Students at Worcester Polytechnic Institute (WPI, Worcester, MA) have been measuring the surface of a highly abrasive material to create a kind of topographic map. The work, being undertaken at the Department of Mechanical Engineering’s surface metrology laboratory, is part of an effort to develop the deepest understanding yet of how abrasive materials work.
According to Professor Christopher Brown, who has more than 25 years of experience working in surface metrology in the United States and Europe, he leads the only academic laboratory in the United States dedicated to advancing the understanding of the formation, behavior, measurement and analysis of surface roughness.
“All kinds of things happen at the surface,” says Brown, “such as heat transfer, scattering, osmosis and interactions with outside forces. Characterizing the surface to find correlations in these kinds of phenomena is essential to building a deeper understanding of what happens during the interactions between substances.”
Brown has forged a relationship with the industrial microscope unit of Olympus Scientific Equipment Group (Center Valley, PA), which provides industrial microscopes and other metrology and imaging instruments to laboratories across the United States and Canada.
Olympus has installed the LEXT OLS3100 confocal microscope in the laboratory. The microscope has 0.12-micron resolution and accurate 3-D measurement capability. With the system, Brown and his group are able to use brightfield, darkfield and differential interference contrast (DIC) microscopy techniques in both video and laser confocal imaging modes. The new confocal laser DIC mode is especially useful for highlighting subtle textural variations during surface analysis.
One project going on now is designed to help Brown and his colleagues better understand how abrasive media work in the grinding process. Abrasive media like alumina and diamond are complex, hard substances held together in a matrix, and understanding how to correlate abrasive geometry with the surface it creates is a major challenge. The LEXT system is being used extensively to do measurements and report a kind of topographic map that is analyzed via online software.
“Surface texture, roughness and geometry on a fine scale tend to be chaotic, and surface area tends to be deceptive. So studying it is essential,” Brown says. “There is an old joke that if you could flatten out the state of Vermont, it would be the size of Texas. We tried this virtually with GIS data and our area-scale algorithm and, sadly, Vermont doesn’t get quite that big. But the old joke does make the point that there is more area available on a rougher surface, and that extra surface area vastly influences performance.”
Before Brown had the LEXT system, making surface measurements of specific phenomena sometimes took hours or days of complex setup. But with the instrument, he is able to have two freshmen doing measurements, along with other undergraduate and graduate students, who are able to operate the equipment with ease.
Brown and his students use the system and provide feedback on its performance to Olympus. They also are planning to publish research papers that include work done on the equipment, and are open to visitors from other laboratories. “It has been a terrific kind of teamwork,” says Brown. “Olympus has been supportive and extremely knowledgeable in supporting our work.”
Olympus Scientific Equipment Group – Industrial Microscopes