Jan 9, 2017 | By Benedict
A team of MIT researchers has used a multi-material 3D printer to investigate one of the strongest lightweight materials ever. By compressing and fusing flakes of graphene, the researchers were able to create a material with 5 percent the density and 10 times the strength of steel.
When attempting to create ultra-strong 3D structures using modern manufacturing techniques, scientists are increasingly finding that the shape and form of a structure is just as important for achieving strength as the material itself. And with technologies like 3D printing allowing the brightest material engineers to experiment with completely new shapes and forms, structures are only getting stronger and stronger. A group of MIT researchers recently carried out some exciting experiments with graphene, widely considered to be the strongest of materials in 2D form, in which they were able to investigate why graphene is so strong.
The MIT researchers, whose work was published last week in Science Advances, were able to compress small flakes of graphene using a combination of heat and pressure, eventually producing a strong, stable structure that somewhat resembles coral. But after creating this incredibly strong, compressed form of graphene, the scientists realized something very important: it was the unusual, coral-like shape of this compressed graphene that was making it so strong, rather than the properties of the material itself. Therefore, by replicating the 3D form with other, cheaper materials, such as plastics, the scientists could achieve graphene-like strength on a shoestring budget.
The scientists behind the research found that, when compressing the graphene flakes into an ultra-strong form, the material behaved a bit like folded paper: paper, when unfolded, can be easily crumpled up, but when it is rolled into a tube or folded into a smaller size, its strength increases massively. Likewise, the new compressed arrangement of the graphene flakes creates a much stronger form than the uncompressed arrangement. Once they realized this pattern, the researchers wanted to see just how strong they could make the material: “We wanted to see what’s the limit—what’s the strongest possible material we can produce,” said Zhao Qin, a CEE research scientist at MIT.
When they pushed their compressed graphene structures to the limit, the researchers found they could make an incredibly strong material—one with five percent the density of steel, but 10 times the strength. Then, by analyzing the geometric arrangement of the compressed graphene flakes, the researchers were able to partially recreate the strong material using a 3D printer. At first, they hoped they might be able to create a 3D printed graphene structure that was lighter than air, and could be used as a stronger alternative to helium in balloons. However, tests showed that such a structure would collapse from surrounding air pressure.
One of the most important discoveries made by the researchers was the realization that the ultra-strong geometric configuration of the graphene could be recreated with other materials, in order to either save money or take advantage of properties found in other materials. “You could either use the real graphene material or use the geometry we discovered with other materials, like polymers or metals,” said Markus Buehler, head of MIT’s Department of Civil and Environmental Engineering (CEE) and the McAfee Professor of Engineering. “You can replace the material itself with anything.”
When subjected to heat and pressure, graphene forms into geometric shapes that are round but full of holes. These shapes, known as gyroids, are incredibly difficult to recreate synthetically, but the team used 3D printed models of the structure, enlarged to thousands of times their natural size, for testing purposes. While these 3D printed models were not as strong as the actual compressed graphene, researchers say that polymer or metal particles could be used as templates, coated with graphene by chemical vapor deposit before heat and pressure treatments, and then chemically or physically remove the polymer or metal phases to leave 3D graphene in the gyroid form.
Ultimately, the discoveries made by the MIT researchers could have implications across many fields. For example, concrete structures such as bridges could potentially be made with a similar porous geometry to that found in the graphene, while the tiny pores of the geometry could also prove useful in filtration systems, for either water or chemical processing.
Posted in 3D Printing Materials
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