Whats the difference between the Eiffel Tower and the Washington Monument? Both structures soar to impressive heights, and each was the worlds tallest building when completed. But the Washington Monument is a massive stone structure, while the Eiffel Tower achieves similar strength using a lattice of steel beams and struts that is mostly open air, gaining its strength from the geometric arrangement of those elements. Now engineers at MIT and Lawrence Livermore National Laboratory (LLNL) have devised a way to translate that airy, yet remarkably strong, structure down to the microscale - designing a system that could be fabricated from a variety of materials, such as metals or polymers, and that may set new records for stiffness for a given weight. The new design is based on the use of microlattices with nanoscale features, combining great stiffness and strength with ultralow density. The actual production of such materials is made possible by a high-precision 3-D printing process called projection microstereolithography. Normally, stiffness and strength declines with the density of any material; thats why when bone density decreases, fractures become more likely. But using the right mathematically determined structures to distribute and direct the loads, the lighter structure can maintain its strength. It is similar to the way Eiffel tower gets its strenth by the way of the arrangement of vertical, horizontal, and diagonal beams. This newly invented material is among the lightest in the world. However, because of its microarchitected layout, it performs with four orders of magnitude higher stiffness than unstructured materials, like aerogels, at a comparable density. These matericals can easily withstand a load of more than 160,000 times their own weight. So far, the researchers at MIT have tested the process using three engineering materials — metal, ceramic, and polymer — and all showed the same properties of being stiff at light weight. By Using light to imprint features onto polymer or plastic,the researchers disproved the established diffraction limit, and they proved first time that it is possible to print sub-wavelength features one-hundredth the thickness of a human hair. This discovery allows manufacturers to imprint finer features into items such as DVDs to significantly improve storage capabilities, or to probe the traffic of protein or DNA. This approach could be useful anywhere theres a need for a combination of high stiffness (for load bearing), high strength, and light weight — such as in structures to be deployed in space, where every bit of weight adds significantly to the cost of launch. But the researcher (Nicholas Fang) says there may also be applications at smaller scale, such as in batteries for portable devices, where reduced weight is also highly desirable. Another property of these materials is that they conduct sound and elastic waves very uniformly, meaning they could lead to new acoustic metamaterials, that could help control how waves bend over a curved surface. As this research was funded by DARPA, it could also end up on robots and drones. #technology #MIT
Posted on: Fri, 26 Sep 2014 20:48:50 +0000
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