Truly a locus of aerospace composites activity, Wichita boasts both headquarters and manufacturing for Beechcraft, Cessna and Spirit AeroSystems, manufacturing for the Bombardier Learjet, and the National Institute of Aviation Research (NIAR) at Wichita State University. This 2013 location for SAMPE Tech provided the Wednesday keynote by Kansas Governor Sam Brownback, “The Importance of Advanced Materials to the Aviation Industry and the Rest of the World” as well as Thursday’s “Learjet 85 Product Development Highlights” by Pierre Harter, engineering director Learjet 85 structures.
Spirit AeroSystems also participated, with Trevor Angell’s review of a recent project with ElectroImpact (Multikeo, Wash.) to adapt current large automated fiber placement (AFP) machines to build smaller substructures vs. their current task of large fusleage panels and wing spars. The goal is to increase efficiency of existing machines in order to use composites in the smaller stiffeners and ribs that are currently titanium. Spirit also contributed via Mike Wadsworth’s presentation, “Novel Valve and Method for High Temperature Resin Infusion Control,” which described a patent-pending device that reportedly eliminates mechanical valves at injection and venting ports, reduces the number of bag penetrations and enables resin flow control to reduce “race tracking” and other flow-direction permeability variations, even beyond 425˚C/797˚F.
Out of autoclave (OOA) processing continued to be a theme, as did nanocomposites, toughening of epoxies, thermoplastic composites, automated manufacturing and damage modelling. The use of nondestructive testing (NDT) and structural health monitoring (SHM) dovetailed with presentations on adhesive bonding technology in a general quest for improved simulation — of both processing and damage/failure mechanisms — and validation of structural predictions. This was also mentioned in the panel discussion on “Qualification and Certification,” where the concern was voiced that today’s certification process — described as having evolved from a metallic aircraft background — restricts the uses and advantages of composites and inhibits development. Impact damage and how to certify composite structures for damage tolerance was cited as a key issue. For example, developing design allowables is expensive and time-consuming, but has been inherited from metal structure fail-safe and damage-growth guidelines; thus, composites are shoehorned into a certification process that does not accurately apply to how they are used and fail. The recent government push toward Integrated Computational Materials Engineering (ICME, and ICMSE if you add in “Science”) was mentioned, as was the Materials Genome Initiative, stating that currently it takes 20 years from test tube to insertion of a material into a manufacturing platform. Panelists asked, “How do we cut that signficantly? Can we indeed utilize CAD/CAM technology effectively within certification like the pharmaceutical industry does?” One responded that NASA, the Army, Navy and Air Force are all working together to start a national dialogue on composite structures certification.
Notable exhibitors among the 170 companies participating included Canadian firm BrookOne (Markham, Ontario), introducing its BrookOne Fire Barrier Film, which surpasses the four-minute heat flux test performance required by FAR 25.856(b), resisting flame penetration for more than 15 minutes. It also claims no delamination after scratch testing with weights from 100 to 500g, and ability to be rolled and folded without fire barrier degradation.
Virtek Vision International (Waterloo, Ontario, Canada) demonstrated its Iris SPS stereometric system. Sean Francoz, senior product manager at Gerber, noted that traditional projection systems rely on use of reference targets on the tool to determine part dimensions and accurately project ply placement locations. For large parts, however, traditional reference targets may be difficult to place near ply placement locations. Iris SPS is designed for such applications. First, the system locates the tool by searching for and identifying locator tabs on margins of the tool's surface. These allow the laser to reorient itself to the tool in case either the tool or the projector is moved. Then, Iris SPS uses line data from the part CAD drawing to project a series of reference lines on the tool where it "thinks" certain part features are located. Such features may include a straight line, an arc or a hole. The operator then uses a spotter to mark the actual points of the feature on the tool; Iris SPS uses these marked points to calibrate its exact location in preparation for projection and ply placement.
Electron Heat accelerated heating, drying and curing technology was released publicly for the first time by Riddle Technologies LLC. It combines a proprietary “sensitizer” additive of 1 to 2 percent (by weight) to a resin with radio frequency (RF) heating to reportedly reduce a traditional 24-hour room temperature cure of a 2-inch/51-mm thick section of polyester resin to less than two minutes. Inventor David Riddle claims to reduce cure time by tenfold for mid- to large-volume manufacturing, using one-tenth or less the energy of resistance-wired heated tools. The RF creates heat through electromagnetic radiation similar to but safer than a microwave due to longer wavelengths at 10 to 100 MHz, versus 2 GHz for a typical microwave. The sensitizer serves to focus this energy where crosslinking occurs. Thus, energy is directed to where it produces cure, resulKng in faster and more efficient processing. Other benefits cited include less thermal stress and microcracking (RF heating in general produces less heat), more even cure of thick and thin sections and capability for instant on/off or stop at a target temperature from 90°F to 500°F (32°C to 260°C) as well as specified dwells. The RF Power Converter is said to have a self-leveling feedback system that efficiently expends energy only as needed and can operate 24/7 with few parts subject to wear. Pulse or continuous heat is possible and the technology is touted as effective with polyesters, epoxies, BMI, polyimides, prepregs and adhesives.
North Thin Ply Technology (Penthalaz, Switzerland) introduced carbon fiber industry veteran, Mike Mettenet, as sales manager for North America. Thin Ply Technology (TPT) was invented in 2001 for sailmaking and used by Alinghi in the 2007 America’s Cup. North Technology Group (Milford, Conn.) created North TPT LLC in partnership with TPT’s Swiss inventors to develop and promote the technology for structural composites. North TPT has been used by Burton Snowboards (Burlington, Vt.), Movement Skis (Puidoux, Switzerland), BHR Aircraft Corp. (Anglet, France) and multiple teams in Formula 1 motorsports as well as several AC-72 sailboats raced in this year’s America’s Cup. With manufacturing facilities in Switzerland and Minden, Nev., NTPT offers dry and prepreg unidirectional spread tow tapes, as well as woven fabric prepregs that are a fraction of the areal weight of traditional materials. A paper presented at ICCM19 (July 28-Aug. 2, Montreal, Canada) compared quasi-isotropic laminates using 30 g/m2 (thin), 100 g/m2 (intermediate) and 300 g/m2 (thick) prepregs. Thin and intermediate materials required 10 and three times the plies, respectively vs. thick materials to build equivalent thickness laminates, but also showed much higher ultimate tensile strength (847 MPa and 832 MPa vs. 595 MPa) and onset of damage (822 MPa and 702 MPa vs. 248 MPa). Other improvements NTPT claims with its 30 g/m2 (gsm) materials: 25 percent higher compressive strength, 30 percent high tensile damage onset in notched laminates and 10x longer notched laminate life span.
Boyce Components (Phoenix, Ariz.) exhibited its Embedded Composite Heater (ECHOS) technologies, which include trowel-applied materials and a silkscreen-applied system using carbon nanotubes. Both create temperature-controlled thin laminates with tailorable watt densities for applications including radiant heating (a deicing system is in testing with an aircraft manufacturer) and temperature-controlled tooling.
Engineering Software Research and Development Inc. (ESRD, St. Louis, Mo., USA) has partnered with Advatech Pacific (San Bernadino, Calif., USA) to develop and supply 5th generation FEA software offering “certification by simulation” of composite structural designs. No longer requiring a separate test for each design change (e.g. 100 models-to-100 tests), this partnership instead offers a simplified approach that isolates the Uncertainty Quantification (UQ) step in the verification and validation process. The application of “certification by simulation” drastically reduces the need for physical experiments (e.g. 100 models-to-10 tests). ESRD’s StressCheck product is used to predict strength, durability and damage tolerance of metallic and composite airframe structures, and is endorsed by the U.S. Air Force/AFRL, NAVAIR, Northrop Grumman, Boeing, and Lockheed Martin, among others.