more easily repaired, the researchers say. “It’s a massively redundant system,” Gershenfeld says.
The structure is made of flat, cruciform-shaped composite pieces clipped into a cubic lattice of octahedral cells. This structure is called a “cuboct” and is similar to the crystal structure of the mineral perovskite, a major part of the Earth’s crust.
While the individual components can be disassembled for repairs or recycling, there’s no risk of them falling apart on their own, the researchers explain. Like the buckle on a seat belt, they are designed to be strong in the directions of forces that might be applied in normal use, and require pressure in an entirely different direction in order to be released.
Airbus’ program director of innovation, Alain Fontaine, says this new approach to building structures “is really disruptive. It opens interesting opportunities in the way to design and manufacture aerostructures.” These technologies, he says, “can open the door to other opportunities” and have major potential to lower manufacturing costs.
Reversibly Assembled Cellular Composite Materials
Kenneth C. Cheung, Neil Gershenfeld
Science, DOI: 10.1126/science.1240889
Photo courtesy Kenneth Cheung