MIT researchers have invented a new digital material whose block like design allows the assembly of huge structures like towers, spacecraft and airplanes by snapping blocks together. Parts 10 times stiffer than existing ultralight materials can be assembled instead of engineered, by small robots crawling over the structure adding pieces of material bit by bit. Not only does tinkertoy-like block construction method enable any structure to be assembled and disassembled easily, it's also possible to recycle them into entirely new configurations.

"You could take apart a bridge and reconfigure it into a tower or building, or take a boat and reconfigure it into a dock, or maybe a different type of boat," Kenneth Cheung, a post-doctoral associate, at the Center for Bits and Atoms (CBA), MIT tells Gizmag.

Cheung and Neil Gershenfeld, director of CBA, hit upon the idea of using digital materials they were studying for manufacturing purposes when they asked themselves the question "Can you 3D print an airplane?" Realizing it was impossible to print out such large structures using traditional methods, they wondered if it might be possible to assemble them instead. The new material, called reversibly assembled cellular composite, combines three research areas: cellular materials, fiber composites and additive manufacturing. Its interlocking chainmail structure allows parts to be incrementally added or removed.

Cheung compares the material to amino acids, the fundamental building blocks of animals. "There are not very many of these, but the diversity of organisms that can be made from the same set of building blocks is easy to appreciate," he tells us. "The term digital material refers to a material that uses this building block approach. Many toys satisfy this definition in some ways, like Lego and K'nex. One thing that this can allow us to do is to take the precision with which we can make small things, and build, almost arbitrarily, bigger things at the same or with better precision, by connecting the small things. Consider the precision of a structure built out of Lego, of any size, compared to the precision of the average six-year-old building that structure."

A sample of cellular composite material is set in a load-testing machine to measure mechanical properties such as strength and stiffness (Photo: Kenneth Cheung)

Easily mass produced, research into a robotic system that can assemble it into structures both simple and complex is currently underway. Cheung envisages small families of simple insect-like robots climbing over structures to carry out their assigned functions. "For instance, a robot that inspects pieces for damage can be separate from the robot that removes damaged pieces, which can be separate from the robot that moves pieces around the structure, which can be separate from the robot that installs new pieces," he explains.

Repairing damaged parts becomes easy too. For instance, a damaged robotic arm could be detached from the rest of the robot, repaired and fixed in place, similar to how you would take off a glove and put it back on. Instead of closing down bridges that develop internal cracks, robots could simply scramble through the structure's interior, repairing any damage along the way

The team hopes that the material will revolutionize existing manufacturing processes. Currently making a part such as an airplane wing involves processing and heat curing materials to create separate components that are finally joined together. Entire factories are devoted to assembling a plane as big as a Boeing 787. However, with the aid of the new material, one could build an airplane with perhaps more parts, but fewer unique ones, making repairs and replacements easier.

"A commercial plane might have 6 million parts, half of which are rivets," Cheung tells Gizmag. "Of the remaining parts, perhaps around a million of them are unique designs. A similarly sized plane made from digital materials might have 10-20 million parts, but vastly fewer unique part designs, maybe four or five structural part types, which can be used or reused in an exponential variety of different plane designs."

Close-up view of cellular composite material sample (Image: Kenneth Cheung)

Moreover, traditional structures containing many large parts tend to develop structural failures at the joints. Additionally if a particular part experiences a lot of stress, it tends to break apart quite spectacularly. However, a part developed with the new material will only develop cracks within its structure and not at the joints which are designed to be stronger than the rest of the system, the researchers claim. Even when such a part is stressed unnaturally, its internal structure will, they say, distribute forces across the internal lattices, so that only small components in the system fail incrementally; such parts would be more reliable, they claim.

"With regard to digital materials, this kind of system is potentially useful for making almost any engineered structure," Cheung tells Gizmag."From a manufacturing point of view, it's like the difference between having paint and a brush to paint a picture, versus a digital printer. You will of course need high enough resolution to suit a particular task, but then the diversity of possible output is very comprehensive."

The block type assembly process also makes it possible to create shape morphing parts. For instance, instead of changing an airplane's wing shape through cables or hinge and sliding mechanisms, the entire wing could morph in a controlled way.

Not only does it permit more design freedom, but it will also reduce construction costs and the overall weight of structures built with it, which could lead to lower operating and fuel costs. "Weight reductions from new systems that include composite materials are estimated to result in around 30 percent fuel savings for recently introduced passenger aircraft," says Cheung.

Cheung who has been working on digital materials for many years, states that automated assemblers need to be developed first before it's possible to see personal gadgets and appliances made from the material in the market. "It will be very exciting," Cheung tells us. "You will be able to do things like reconfigure old devices into new designs.

Sarah Hovsepian presently at NASA’s Ames Research Center and MIT undergraduate Joseph Kim were also part of the project, which was supported by the sponsors of the CBA, Spirit Aerosystems and the Defense Advanced Research Projects Agency. A paper describing the material also appeared in Science.

Source: MIT