Two students pose with the wings of a Predator drone, which are moving to the new Composite Aviation Safety Center to be prepared for testing.
San Diego, Calif., Sept. 11, 2012 - The University of California, San Diego, has become the home of a major facility dedicated to studying all aspects of full-scale composite material aircraft structures, located in the new Structural and Materials Engineering building.
The Composite Aviation Safety Center will allow engineers to design and manufacture test specimens representing aircraft parts made from composite materials— for example, fuselage sections, landing gear and wings. These specimens can be outfitted with embedded sensors to detect damage and monitor their structural integrity while being tested under various types of loading, for example simulating the impact of everything from hailstones to baggage loaders. Finally, the data provided by the tests and sensors will be used to build models to predict damage and provide insight and methodologies that enable engineers to develop improved designs. This cradle-to-grave approach is unique to the Jacobs School of Engineering at UC San Diego.
“What makes us unique is that we will be researching the entire product development process from design, to computational analysis with improved low-cost fabrication and full-scale testing, and failure analysis after testing,” said John Kosmatka, a professor of aerospace and structural engineering at the Jacobs School and one of the lead researchers for the new facility. “We are able to embed sensors into the structural components during fabrication to improve our understanding of critical features and monitor the deterioration of structural performance over their operational life. We have the capability to go from micro-scale composite material development to full-scale aircraft components.”
This kind of research is becoming increasingly important as aircraft manufacturers move away from aluminum alloy outer skins and toward composite materials to build their primary structural components. One major concern is that composites can undergo damage that’s not visible to the naked eye from the outside of the aircraft. In the airline industry, the first line of defense to detect damage resulting from a severe event, such as an impact, is a visual inspection, which might not be able to detect damage to an aircraft’s composite skin and internal structure.
A single hit is unlikely to have significant consequences as aircraft are required to withstand exceptional levels of damage and still be able to execute extreme maneuvers that would happen only once in the lifetime of the plane. But researchers are trying to understand how repeated impacts, wide-spread impacts, and other kinds of severe events and loading affect aircraft over their lifespan. They are working on better understanding the underlying phenomena and seeking to establish better ways to detect, predict and avoid damage. This ultimately leads to improvements to make structures lighter and safer.
Design and manufacturing
The carbon nanotubes can be seen in the resin matrix, bonding to the carbon fibers. This image was taken using a Scanning Electron Microscope in the Nano3 research facility, at the University of California, San Diego. The two large fibers seen in the image are the carbon fibers which are nearly 20 times smaller than the average diameter of a human hair. The smaller strands connecting the adjacent carbon fibers are the nanotubes which are approximately 50,000 times smaller than the average diameter of a human hair.
In Kosmatka’s lab, engineers are investigating how carbon nanotubes can significantly improve reinforcement of the resin matrix found in composite materials commonly used in the aerospace, defense, automotive and sporting goods industries. The ultimate goal, working closely with Professor Kenneth Vecchio from the NanoEngineering Department, is to develop better carbon nanotubes that can be incorporated in critically stressed regions of large aircraft components. This project, which is in its early stages, provides an example of the kinds of interdisciplinary research that can only take place in the Structural and Materials Engineering building, which houses nanoengineers, aerospace and structural engineers.
Meanwhile, engineers in the lab of Hyonny Kim, a professor of structural engineering at the Jacobs School, are building replicas of pieces of aircraft fuselage, made of the same composite materials used in the Boeing Dreamliner. The structures are made up of panels about 12 times thicker than an aluminum soda can. Students, both graduate and undergraduate, acquire a wealth of knowledge about how aircraft are manufactured in the process, Kim said.
Sensors and testing
Structures built in Kosmatka and Kim’s lab can then be outfitted with embedded sensors constructed in the lab of Mike Todd, also a professor of structural engineering at the Jacobs School. The sensors use ultrasonic waves to detect damage, from cracks, to voids, to corrosion. They function much like “structural radar:” just as ships use sonar to bounce acoustic energy off of potential targets, this technology bounces ultrasonic energy off of potential damage. Todd and his team have successfully used the sensors on bridges and aircraft components. They also have used optical fiber sensors, particularly in composite materials, where the sensors can be embedded inside the materials.
In addition to the embedded sensors, damage also can be detected by special instruments placed on the outside of the structures and developed by the lab of Professor Francesco Lanza Di Scalea, also from the Department of Structural Engineering. In Lanza Di Scalea’s lab, researchers are using ultrasonic waves to detect and quantify damage, both during and after testing, or after an actual event, such as a crash.
Finally, all the data collected during the tests will come back to Kosmatka’s lab, where he and structural engineering professor Joel Conte are developing sophisticated probabilistic-based computational models to predict the type and growth rate of damage in composite aircraft parts. These computational models, along with an extensive experimental database, are being developed to predict the remaining life of in-service aircraft components, as a result making it easier to schedule maintenance, or provide a critical warning to the flight crew.Once the structures have been outfitted with sensors and other instruments, they will be submitted to a wide range of tests. Researchers in Kim’s lab are building a 20-foot long gas-powered gun to simulate the impact of high-speed projectiles. Another, smaller gun is already in operation and is designed to simulate the impact of hailstones on composite materials. It shoots ice spheres of up to 61 millimeters (about 2.5 inches) in diameter at over 250 meters per second and can be seen in action here. Researchers also simulate impacts on aircraft from ground equipment, such as cargo and baggage loaders — a major source of damage for airplanes.
The researchers’ work is funded by various agencies, including the Federal Aviation Administration.
The lab of Professor Hyonny Kim simulated the impact of hail on composite materials used in modern jets. Researchers launched ice spheres of about 2.4 inches in diameter at 108 meters per second using a gas gun built for testing ice impacts on aircraft structures. Their target was a 12" by 24" composite panel made of the same composite material used in the Boeing Dreamliner. The panel is about 12 times thicker than an aluminum soda can (0.064 inches). The research was funded by the Federal Aviation Administration.
Test on a composite testing specimen built by students in Prof. Hyonny Kim's lab.