8 A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A R C H 2 0 2 3 human-machine interface devices. Their new sensor consists of a silver nanowire network embedded in an elastic polymer. The polymer features a pattern of parallel cuts of a uniform depth, alternating from either side of the material—one cut from the left, followed by one from the right, followed by one from the left, and so on. The sensor gauges strain by measuring changes in electrical resistance. As the material stretches, resistance increases. The cuts in the surface of the sensor are perpendicular to the direction that it is stretched. This serves two purposes. First, the cuts allow the sensor to deform significantly. Because the cuts in the surface pull open, creating a TESTING | CHARACTERIZATION 3D IMAGING REVEALS CRACKING MECHANISM Solvingahalf-century-oldmystery, a research team from Japan’s National Institute for Materials Science identified the mechanism by which microscopic fatigue cracks grow in metals. The team found that these cracks grow along the slip planes of metallic crystals through 3D imaging of large-volume samples. Most cracks were found to be caused by a shearing force rather than the tensile forces previously thought to be responsible for the effect. The team re- cently developed an electron microscope-based analytical technique capable of high- resolution, three-dimensional crystallographic imaging of a large-volume metallic sample—100 times larger than the volume observable using conventional methods. This was the first time that fa- tigue cracks of approximately 200 µm in length were imaged three-dimensionally at high resolutions. This was achieved by applying the technique to a heat- resistant superalloy developed for use in aircraft engines. The team analyzed this image across the large sample and quantitatively determined the relationship between crack growth paths and crystalline orientations, leading to the discovery of a crack growth mechanism that differs from the mechanism conventionally assumed. www.nims. go.jp/eng. SENSITIVE STRAIN SENSORS A new, stretchable strain sensor was created by researchers at North Carolina State University, Raleigh, and features a unique combination of sensitivity and range, allowing it to detect even minor changes in strain with greater range of motion than previous technologies. The researchers demonstrated the sensor’s utility by creating new health monitoring and Triangular holes make this material more likely to crack from left to right. Courtesy of N.R. Brodnik et al./Phys. Rev. Lett. The new Vanta GX precious metal analyzer from Evident Corp., Waltham, Mass., offers a simple way to obtain the purity and composition of gold, jewelry, coins, and other pieces. Accurate and nondestructive, the countertop instrument uses x-ray fluorescence to determine precious metal content, karatage, and fineness in seconds so jewelers and others can see the purity of the gold, silver, platinum, palladium, and other precious metals in valuables. evidentscientific.com. With a new high purity testing center, cleaning specialist Ecoclean GmbH, Germany, is expanding its capacity for cleaning tests to suit high-tech components with extremely high purity requirements. The center features five cleaning systems for the technologies, media, and processes used in wet chemical component cleaning, such as ultrasound, injection flood washing, plasma cleaning, pulsed pressure cleaning, and ultrasound plus. ecoclean-group.net. BRIEFS A fatigue crack shown by a reconstructed morphology that adds an electron backscatter diffraction image from a cross section. Courtesy of National Institute for Materials Science. The patterned cuts in this elastic polymer, which houses the new sensor, enable a greater range of deformation without sacrificing sensitivity. Courtesy of NC State University/Shuang Wu.
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