High Resolution Digital Camera Strain Measurement
When you strap yourself into your seat before a long flight, you probably dread snoring seatmates and overpriced food more than the possibility of mechanical failure. Modern travel is safer than ever—planes and cars are not only certified for mechanical reliability and efficiency, but made from component pieces that themselves have been scrutinized for durability and dependability. This wasn’t always the case. In the 1960s, accidents occurred in which jet turbine engines flew apart, sending their blades ripping into aircraft cabins. In response, every engine built today must have a containment system to ensure that turbine blades can’t penetrate the engine envelope in the event of an equipment malfunction. Engine designs are vetted for safety and reliability, and every material used in their construction undergoes stringent testing to ensure it is resilient enough to withstand heavy use and high levels of strain under a wide range of conditions.
“To study a material,” says John Tyson, president of Pennsylvania-based Trilion Quality Systems, “you typically make a little dog bone, which is a small specimen of the material, then put that in a tensile testing machine and pull it apart.”
The split-Hopkinson bar method (SHB) is commonly used to test strain rates in metals such as steel, aluminum, and magnesium alloys. The SHB, which uses bars and strain gauges, is very reliable, but can only test materials in standard shapes and can’t be used on composites, ceramics, and other advanced non-metal materials. That was a problem for the Air Force, which is using more and more non-metal components in new-generation turbine engines and military weapons systems. They needed a whole new testing method. With support from the Air Force Small Business Innovation program, Tyson and his team reimagined all the possible ways there might be to measure high levels of strain in a wider range of materials. Their research led to a completely novel method: Instead of measuring strain mechanically, Trilion’s system measures strain optically using two ultra-high- speed cameras.
“We stereo-image the surface with two high-speed video cameras to get full-field strain of the entire specimen,” Tyson says. “Because we’re measuring strain right on the specimen, shape and material aren’t limiting factors.” This optical measurement system not only overcomes many of the limitations of traditional strain measurement, it also provides a clear graphic representation of strain patterns, enabling a more detailed understanding.
Trilion’s optical scanning methods are also significantly faster than the traditional bar-and-strain- gauge method. “Where a traditional test might take 60 to 100 seconds, we’re doing it 100 microseconds, six orders of magnitude faster.”
This method has proven so successful it’s now the industry standard for high strain measurement, Tyson says. The system is particularly well suited for holistic full-field 3D deformation and strain measurement in the automotive, microelectronics, biomechanics, and aerospace industries.
The impetus behind the original SBIR was research and development of specialized ordnance that would minimize collateral damage, but the Trilion innovation was quickly generalized and adapted to a much broader range of applications. NASA is using the optical scanning system for strain testing advanced composite materials in and around jet engines and spacecraft, and civilian clients like GE, Boeing, and Lockheed are also now using the technology. On the ground, Trilion’s high-speed strain measurement system is finding good use in the area of automotive safety. “We do a lot of work on auto crashes,” Tyson notes, “looking at every side, from the vehicle materials to human biomechanics—bones, tendons, muscles, and that kind of thing.”
Tyson credits the SBIR program with not only allowing Trilion to perfect its technology for military uses, but for providing the resources they needed to commercialize their product for a wider market.
“One of the things that works well for us with the SBIR program is that we work really hard at commercializing what we’ve developed,” he said—no less than a revolutionary breakthrough in materials science.
“I think we’re exactly what the Air Force and Congress created the SBIR program for—a small business that develops advanced technology and then commercializes it, turning the technology into real products that both help the government and industry and contribute to public safety. We do a lot of really cool stuff, and thanks to the Air Force for funding it.”
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