April_AMP_Digital

1 2 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 0 Previously, the NIST team added small molecules that fluoresce after the impact of mechanical force. These molecules, called “mechanophores,” change color or light up, helping iden- tify tiny nanometer-sized openings or cracks between the fiber and resin. The NIST team has expanded on their prior work to take this technology to the next level by incorporating the mechanophore throughout the com- posite resin. Their new approach allows scientists to use special microscopy imaging techniques to measure FRP damage. The approach incorporates a minute amount of a fluorescent dye called rhodamine that causes no appre- ciable changes in the material’s physi- cal properties. If the new mechanophore is em- bedded in structures made of FRP, field testing for fatigue could be done inexpensively and on a regular basis. Structures like wind turbines could frequently be scanned easily for inter- ior cracks, even years after they’ve been erected. TESTING | CHARACTERIZATION ANALYZING METALS AS THEY INTERACT Working together with researchers at the University of North Texas, Den- ton, a team at the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory, Aberdeen Proving Ground, Md., has developed a new approach to analyze the tribologi- cal response between steel and silicon nitride that takes place as the two met- als interact, rather than after the sam- ples have cooled off. This latest method of studying wear and tear may allow researchers to observe fleeting chemical reactions that occur at the contact site. The researchers conducted an ex- periment using a Ball on Disk tribome- ter that slid a rolling silicon nitride ball against a steel rotating disk that was heated to 120°C with a hot plate under- neath. This experiment represented the first known attempt to analyze the tribological response of steel and silicon nitride in the middle of a high-sliding speed test. The team discovered that the frictional heating induced a chemical reaction that left be- hind a lubricating thin film at the highly loaded contact zone. Using the new approach, the team managed to pinpoint the exact time that the chemical reaction occurred from obser- vations of the wear tracks’ color change during the experiment and also verified that a series of oxida- tion reactions had taken place. According to the researchers, this new in-situ approach to examining dry sliding mechanical contacts holds the potential to significantly improve the Army’s efforts to develop machinery that can better withstand high tempera- tures, loads, and speeds. arl.army.mil . NIST’S NEW TOOL TO MEASURE FRP DAMAGE Fiber reinforced polymers (FRPs) can be found in everything from aero- space and infrastructure to wind tur- bines. Monitoring the damage that occurs in these materials as they age is key to detecting early warning signs of failure. Now, a team at the National Institute of Standards and Technology (NIST), Gaithersburg, Md., has devel- oped a tool, integrated into these materials, to monitor these changes as they happen in order to develop more fatigue-resistant composites. Army researchers Stephen Berkebile (left) and Nikhil Murthy (right) examine how silicon nitride responds to steel during dry sliding mechanical contact. Courtesy of Vincent Coburn. NIST discovered how to more easily spot damage of the fiber reinforced polymers in wind turbines. MTS Systems Corporation, Eden Prairie, Minn., a leading global supplier of high performance test systems, motion simulators, and sensors, will work with Auburn University, Ala., to accelerate additive manufacturing research and test development. As part of the alliance agreement with the university, MTS will supply test equipment to Auburn’s National Center for Additive Manufacturing Excellence mechanical testing lab and share expertise to advance me- chanical testing methods for additively manufactured materials and components. mts.com, auburn.edu . BRIEF