As published in:
High Performance Composites, September 2006
Engineered to Innovate-Composite Cores Evolve to Meet New Challenges
By Ginger Gardiner, Contributing Write, Ray Publishing

WebCore Technologies (Miamisburg, Ohio) manufactures the TYCOR_® family of fiber reinforced foam cores. Their proprietary process places fiber reinforcement through the thickness of closed cell foam sheets to form a corrugated or vertical truss-type structure, which is then infused with epoxy or other resin to produce a very robust and damage-tolerant core material.

WebCore is enabling the first all-composite fan case made with sandwich construction, which promises more than a fifty percent weight reduction versus current metal designs for the next generation of jet engines. Solid laminate composites are used for engine fan cases in smaller aircraft, with typically braided reinforcements. The GE-NX engine, which has been selected for Boeing's new 787 aircraft, will be the first large engine to use an all-composite fan case, but it will be very thick solid laminate construction.

WebCore began working with GE Aircraft Engines (Cincinnati, Ohio) in 2002 to develop a composite sandwich fan case that would be lightweight versus traditional aluminum and titanium designs, which can weigh over 1200 lbs (544 kg) for the 10-foot diameter and 4-foot long structures used in the newest GE90 and GENX engines. WebCore has proceeded through multiple Department of Defense Small Business Innovation Research (SBIR) programs, funded by NASA and the U.S. Air Force, to demonstrate building such a large composite sandwich fan case and scale-up of manufacturing. It has finished all of the extensive design work, built three manufacturing demonstrations and completed several rounds of testing.

The fan case of a jet engine is hidden from sight, located just outside the turbine blades and supports a containment ring. It is a stiffness-critical application, with two design approaches, based on how the structure will handle the case of an engine losing one or more turbine blades. The soft wall design allows turbine blades to go through the fan case wall, relying on a ballistic KEVLAR containment ring to act as a catcher's mitt. However, the fan case structure must maintain sufficient integrity after blade impact to enable the aircraft to land. The hard wall design does not include a catcher's mitt, and thus, the fan case structure must contain any thrown blades without catastrophic failure. This is a heavier approach versus the soft wall design, plus there is significant bulging in the fan case wall after blade impact. Thus, WebCore opted for a soft wall design, utilizing a KEVLAR wrap.

Rob Banerjee further describes the WebCore design, "We're using a combination of TYCOR and stitched skins. The carbon/epoxy and PMI foam TYCOR provides very high stiffness and strength at lighter weight than honeycomb and the skin is stitched through the core for additional properties and toughness. After impact, you don't see any delaminations, just a clean, clear hole. This ability to prevent delaminations helps us to maintain the strength and stiffness that is required after an engine blade impact." WebCore built a machine to stitch a cylindrical dry perform, but they can also simply stitch a flat panel and then form it. Impact testing at NASA's Glenn Research Center has consisted of high-speed photography recording a titanium blade projected from a ballistic gun at 500 to 1,000 ft/s through the fan case test panel. WebCore's sandwich fan case has passed all tests, and is now undergoing post-impact stiffness characterization, where the fan case is loaded and NASA measures the resulting deflections.

Banerjee projects that this technology will go into production by 2010 to 2012, which is the timing of the next large engines in development. "We are taking the slow and steady approach," he explains. "Our technology matches the strength and stiffness of current designs while offering the maximum in weight savings - more than a fifty percent reduction versus metal - and at NO COST INCREASE, well within the cost target for metal fan case products." Banerjee adds that WebCore is currently working with engine manufacturers on the large commercial aircraft fan case and is also looking into designs for smaller business jets, where the fan case is only 3 to 4 feet in diameter. They can also embed a circuit into the fan case to provide structural monitoring so that operators can see if there has been a blade impact, and if so, where it occurred and how much damage resulted.

Download/View TYCOR Core for Aircraft Engine Fan Cases