R&D Brief
Vol 5. Num. 11
| June 23, 2008
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Composites Lab layup room expands capabilities
Tucked away in a corner of the National Institute for Aviation Research’s Composites and Advanced Materials Lab exists the lab’s highly capable and rapidly-expanding layup room.
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Layup room manager Allison Crockett
teaches the wet layup method to engineers
participating in a composites short course.
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The layup room has existed for several years, and has recently experienced several modernizations and capability and procedure updates under the management of Allison Crockett, NIAR research engineer and program manager.
The layup room’s current workload is made up of about 30 percent from the aviation/composite manufacturing industry and 70 percent from government entities like the FAA and the NIAR-Industry-State (N-I-S) research program.
“That is quickly flipping, because we’re getting more and more companies wanting us to fabricate their qualification or equivalency panels, as they’re having a hard time getting people to do it in a timely manner,” Crockett said. “Every month we’re getting another industry request, it seems.”
Crockett credits that growth in part to several industry courses on composite materials that NIAR and Wichita State University’s College of Engineering have offered over the past four years. To augment lectures on a variety of topics related to composites manufacturing and testing, the classes have always included hands-on training in the layup room—and that’s the first time a lot of the industry professionals in the class even realized the room existed, Crockett said.
What they’ve discovered upon arrival is a “clean room” with a large walk-in freezer, the most current bagging materials available, a controlled environment, and vacuum lines throughout the room, to optimize space and time. The lab has two large lamination tables for performing hand layup of resin-impregnated fiber forms (prepreg).
Plies are laminated most commonly in an open (one-sided) mold; the plies are then consolidated and “debulked” using a vacuum bagging process with an air-impermeable plastic. The edges are sealed with sticky tape and vented. The air within the plies from lamination process is then removed using a calibrated vacuum port. Next, the panel is cured in NIAR’s 3-foot-by-5-foot research autoclave, which applies temperatures as high as 1000 degrees Fahrenheit and pressure up to 400 psi. Once the part is cooled, it is inspected visually and by NDI for defects and anomalies. Finally, it is cut in the Composites Lab machine shop to the desired specimen sizes for testing in NIAR’s Composites, Fatigue & Fracture and Structures Labs.
“Our panels have come out and they’ve passed C-scans very well, with very few voids,” Crockett said of a recent project. “They’ve undergone testing and the strengths are really high. That would be a byproduct of good panel fabrication.”
Other types of layup that the staff of four full-time employees and three part-time students does most often are vacuum-assisted resin transfer molding (VARTM) and wet layup. For VARTM, fiber preforms are impregnated with resin inside a closed mold with the assistance of a vacuum. For wet layup, fiber preforms are impregnated with resin by hand, using rollers or brushes.
“The wet layup is a messier process because during lamination you have to mix the resin part A and B together and then apply adequate amounts to the various layers of fibers placed in an open mold. A squeegee or paint brush with short bristles usually works best to spread the resin mix around wetting each layer of fiber,” Crockett said.
In large part, the wet layup process at NIAR is used to perform repairs on panels being tested in FAA programs like “Effect of Repair Procedures Applied to Composite Airframe Structures” and “Aging of Composite Aircraft Structures” or N-I-S programs such as “Repair of Composite Structures” and “Composite Bearing Allowables Baseline.”
“The wet layup is one of the most common repair methods used in the field today,” Crockett said.
By client request, NIAR’s layup room has also performed a few other types of layup, including resin transfer molding (RTM) and filament winding. In the filament winding process,a machine passes fiber material through a resin bath just before the material touches a cylindrical mandrel creating a tubular structure which is then oven-cured or autoclaved on the mandrel.
Crockett hopes to be able to perform more of these types of manufacturing processes as well as more of their “specialties” when the Composites Lab gets space at the new National Center for Aviation Training at Wichita’s Jabara Airport. The training center is scheduled for completion in the fall of 2010.
“The plan is to move the entire layup room out to Jabara, where we will to have more than 5,000 square feet of layup space, two large ovens, two large autoclaves, a Gerber cutter, a big walk-in freezer and an even more controlled environment with more air filtration,” Crockett said. “We’ll have the capability of laying up three times the number of panels and offering a lot more courses.”
