CompositesWorld’s High-Performance Composites for Aircraft Interiors (HPC4ACI) conference was back in Seattle, Wash., from Oct. 2-3, offering, for a second year, a window into the aircraft interiors market, with an expansive view of newly realized and potential composite applications. Cochaired by Bjorn Ballien, technical program manager, Henkel Aerospace (Bay Point, Calif.), and Michael P. Kuntz, associate technical fellow, composites and plastics, The Boeing Co. (Seattle, Wash.), the conference was, once again, kicked off by composites market analyst Chris Red (Composites Forecasts and Consulting LLC, Mesa, Ariz.), who presented a 10-year interiors market outlook. The focus was on enhancing operating costs and revenue generation with composites.
Interiors market: Every pound counts
Gone are the days of commercial aircraft designed for less than 70 passengers, reported Red. Both regional and long-haul airliner programs are targeting larger capacities. Most new regional and single-aisle models will target capacities between 90 and 130 passengers. Over the next 10 years, regional aircraft (turboprop and jet) volumes are expected to decline, while single-aisle aircraft that fly longer routes are expected to grow 35 percent and eventually represent 60 percent of all operating commercial aircraft.
The trend toward larger planes, however, has a downside. Red sees a significant upward trend in fuel costs per seat. Despite significant improvements in airframes, engines and lighter-weight interior components that have enabled airlines to improve fuel efficiency by 46 percent from 1990 to 2012, fuel costs, as a percentage of overall fleet operating costs, continue to rise. In fact, Red reports, “rising fuel prices have become the dominant cost factor for airline operations, accounting for one-third or more of operating costs.” By 2022, he suggests, fuel could make up 50 percent or more of fleet operating costs.
Red said fuel prices are anticipated to climb an additional 50 percent over the rest of the decade. After accounting for that fact and a wide range of other factors, he estimated that one less pound on a single-aisle aircraft could save from $150 to $450 per year, per aircraft. Assuming a 1 percent overall weight savings, the benefit multiplies significantly: a single-aisle aircraft could shed from 1,000 lb to 2,350 lb (453.6 kg to 1,066 kg) for an annual fuel cost savings of $240,000 to $1.6 million per year (see Fig. 1, at left).
The composite interiors market is fairly mature — glass fiber and carbon fiber composites have been used to reduce the weight of interior components for more than three decades. But Red claimed there is “still plenty of room for improving weight, durability, aesthetics and functionality.” Composites currently represent only 20 to 25 percent of the total interior weight, and it could increase to 30 to 40 percent within the next 10 years. “Success in emerging interiors applications could drive annual production volumes up an additional 60 percent towards the end of the forecast,” he added.
Red noted a general trend toward more use of carbon fiber-reinforced polymer (CFRP) and the addition of thermoplastics, and he said it is reasonable to expect reclaimed carbon fibers from airframe production to flow into the interiors market at increasing volumes over the next decade.
Moreover, the interiors aftermarket, which is three times the size of the OEM interiors market, is “really where composite materials have the opportunity to shine,” Red maintained. Fuel savings are a great incentive for owners of older in-service and larger commercial aircraft to reduce weight during their regularly scheduled retrofits and replacements of aircraft interiors.
“Composite manufacturers and their supply-chain partners will be able to help airlines remain cost-competitive,” Red concluded, even with thinning margins (the overall airline industry profit margin in 2012 was approximately 1.5 percent of sales).
Hot topic: Thermoplastics
Many in attendance, including conference cochair Ballien, agreed that if thermoplastic composites are going to make significant advances in aerospace, now is the time. “Aerospace OEMs used to ask us to focus on improving material chemistry, in terms of specific properties, improved strength, etc.,” recalled Ballien. “Now, however, they are focusing on ... longer shelf and pot life [and] there is definitely a push to look at alternative materials that offer the properties already achieved, but at a lower cost and faster manufacturing time.”
According to Mike Favaloro, business development manager, Cutting Dynamics Inc. (CDI, Avon, Ohio), thermoplastics are the key to achieving both. “The bottom line is cost,” said Favaloro. “Nine times out of 10, if an aluminum part is cheaper, the customer is going to go to aluminum, and that’s something that we all have to fight.” But he argued that “thermoplastics allow for more rapid, automated, lower cost processes with improved properties.” Among those properties are desirable flame, heat, chemical and solvent resistance and high toughness. And, unlike thermosets, thermoplastics can be reformed, recycled and welded.
CDI offers continuous compression molding of aerospace components, including profiles for interior aircraft brackets, such as C-channels, H-beams, I-beams and L- and T-stringers (see “Aerospace-grade compression molding,” under "Editor's Picks," at top right). To date, CDI has processed 24-inch/610-mm wide continuous laminates with a thickness up to 1 inch/25.4 mm into continuous shapes with a maximum size of 5 inches by 5 inches (127 mm by 127 mm).
Also on board is Triumph Composite Systems (TCS, Spokane, Wash.), which has converted many of its parts from vacuum-bagged layup to compression molding and, in turn, moved from thermosets to thermoplastics. TCS manufactures composite ducting, floor panels, and other interior components. Nick Busch, R&D engineer at TCS, described an example of such a conversion, which compared a vacuum bagged layup of four plies of glass-reinforced polyester resin vs. compression molding of four plies of trademarked Cetex glass-reinforced polyetherimide (PEI) from TenCate Advanced Composites (Morgan Hill, Calif.). By moving to thermoplastics, TCS saw, among other things, a reduction in part-to-part variation caused by mechanical processing methods. And, says Busch, “Overall, we saw a 50 percent reduction in part operations and a 75 percent reduction in cycle time with compression molding.” (Read more in "Compression molding mass out of aircraft interiors," under Editor's Picks.")
The extent to which thermoplastic composites have infiltrated aircraft programs was exemplified by David Manten, president, Dutch Thermoplastic Composites (DTC, Almere, The Netherlands). DTC specializes in press forming of fiber-reinforced thermoplastics and has developed low-cost, high-volume manufacturing technologies for them. For Toulouse, France-based Airbus, DTC manufactures thousands of thermoplastic composite clips and cleats that are used to hold the skin to the frame of the aircraft. In all, 1,500 parts (800 unique part numbers) are produced for each aircraft, for as many as 110 aircraft per year.
Long fiber adds strength
Ralph Maier, manager, aerospace technologies for BASF Corp. (Florham Park, N.J.), and Raj Mathur, VP and director, technology and business development, PlastiComp (Winona, Minn.), described collaborative development of long-fiber-reinforced polyethersulfone (PES)-based composites. PlastiComp manufactures unidirectional tapes and profiles and the trademarked Complet long-fiber-reinforced compounds that can be either glass or carbon fiber-reinforced with a range of matrices. Complet LCF-PESU is carbon-fiber reinforced and based on BASF’s flame, smoke and toxicity (FST)-compliant Ultrason E PESU. According to Mathur, the combination results in improved fiber/matrix adhesion and parts with high strength-to-weight ratios.
“We integrate manufacturing, design, and material development,” explained Mathur. “A lot of design options open up when these three areas are integrated.” PlastiComp, therefore, not only controls molding process parameters, gross fiber volume fraction, and fiber length and orientation, but also can optimize the fiber chemistry and morphology, he explains. Targeting continued replacement of metal components in aircraft interiors, PlastiComp’s most recent success has come in economy seating components. The company has had LCF 40 PA66 crossbow risers in the field for more than three years and has developed an integrated seat spreader and support component from its Complet LCF-PESU that has passed 16G kinetic testing and is Federal Aviation Register (FAR) 25-certified.
James Peters, associate director of science and technology, PPG Industries (Cheswick, Pa.), addressed the value of high-elongation glass fibers for aircraft interior applications that demand high impact resistance, such as overhead bins, galleys and low-demand flooring. Specifically discussed was PPG’s InnoFiber HP, a yarn for specialty fabrics that offers a 2.41g/cm3 fiber density, 2,910 MPa fiber strength and 74 GPa fiber modulus. According to Peters, the material offers approximately 25 percent greater strain-to-failure and approximately 20 percent greater strength than E-glass.
Peters showcased data collected by BGF Industries (Greensboro, N.C.) using a 7781-style (8-harness satin weave) fabric-based epoxy prepreg laminate with 43.8 percent InnoFiber HP glass fiber volume. Depending on the specific application, the impact resistance was improved 30 to 120 percent, but at lower density due to the fiber’s greater elongation.
Lightweight and fire safe
Always of critical interest to aircraft interiors manufacturers are new tools to help aerospace OEMs meet the industry’s stringent FST requirements.
Johnny Lincoln, president, Axiom Materials Inc. (Santa Ana, Calif.), discussed recent market-driven research and development work into low OSU/FST epoxy prepregs for aircraft interior components, including a resin system for Oxeon AB’s (Borås, Sweden) TeXtreme spread-tow fabrics. “There are a lot of benefits to using an epoxy system in lieu of a phenolic system,” said Lincoln. Even though fire-resistant (FR) epoxies typically cost more than modified phenolics (about $0.50/lb more), Lincoln proposed that quicker processing, low toxicity, zero volatile content and mechanical improvements support the introduction of these materials.
Axiom developed two custom solutions: AX-3180-7781, a woven E-glass/epoxy prepreg for sandwich panels and laminates; and AX-5180-TXT160, a carbon fiber/epoxy prepreg. The latter incorporates Oxeon’s trademarked TeXtreme spread-tow carbon fiber fabric. According to Lincoln, the AX-5180-TXT160 prepreg is less than half the weight of a 2-ply 3K plain-weave phenolic, yet it offers higher impact properties. When compared to a 0°/90° unidirectional carbon fiber/phenolic layup, the material is 10 percent lighter at the same strength.
Chris Kilbourn, global aerospace manager, DIAB Inc. (Laholm, Sweden) compared PES thermoplastic foam to traditional honeycomb for heat-resistant structures in aircraft interior applications. According to Kilbourn, PES foam offers a lighter weight (approximately 10 percent) and lower cost (from 10 to 50 percent) option to honeycomb core materials, while also offering greater flexibility during formation of free-form shapes. Specifically, DIAB offers Divinycell F PES foam for aircraft interior applications. The foam can be formed into complex shapes in hot or cold temperatures. Reportedly, the material’s microcellular structure does not require a film adhesive and bonds with most prepregs. Kilbourn showcased a free-form seat shell and IFE racks and monuments constructed of a sandwich structure that combines glass-reinforced phenolic and DIAB’s PES foam.
Zotek F foam was presented by Jim Baron, director of technical development at Technifab Inc. (Avon, Ohio). The self-extinguishing foam reportedly offers high tensile and mechanical strength and high rigidity at low temperatures. Unlike Teflon, which is composed exclusively of difluoromethylene units, the polyvinylidene fluoride (PVDF) foam is formed using a standard radical mechanism with an alternating methylene and difluoromethylene structure. “It has a burn resistance and activity resistance similar to Teflon, but is more easily molded,” said Baron. Void formation is achieved using high-temperature nitrogen gas infusion, which creates small voids (0.1 mm/0.004 inch to 0.4 mm/0.02 inch) that expand threefold after pressure and high temperature are applied again.
Zotek F38 HT, a typical end product, conforms to all FAR 25 standards. Its tensile strength is 780 kPa and its density is 38 kg/m3. In standard part production, a 1-inch/25.4-mm thick, 1m by 2m (3.3-ft by 6.6-ft) panel is skived to 7.2 mm/0.28 inch thick and cut via waterjet (or any standard blade) with a bevel and head-and-shoulder design. Insulation tubes were the first product developed for aircraft environmental cooling systems, according to Baron, who gave several examples of weight-saving opportunities using the foam. The replacement of silicon-foam dust seals could save 1.2 lb/0.5 kg per window, he reported. And the replacement of Kevlar ECS ducting could save more than 100 lb/45.4 kg per aircraft, he added.
Additive manufacturing with thermoplastics
Clint Newell, senior research manager, Direct Digital Manufacturing Group (DDM), Stratasys (Eden Prairie, Minn.), presented DDM’s fused deposition modeling (FDM) capabilities. FDM employs additive principles to fabricate 3-D parts directly from CAD files by depositing material layer by layer. The material — typically engineered thermoplastic — is filament-fed through a heated extrusion nozzle and deposited as a bead in a row, building the part layer by layer, explained Newell. “It’s possible to make fully dense parts or build in scaffolding to open up space and save material,” he explained.
For aircraft interior applications, Newell focused on FDM using select unfilled resins from SABIC (Pittsfield, Mass.). Ultem 9085 (PEI) reportedly offers a good balance of mechanical and thermal properties and is qualified for aerospace interior applications, said Newell. Stratasys manufactures smaller Dimension 3-D printers for models and prototypes and larger Fortus production systems for manufacturing tooling and parts.
Urethane ester hybrids for infusion
Closing out the conference was Rick Pauer, market manager, CCP Composites (N. Kansas City, Mo.), who presented research done in collaboration with Trevor Gundberg, director of composites engineering, Vectorply Corp. (Phenix City, Ala.), on infusion-grade thermosetting resins in high-performance fibers. “The belief that when you’re using carbon, you need to use epoxy is absolutely wrong,” said Pauer. “We should consider urethane ester hybrid resins for infusion.” Vinyl ester and urethane hybrids offer at least equivalent performance and process faster due to low viscosity, he added.