1 0 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 | A P R I L 2 0 2 2 technique for detecting reduced efficiency in hydrogen fuel cells when enduring periods of excess or insufficient water. By using sensors that measure magnetic flux density, the amount of current generated can be monitored noninvasively, which can signal a problem. This work could lead to technology that can improve the reliability of fuel cells while also significantly reducing the carbon footprint of cars. The new detection system is based on the magnetic flux produced by electrical currents inside the fuel cell. When the system is operating correctly, its electrical currents generate a characteristic pattern of magnetic fields that can be detected by sensors. This allows failure states to be immediately registered after changes are noted in the magnetic flux. “Our research opens the possibility for automated control systems to be integrated into future fuel cells,” says lead researcher Yutaro Akimoto. This could pave the way for more efficient and practical zero-emission vehicles. www.tsukuba.ac.jp/en. SOUND MEASURES ELASTICITY Scientists from the U.K.’s University of Nottingham are measuring the speed of sound across a material’s surface todeterminemicroscopic elasticity. The innovation, referred to as spatially resolved acoustic spectroscopy (SRAS), uses high-frequency ultrasound to produce microscopic resolution images of the microstructure and maps the relationship between stresses and strains TESTING | CHARACTERIZATION FATIGUE CRACK MECHANISMS A team of researchers from Cornell University made advancements in better understanding how materials break. Using atomic modeling, the researchers identified the mechanism that causes fatigue cracks to grow—a defect in the structure that begins near the crack tip, moves away from it, then returns to a slightly different location. The finding could help engineers better anticipate a material’s behavior and design novel alloys that resist fatigue. The researchers set out to create a series of simulations of a structural alloy in a vacuum. Each simulation inserted a different artificial mechanism that might pro- voke the cracks to move forward, as they would in the real world. Some mechanisms included new sources of defects, irreversibility, and different forms of localized strain. Each time, the crack refused to budge. A fourth simulation succeeded in propagating the crack after the team realized the defects needed to interact more closely with the crack tip, such that the atomic bonds would break. While the modeling explains the mechanical mechanism at the root of fatigue cracks, there is still an open question about what role the environment plays in their growth. The group is now researching how dislocations can be steered to different locations and how loading can affect the process. This new understanding of prolonged fatigue can be applied to the design of materials, which has historically focused on how much loading a material can take before it fails. cornell.edu. FUEL CELL FAILURE Researchers from the University of Tsukuba, Japan, developed a new Magnetic Analysis Corp. (MAC), Elmsford, N.Y., acquired TacTic, a division of Laboratory Testing Inc. The purchase expands MAC’s line of NDT systems to include ultrasonic test systems that detect surface and subsurface defects in round tube, pipe, and bar. The systems enable metal producers to cost-effectively test small batches of material or frequent diameter size changes. mac-ndt.com. Ipsen, Cherry Valley, Ill., expanded its field service capabilities to include ultrasonic wall thickness testing for vacuum furnaces, which helps verify the integrity of the vacuum chamber and determine its remaining lifespan. The service is available anywhere in the U.S. on both Ipsen and non-Ipsen equipment. ipsenusa.com. BRIEFS This graphic shows the modeled atomic configuration at the tip of a fatigue crack that is on the verge of emitting dislocation defects. Courtesy of Cornell University. Ipsen vacuum chamber wall thickness testing.
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