20 August 2013

MIT develops carbon fiber ‘Lego bricks’ that can be fashioned into airplanes, rockets, bridges


Materials engineers at MIT have created the carbon fiber equivalent of Lego bricks or K’Nex — interlocking carbon fiber blocks that can be formed into large structures that are 10 times stiffer than comparable ultralight materials. These structures could be mass-produced by automated robots, and fashioned into airplane and rocket fuselages, wings, and bridges, among other things. Interestingly, unlike almost every other object made from composite materials, objects made from MIT’s new structure can be easily disassembled or have individual “bricks” replaced when they break.

“Can you 3D-print an airplane?” That is the question that MIT’s Neil Gershenfeld asked himself. As it turns out, 3D printing is a bit impractical for creating large objects like airplane wings or fuselages, but Gershenfeld working with Kenneth Cheung found that it was perfect for creating components that can then be fashioned into larger objects.



Each of the bricks is fashioned out of carbon fiber impregnated with epoxy resin, formed into the shape of a flat X. Each X has a hole in the middle, which the leg of another X slots into (pictured above). The end result is a very stiff structure of vertex-connected octahedrons, or, as the researchers call them, “cubocts.” These cubocts can be added, removed, and reoriented to build different structures with different strengths (one might be resistant to crushing, while one might be difficult to twist). To put it into numbers, structures made out of these bricks are capable of withstanding 12.3 megapascals of compressive force (pressure), with a very low density of 7.2 milligrams per cubic centimeter. MIT says this is 10 times stiffer than other materials of the same density.

Irrespective of physical strength, the main advantage of these carbon fiber bricks is that they can be readily assembled, disassembled, or even replaced if they’re damaged. One of the biggest weaknesses of composite materials (such as carbon fiber, glass fiber, etc.) is that they are generally fashioned into huge, monolithic pieces. Not only is it hard and expensive to create something that is very large (you need equally large machines and tools to handle the creation of them), but it’s generally very hard to fix any damage that’s sustained. As you may have heard, one of the reasons the Boeing 787 Dreamliner is so efficient is due to its use of lightweight composite materials — but whereas metal-bodied planes can be fixed with sheet steel and rivets, it’s very hard to repair damage to a composite fuselage.




Moving forward, the Cheung and Gershenfeld are now building a robotic system that can assemble their carbon fiber bricks into useful structures. By weaving in different bricks, the researchers believe they can create structures that are strong in more than one direction. Of course, if we combine these two advances, there’s always the possibility of a material that can reassemble itself on the fly, depending on the situation and which forces it needs to endure. Can you say… Transformers, transform?

Now read: Real life “Constructicon” quadcopter robots being developed

Research paper: DOI: 10.1126/science.1240889 – “Reversibly Assembled Cellular Composite Materials”

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