Held Sept. 25-26 in Seattle’s Washington State Convention Center, CompositesWorld’s High-Performance Composites for Aircraft Interiors conference included some pretty frank discussions about the aircraft interiors market and the potential for composites to build its market share in this highly competitive and complicated arena. Cochaired by David Leach, composites market manager, Henkel Aerospace (Bay Point, Calif.), and Dan Slaton, associate technical fellow, Boeing Commercial Airplanes, Flammability and Airworthiness (Seattle, Wash.), the event was kicked off by composites market analyst Chris Red (Composites Forecasts and Consulting LLC, Mesa, Ariz.), who presented an outlook for composite materials and manufacturing in commercial transport interiors.
Interiors market: The inside story
Red pointed out that for composite materials and manufacturing processes, aircraft interiors actually represent a larger market (by volume) than airframe structures. Interior components account for as much as 40 percent of the commercial airliner’s empty operating weight. He assured attendees that there is room for composites to penetrate further. Red broke the interiors market into two distinctly different segments: the OEM-driven new-build market and the much more volatile — and two to three times larger — aftermarket. The new-build market, says Red, currently represents about 6 million lb (27.22 metric tonnes) of composite components annually. “By the time the [Airbus] A350 and [Bombardier] CSeries … and other new single-aisle aircraft enter production,” he reported, “the OEM market is expected to grow at least 50 percent compared to this year.”
The aftermarket potential, driven by replacement cycles and economic conditions, is more difficult to calculate. Generally, passenger seating is replaced every one to two years. Paneling, class dividers and other major components are turned over every four years. Complete cabin refurbishments take place every six to eight years. “Given the tough fiscal environment, the tendency has been to push these time frames as long as possible,” said Red of the period since the 2008 economic downturn. “However, in the past five fiscal quarters,” he observed, “latent demand has caused a dramatic upswing in activity.”
“Seats represent one of the biggest near-term opportunities,” Red contended, adding that new and replacement seating has the potential to consume 4 million to 5 million lb (1,814 to 2,268 metric tonnes) of composites within the next five years. “Switching to composite seats can save in the neighborhood of 400 to 450 kg [882 to 992 lb] on a single-aisle aircraft.” According to Red, there is a potential new-build and replacement market of more than 2 million coach seats per year.
Other potential areas for composites growth include brackets, trays and clips, cockpit flooring and seat rails. “Combined, the existing suite of composite applications plus some of these new opportunities indicate that composite materials will make up perhaps as much as 40 percent of the total tonnage of interiors components, going forward.”
Although phenolic resins — the current resin system of choice for interiors applications — will continue strong in the future, Red believes thermoplastics will play a significant role in displacing metals in new aircraft cabins and might also begin to displace phenolics in some composite applications.
Further, more carbon fiber-reinforced polymer (CFRP) is earning its way into the cabin, he said. And there is a growing interest in recycled carbon fiber for applications such as seat backs and trays. “I believe that as we move through the next decade, there will be thousands of tons of [reclaimed carbon fiber] sent to recycling,” said Red, “and there is a great interest in returning this to the cabin.”
Hot topic: Fire safety
Not surprisingly, material flammability was a burning issue throughout the conference. There was much discussion of certification standards and test methods. An abundance of new materials and coatings were announced, designed specifically to meet the stringent flame, smoke and toxicity (FST) requirements for aircraft interiors applications.
Robert Ochs, project engineer, FAA Technical Center (FAATC, Atlantic City, N.J.), updated attendees on the Federal Aviation Admin.’s (FAA) ongoing fire safety research projects. Special mention was made of the agency’s proposal to update, reorganize and improve safety requirements for materials flammability, a move that would shift requirements to a more threat-based approach. Ochs stressed that in-flight fires in inaccessible areas are the most dangerous. Large-scale testing at the FAATC indicated that previous test methods permitted the use of materials that, in practice, perform very poorly. “Mitigation of flame spread is the most effective means of preventing catastrophe,” he said, noting that updated and more stringent test methods have been mandated for insulation and are in progress for ducts and wire insulation.
Boeing’s Slaton called attention to new flammability test methods for composites aimed at flame propagation and described research that evaluated common materials used in inaccessible areas by using three different test methods: foam block, radiant panel and Méker burner. The Méker (or “meeker”) burner, named for its inventor, French chemist Georges Méker, is similar to a Bunsen burner but has a wider and hotter flame. Slaton said it shows potential for use in a more stringent test method and could help provide a simpler test for aircraft certification, although further testing is necessary.
Scott Campbell, director of flammability engineering, and Panade Sattayatam, engineering manager, both at C&D Zodiac (Huntington Beach, Calif.), and Michael Jensen, manager, Composites and Adhesives at Boeing, teamed up to present an update on the Flammability Standardization Task Group (FSTG), a subgroup of the FAA’s International Aircraft Fire Test Working Group, which was formed to collaborate and propose industry-wide standard methods of compliance. FAA flammability requirements and compliance methods were interpreted differently by regional FAA organizations, other regulatory agencies and industry suppliers and manufacturers Jensen explained. A primary goal of the effort, then, is to address some of these inconsistencies and provide greater test standardization.
Task group members have studied substrates, adhesives/syntactics, textures, laminate colors and paints in an effort to determine which flammability tests, and combinations thereof, will yield the most accurate and repeatable results. Although new types of cores, prepregs, adhesives, panel inserts and so forth will still require testing, Jensen says these methods can streamline the overall testing process.
Jensen stressed that industry collaboration in the development of testing methods was critical to making “our industry more competitive,” and he urged attendees to use the collaborative methodology developed for the FSTG team, which consists of 80 companies and more than 200 individuals, for areas outside of flammability.
A conference highlight was associate professor Jaime Grunlan’s presentation on research into a flame-retardant nanocoating at Texas A&M University’s Polymer NanoComposites Lab (College Station, Texas). Rather than mixing the fire-retarding (FR) nanoclay filler into the bulk polymer — a typical strategy — Grunlan’s approach puts the clay at the part surface in an ultrathin coating. The water-based nanocoating is applied layer by layer (at a rate of 5 seconds per layer) via a positively charged spray or dip process.
Grunlan reviewed tests conducted using polyurethane (PU) foam and cotton fabric. For PU foam tests, 1 percent anionic montmorillonite (MMT) clay and 0.1 percent cationic chitosan (which comes from exoskeletons of crustaceans) were deposited on open-cell PU foam by alternately dipping it in diluted aqueous mixtures that contained each ingredient. Reportedly, a “nano brick wall” was created after 10 clay/polymer layers had been deposited. After 10 seconds of exposure to a direct flame from a propane torch, only the coating’s outermost surface was charred. No flame was observed after 22 seconds of exposure, and white flexible foam was revealed under the protective char layer when the exposed foam was cut open.
“It’s 3-D coating every individual fiber, and you don’t even know it’s there,” Grunlan claimed. The coating reportedly provides a heat shield and gas barrier simultaneously and can eliminate melt dripping in foam and ignition in cotton fabric. Grunlan’s group has not yet found a substrate that can’t be coated using this process.
Several presentations focused on the development and application of other new FR materials systems. Carl Varnerin, VP, research and development, Barrday Advanced Materials Solutions (Cambridge, Ontario, Canada), discussed the fire resistance and adhesive properties of his company’s phenolic- and epoxy-based prepregs. Varnerin believes there is a need for “more flexibility in decorative materials, particularly for single-ply, thin-core constructions, which call for even lower OSU heat-release systems.” He also contended that snap-cure, self-adhesive, fire resistant composite systems — phenolic and epoxy — could add value and increase throughput. At 135°C/275°F, the company’s new snap-cure EP2052 epoxy prepreg reportedly cures in 20 minutes in a press molding operation. The prepreg is self-adhesive to aramid and aluminum honeycomb.
Barrday also conducted tests on flame-retardant packages for its LC194 and LC196 phenolic prepregs in an effort to significantly reduce the peak and total OSU heat-release performance, while maintaining FST performance and good mechanical performance in terms of its adhesion to honeycomb. This resulted in the company’s new LC294 toughened phenolic resin system, available in press and vacuum-bag grades, as well as LC296, a crushed-core grade. Both systems reportedly are viable candidates for interior applications that require prepregs that make a very low contribution to OSU heat release peak and totals. LC296 has also demonstrated a capacity for rapid cure.
Rick Pauer, market manager, CCP Composites (North Kansas City, Mo.), highlighted his company’s intumescent FireBlock flame-retardant fiber-reinforced polymer. “Intumescent materials work by forming a char layer at the interface of the fire source and the composite laminate, thus cutting off the oxygen accelerant from the organic fuel source,” explained Pauer. CCP has developed aeronautic grades of its FireBlock system that meet Federal Aviation Regulations (FAR) 25.853a using its halogen-free Norsodyne polyester resin systems (H81270 TF and H81370 TF) combined with its FireBlock 2330PAWK745 unpromoted flame retardant gel coat (<1.44 specific gravity). The gel coat is also available independently for use as an in-mold coating.
On the adhesive front, Dr. Patrick Zimmerman, lead senior application specialist, 3M Aerospace & Aircraft Maintenance Dept. (St. Paul, Minn.), discussed the company’s pumpable, low-density FR void fillers and adhesives for aircraft interiors. For both the low-density edge and void fillers and the semistructural and structural adhesives, two fire-resistant families have been developed.
Les Fox, senior scientist at Henkel, detailed the company’s two new FR products for interior applications. Loctite LP31201.0 FR is a one-part, low-density, high-compressive-strength potting compound. Loctite EA9364 FR, a two-part, extrudable paste adhesive, is available in side-by-side cartridges. Both products are free of halogen, antimony and phenol. “Whenever you try to make a product fire retardant, you almost always give up another property,” commented Fox, stressing the difficult process of developing a viable FR product. Henkel’s new products are self-extinguishing, meaning they won’t support combustion — an important characteristic for a product that might be inaccessible when in use.
Focus on foam-filled honeycomb
Attracting a lot of interest was GillFISTS (foamed in-situ thermosetting system). Described as a “novel means of filling honeycomb core with foam” by Matt Lowry, director of R&D, M.C. Gill (El Monte, Calif.), the system features a liquid coating applied by a curtain-coating apparatus to ensure that it uniformly coats the honeycomb’s cell surfaces. During a subsequent thermal process (standard to processing), the coating foams and fills the cells. The foam density is controlled by the application process and can range from 0.31 lb/ft3 to 10 lb/ft3. In answer to a question about controlling the process, Lowry explained that for an 18-inch/457-mm thick honeycomb with a 1.3 lb/ft3 foam density, the variation in density throughout the core was ±10 percent. The cell size, which ranges from 0.125 to 0.375 inch (3.17 to 9.52 mm), is reportedly self-regulating.
Based on phenolic resin chemistry, the foam begins to expand at 250°F/121°C. The foam can be pre-expanded for use in applications such as VARTM, where the goal is to stop resin from invading the honeycomb cells during infusion. But the coated honeycomb also can be dried at 200°F/93°C and stored for thermal foam-fill processing at a later date.
GillFISTS-filled honeycomb is suitable for thermal insulation and acoustic damping, said Lowry. The ability to control foam density in the honeycomb reportedly enables customers to “tune” a sandwich panel’s acoustic properties, which could make them suitable for aircraft interior sidewall applications.
According to Lowry, impact tests show that damage doesn’t propagate throughout the GillFISTS-applied foam. Although the honeycomb’s mechanical properties are unaffected by the GillFISTS process, it does reduce the product’s fire retardancy, but Lowry pointed out that it is still well within an acceptable range.
Innovation in carbon
Another attention-grabber was Hexcel’s (Stamford, Conn.) HexMC, a quasi-isotropic molding compound for structural aerospace applications. Designed to bridge the gap between low-performance, low-cost sheet molding compound (SMC) and high-performance, high-cost autoclaved prepreg, the material begins with an aerospace-grade unidirectional (UD) prepreg precursor (8552 resin system/38 percent RC and AS4 carbon fibers/150 g/m2) that is slit, chopped and randomly redistributed to make approximately 2-mm/0.079-inch thick, 200 g/m2 mat, available in 450-mm/17.7-inch wide rolls.
Said to be extremely damage tolerant, HexMC can be molded into a variety of geometries, reported Bruno Boursier, Hexcel’s R&T manager. Attainable shapes include sharp angles, deep draws, box corners, curves and gussets. Tension, compression and flexure moduli are 90-plus percent that of quasi-isotropic UD tapes. The trade-off comes in the in-plane strength, which drops to 50 percent of the original strength.
Hexcel has developed proprietary mold designs and processes that it says will preserve the transverse isotropy of the HexMC material in critical areas of parts and ensure minimum fiber distortion. Currently a special epoxy formulation is used for parts that need to comply with FST requirements (but not heat-release requirements) of FAR 25. A structural thermoset formulation that will meet FAR 25 OSU requirements (65/65 heat release) can be produced, but it will not perform as well for OSU as thermoplastics, explained Boursier, who sees OSU as the factor that currently limits HexMC use in interior applications.
Also of interest was a presentation on recycled carbon fiber given by Jim Stike, CEO, Materials Innovation Technologies-RCF (MIT-RCF, Lake City, S.C.). To date, MIT-RCF says it has reclaimed 1.5 million lb (680.4 metric tonnes) of carbon fiber scrap from landfills, not to mention the material that comes directly from manufacturers. A test barrel for Boeing’s 787 program, for example, was chopped up and recycled, and bicycle manufacturer Trek (Waterloo, Wis.) has implemented a recycling program for its carbon bike frames that has, thus far, amassed 140,000 lb (63.5 metric tonnes) of scrap.
Reportedly, the pedigree of the incoming material is very important. Reconditioned material can be supplied as chopped fiber (either fully recycled fiber or blended with virgin fiber) and fed into the company’s 3-DEP system to make preforms, or it can be used in its new compression molded co-DEP rolled goods line to make nonwoven mat. (For more on carbon fiber recycling, see ““Carbon fiber reclamation: Going commercial,” under "Editor's Picks," at top right.)
Opportunities for thermoplastics
SABIC (Pittsfield, Mass.) product development engineer Mohammad Moniruzzaman discussed high-flow, high-strength, OSU-compliant carbon fiber-filled Ultem compounds. Ultem resins are a family of amorphous thermoplastic polyetherimide (PEI) resins with elevated heat resistance. Reportedly, the company’s EX008PXQ compound (40 percent carbon fiber, PEI and proprietary additives) is 50 percent lighter than aluminum, stronger than die-cast aluminum and offers similar specific modulus and specific strength as machined aluminum (see “Carbon fiber food tray arm: Better and cheaper,” under Editor's Picks").
Tim Greene, global product manager at Greene, Tweed & Co. (Kulpsville, Pa.), discussed carbon fiber-reinforced thermoplastics for metal replacement in challenging aircraft interior components. There’s a “lack of cost-effective, complex-shaped composite solutions,” said Greene. The company has developed discontinuous fiber composites intended to bridge the gap between continuous fiber composites that offer superior performance but limit part complexity and injection-molded composites that can reproduce complex detail but are semistructural. In the process, aerospace-grade carbon fiber-reinforced UD prepreg tape (thermoset or thermoplastic matrix) is processed into random “chips.” Finished parts are matched-die compression molded. The resulting part reproduces complex 3-D geometry with high fiber content. Unlike with injection molding, the fiber length (0.5 to 2 inches/12.7 mm to 50.8 mm) is preserved.
The company’s Xycomp DLF offers discontinuous long fiber and a thermoplastic matrix. Greene stressed that the material is intended not to displace thermoset composites, but rather to replace metals in complex multipiece assemblies. “We’re looking at all the bits and pieces of metal that remain on the aircraft,” he said. Xycomp Carbon/PEEK DLF, which offers between 35 and 50 percent weight savings compared to metal, has been certified for and is currently flying on Boeing 787s.
During a subsequent group discussion, Greene stressed his belief that thermoplastics and thermosets belong inside the aircraft. “There’s a place for both, and I think the key is for us as an industry to understand where each fits,” he said.
Focus on applications
Redesigning aircraft seating to reduce weight and optimize capacity has become a priority. Bob Yancey, senior director, Global Aerospace and Marine, Altair Engineering Inc. (Troy, Mich.), highlighted his company’s efforts on this front. “Every engineer can tell you where you need weight and strength, but they can’t always tell you where you don’t need it, and that’s where you’re going to save weight,” explained Yancey. His team uses topology optimization software to define the nondesignable spaces, such as attachment points, and the designable spaces in between. Then the team considers applied loads and boundary conditions and determines the optimal structure. One result is a better understanding of where the main load paths are, which also enables better control of fiber orientation, he explained.
A high-concept seat design was presented by Christine Ludeke, principal, ludekedesign (Zurich, Switzerland). Based on the idea of “active seating,” the seat is constructed using a trademarked aerasknit cover on a carbon fiber back shell. The recline is built into the fabric, eliminating the need for a mechanical recline mechanism. The seat concept is still in the development phase.
Patrick Phillips, director of business development, Norduyn (Montreal, Quebec, Canada), showed off the company’s new lightweight Quantum galley cart by easily lifting it up onto the speaker podium. The cart has a carbon fiber single-body shell produced using vacuum-assisted resin infusion. A primary manufacturing challenge was to produce the straight sides without bowing, which was overcome via fiber manipulation during processing.
The testing was extreme, explained Phillips. The cart withstood 900 lb/408 kg of pull on the front door, 5,000 cycles of impact on the side panels and door, scratch tests and an impact test that applied 90 units of impact force to its door. Although aluminum doors typically bend under this test, the composite door, which flexes, can be closed and used again, reported Phillips. Reportedly, the cart also offers improved thermal efficiency.
Currently, Norduyn has 4,000 carts in the air, with a reported backlog of 30,000 units. Phillips estimated that there are about 1 million carts in the world, explaining that one airplane can have 80 to 100 carts, with three to four sets on the ground in major airports. Airlines are currently going through an intensive replacement phase, he added.
Axel Braun, head of Gurit product development (Kassel, Germany), and Sajal Das, president and CEO, Novoset LLC (Peapack, N.J.), discussed the application of modified cyanate ester resins, such as Gurit’s PN900, in air duct applications. Braun reported that the phenol-formaldehyde-free, low-pressure cure, low-shrink systems are a viable solution that offers good surface quality in applications that do not require high-impact strength. In fact, PN900 with either an E-glass or a hybrid 50/50 glass/carbon reinforcement has been qualified at Boeing and Airbus and is in use in high-temperature ducting in current models. Braun showcased the low-pressure tube process used to manufacture an Airbus air duct. A monolithic laminate and sandwich structure was molded over a silicone inliner (pressure tube) on a rigid metal tool with two halves. The applied pressure was between 7 and 26 psi (0.05 and 0.18 MPa). The minimum curing time was 75 minutes at 275°F/135°C.
On a separate note, Bruno Croteau-Labouly, president, FDC Composites (Saint-Jean-sur-Richelieu, Quebec, Canada), was on hand to champion the use of VARTM in aircraft applications, which he believes offers good potential in aerospace. He believes the reluctance of certification authorities to accept infused parts as compliant is one roadblock, as are the challenges involved in infusing phenolics. According to Croteau-Labouly, FDC has invested a lot in the R&D of infused phenolics and has developed FST-compliant parts.
Think like an airline
In the featured panel discussion, Greene (from Greene, Tweed & Co.) questioned how important weight actually is to the interiors market. “One challenge we’re seeing as a components supplier … is that the aircraft manufacturer is willing to pay more value for weight savings than the interiors manufacturer that sells directly to the airlines,” he said. “Is there really a value placed on weight savings?”
“In day-to-day operation, weight is a variable, unlike it is on the structure where it is there forever,” responded Bill Archer, president and CEO of Landmark Aerospace (Kennesaw, Ga.). “So, it’s a factor, but it’s not as critical.”
Later, Archer encouraged everyone to “think like an airline” when trying to get their materials and products specified for interiors applications. The interiors market is a very complicated arena, fraught with complex certifications, demanding customers and contradictions, he explained. Airlines want innovation at low risk, lighter weight without sacrificing durability and high quality at low cost, he said. Speed to market is also critical. “Once a new product is announced, customers want it now, so a two- to four-year program is compressed as airlines push to get it done faster.”
Although the major airlines still face tough economic times, Archer stressed that “it’s a growing industry, and airlines are getting better at managing the peaks and valleys to maintain a profit.” The battleground is clearly in business class, he contended. “Getting the loyalty of a business-class customer is important,” he advised, “and there’s a lot of effort being put on this front. There’s been a lot of money spent on business class, and there’s going to be a lot more spent in this area.” And while expectations are lower on a low-cost airline or in a low-cost seat, business class comes with greater expectations of quality. The future, he predicted, will be impossible without composites.