Facts and Friction
From camshafts to pistons to ball bearings, something is always rubbing something else — often the wrong way. Farshid Sadeghi, recently named Cummins Professor of Mechanical Engineering, faces friction on a daily basis as the director of the Mechanical Engineering Tribology Laboratory (METL), and it sparks his creativity.
Camera Ready: Professor Farshid Sadeghi tweaks the instruments in his MEMS research.
“One of the issues we are working on is to try and measure friction,” Sadeghi says. “It’s a very difficult parameter to determine.”
Sadeghi brings an innovative approach to traditional tribology through his work with micro-electrical-mechanical sensors (MEMS). Sadeghi uses remote MEM sensors to measure temperature — the byproduct of friction. Where there is friction, there is heat.
This indirect method for quantifying friction is especially interesting to manufacturers of bearings, who want to analyze the ball-cage temperature and impact forces. Sadeghi and his METL researchers are able to learn about bearing performance by measuring how hot the cage gets. Because they can’t attach wires to the cage, they have developed a wireless sensor.
“The cage is significantly higher in temperature than the surroundings,” Sadeghi says, corroborating the analytical work carried out by industry researchers. His inventive and elegant approach has caught the attention of governmental and aeronautical groups at the Department of Defense, the Naval Air Systems Command, Raytheon, and Rolls-Royce, and this summer he presented his findings at meetings in Germany and the Netherlands.
MEMS sensors have been proposed to be used on satellites as well, where two bearings support a “flywheel” that stabilizes the satellite’s orbit. When the bearings go bad, the satellite wobbles out of orbit. The MEMS sensors can detect temperature changes indicative of trouble before the bearings fail. With this warning, a second “backup” flywheel, also referred to as an attitude control wheel, can be brought online, and the vulnerable one can be disabled gradually.
Soon Marine helicopters will be equipped with MEMS sensors in their tail rotors. The shaft of the rotor is supported by a number of bearings that are replaced on a routine maintenance schedule, whether they need replacing or not. This represents a significant cost — tens of millions of dollars per year according to Sadeghi. He has developed a test procedure to predict bearing failure, where again, a temperature increase signals an anomaly.
“Hopefully this technology will provide the details they require to replace bearings on a need rather than a time basis,” Sadeghi says.
Beyond the MEMS sensors, Sadeghi is also excited about new research in the realm of rolling contact fatigue, a factor always considered with any kind of rotating machinery. He has begun to look at materials’ microstructure — the “topology” of materials’ grains.
“If fatigue occurs on the microscopic level, why not look at the micron-level geometry and see what is happening?” Sadeghi asks. “Is there any correlation between that level and the rolling contact fatigue?”
The answer seems to be yes. “One of the amazing things is that the results we have obtained are in such close agreement with experimental results by other parties,” Sadeghi says.
Sadeghi says he is most excited about the interdisciplinary nature of tribology. Not restricted to just one area of mechanical engineering, tribology offers overlaps with disciplines like fluid and solid mechanics, heat transfer, and material science. “Together we build ideas, develop them, and try to make significant impacts.”