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Lattice structure absorbs vibrations

Strong vibrations from a bus engine can be felt uncomfortably through the seats. Similarly, vibrations from the propellers or rotors in propeller aircraft and helicopters can make the flight bumpy and loud. They also lead to increased fatigue damage of the aircraft and its components. Engineers have therefore sought to prevent such vibrations in machines, vehicles, and aircraft. A new three-dimensional lattice structure developed by ETH scientists could now expand the possibilities of vibration absorption. Led by Chiara Daraio, Professor of Mechanics and Materials, the researchers made the structure with a lattice spacing of around 3.5 mm out of plastic using a 3D printer. Inside the lattice they embedded steel cubes that are somewhat smaller than dice and act as resonators. "Instead of the vibrations traveling through the whole structure, they are trapped by the steel cubes and the inner plastic grid rods, so the other end of the structure does not move," explains Kathryn Matlack, a postdoc in Daraio's group.The vibration-absorbing structure is rigid and thus can be used as a load-bearing component in rotors and propellers. It also offers another advantage. Compared to existing soft absorption materials, it can absorb a much wider range of vibrations, both fast and slow, and is particularly good at absorbing relatively slow vibrations. "The structure can be designed to absorb vibrations with oscillations of a few hundred to a few tens of thousand times per second (Hertz)," says Daraio. "This includes vibrations in the audible range. In engineering practice, these are the most undesirable, as they cause environmental noise pollution and reduce the energy efficiency of machines and vehicles."In theory, it would be possible to build such a construction out of aluminum and other lightweight metals instead of plastic, says Matlack. In principle, it would just require a combination of lightweight material, structured in a lattice geometry, and embedded resonators with a larger mass density. The geometry of the lattice structure and the resonators would need to be optimally aligned to the anticipated vibrations.The vibration absorbers are essentially ready for technical applications, says Matlack, but they are limited insofar as 3D printing technology is mostly geared toward small-scale production, and material properties, such as the load-bearing capacity, cannot yet match those of components manufactured with traditional methods. Once this technology is ready for industrial use, there is nothing standing in the way of a broader application. A further application could be in wind turbine rotors, where minimizing vibrations would increase efficiency. The technology could also conceivably be used in vehicle and aircraft construction as well as rockets.

Posted in: News, Aerospace

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Carbon nanotube 'stitches' make stronger, lighter composites

The newest Airbus and Boeing passenger jets flying today are made primarily from advanced composite materials such as carbon fiber reinforced plastic – extremely light, durable materials that reduce the overall weight of the plane by as much as 20 percent compared to aluminum-bodied planes. Such lightweight airframes translate directly to fuel savings, which is a major point in advanced composites' favor.But composite materials are also surprisingly vulnerable: While aluminum can withstand relatively large impacts before cracking, the many layers in composites can break apart due to relatively small impacts – a drawback that is considered the material's Achilles' heel.Now MIT aerospace engineers have found a way to bond composite layers in such a way that the resulting material is substantially stronger and more resistant to damage than other advanced composites.The researchers fastened the layers of composite materials together using carbon nanotubes – atom-thin rolls of carbon that, despite their microscopic stature, are incredibly strong. They embedded tiny "forests" of carbon nanotubes within a glue-like polymer matrix and then pressed the matrix between layers of carbon fiber composites. The nanotubes, resembling tiny, vertically aligned stitches, worked themselves within the crevices of each composite layer, serving as a scaffold to hold the layers together.In experiments to test the material's strength, the team found that, compared with existing composite materials, the stitched composites were 30 percent stronger, withstanding greater forces before breaking apart.Roberto Guzman, who led the work as an MIT postdoc in the Department of Aeronautics and Astronautics (AeroAstro), says the improvement may lead to stronger, lighter airplane parts – particularly those that require nails or bolts, which can crack conventional composites."More work needs to be done, but we are really positive that this will lead to stronger, lighter planes," says Guzman, who is now a researcher at the IMDEA Materials Institute in Spain. "That means a lot of fuel saved, which is great for the environment and for our pockets."

Posted in: News, Aviation

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New System Allows Buildings to 'Sense' Internal Damage

Researchers at the Massachusetts Institute of Technology have developed a computational model that makes sense of the ambient vibrations that travel up a structure as trucks and other forces rumble by. By picking out specific features in the noise that give indications of a building’s stability, the model may be used to continuously monitor a building for signs of damage or mechanical stress.

Posted in: News, Data Acquisition, Detectors, Sensors

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Can algorithms create a pop-music hit?

This week's Question: Sony Computer Science Laboratory (CSL) in Paris is developing a system of algorithms which can create songs that cater to the user's taste, based on styles adapted from existing music. Starting with a sheet-music database of more than 13,000 existing songs, users choose several titles with the sound or feel that they would like the new song to incorporate.

Posted in: Question of the Week, Software

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‘Robomussels’ Monitor Climate Change

Northeastern University scientist Brian Helmuth and other researchers have developed "robomussels" that monitor climate change. The tiny devices have miniature built-in sensor that track temperatures inside the mussel beds.

Posted in: News, Machinery & Automation, Robotics

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Entry-Level PXI/PXIe Platforms

ADLINK Technology (San Jose, CA) announced new entry-level PXI and PXI Express (PXIe) platforms for PXI testing system startup users. PXES-2301 is an all-hybrid, 6-slot compact PXIe chassis with system bandwidth up to 8 GB/s. PXIe-3935 and PXI-3930 are embedded controllers with Intel® Celeron® 2000E 2.2GHz processors, delivering up to 50% increase in computing power and as much as eight times the bandwidth of available market offerings. ADLINK's PXIe-3935 and PXI-3930 significantly reduce maintenance burdens with easily replaceable battery and upgradable storage and SODIMM modules. Backup BIOS also eases recovery in the event of a main BIOS crash.Click here to learn more

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Scientists Find Twisting 3-D Electron Raceway in Nanoscale Crystal Slices

A scanning electron microscope image shows triangular (red) and rectangular (blue) samples of a semimetal crystal known as cadmium arsenide. The rectangular sample is about 0.8 microns (thousandths of a millimeter) thick, 3.2 microns tall and 5 microns long. The design of the triangular samples proved useful in mapping out the strange electron orbits exhibited by this material when exposed to a magnetic field. (Credit: Nature, 10.1038/nature18276) Researchers have created an exotic 3-D racetrack for electrons in ultrathin slices of a nanomaterial they fabricated at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). The international team of scientists from Berkeley Lab, UC Berkeley, and Germany observed, for the first time, a unique behavior in which electrons rotate around one surface, then through the bulk of the material to its opposite surface and back.

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