3-D preformed composites: The leap into LEAP

The LEAP jet engine is the next generation of the successful CFM56 engine for narrow-body aircraft which powers more than half of the commercial aircraft ordered in the past decade. Produced by CFM International (Evry, France and Cincinnati, Ohio) — a 50/50 joint venture of Snecma and GE, formed in 1974.  Snecma/Safran (Paris, France) is responsible for the low-pressure fan sections and GE Aviation handles the high-pressure combustion core. LEAP reportedly will offer a 15 percent reduction in fuel consumption and CO₂ emissions, the lowest operating cost (thanks to less maintenance and longer intervals between service) and an aircraft departure reliability of 99.98 percent. The 3-D woven resin transfer molded (RTM) composites developed by Safran and AEC are a key enabling technology in LEAP’s ability to achieve this high performance (see Fig. 2).

      LEAP will use 18 carbon fiber-reinforced polymer (CFRP) blades that together weigh 168 lb/76 kg. The CFM56 has 36 titanium fan blades, totaling 330 lb/150 kg. Lighter composite blades produce less energy that must be absorbed in a blade-out situation, allowing a less massive containment system. Also, a less weighty fan disk can be used to hold the blades in place. The weight savings cascade through other structures for a total 1,000 lb/454 kg reduction per aircraft. The LEAP blade’s aero-acoustic 3-D swept geometry helps to reduce overall engine noise and to meet International Civil Aviation Organization’s (ICAO, Montréal, Québec, Canada) Chapter 5 noise regulations.

      Bird impact was a limiting design factor for the fan blade. A challenge for the 128-inch/3m diameter fan in the precedingGE90 engine, bird impact is magnified in the LEAP engine because on its smaller 78-inch/2m diameter fan — the first for single-aisle aircraft to use composites — the smaller blades offer less area to absorb the same impact energy.

      The 3-D woven preform developed by Snecma and Albany Engineered Composites (AEC, Rochester, N.H.) results in a composite blade without any inherently weak, unreinforced planes that could be susceptible to delamination failures — an advantage vs. laminates that feature traditional 2-D fabrics. As dictated by the design of the 3-D fiber architecture, “layers” in the blade are interconnected with fiber so that both the through-thickness and in-plane properties of the blade are fiber dominated. In various “zones” of the blade, there are different in-plane and out-of-plane loads experienced in service, and these zones each require unique 3-D woven architectures, tailored to meet their structural requirements.

      In addition to the blades, three other LEAP parts use AEC 3-D woven RTM composites: fan case, platforms and spacers. Platforms form the flow path between blades, while spacers are effectively springs that keep the blade in position while the engine is not spinning. 3-D woven technology is being evaluated for additional fan module components and also for ceramic-matrix composite (CMC) applications.

            Where fan cases have previously used a metallic ring with or without an aramid fiber over-wrap, the LEAP fan case — incorporating AEC’s contour weaving and 3-D preform technology — will be the first to integrate the containment into the case via a carbon fiber 3-D structure, eliminating separate manufacture, assembly and excess weight. The carbon fan case cuts weight 30 percent versus aluminum. The 3-D preform enables a shaped cross-section with an integral flange on each edge and meets stringent fan blade-out test requirements. 

This short article is a sidebar to a feature aritcle titled "Albany Engineered Composites: Weaving the future in 3-D." To read this artice, clikc on its title under "Editor's Picks," at top right.