High-Performance Composites is read by qualified composites industry professionals in the fields of continuous carbon fiber and other high-performance composites as well as the associated end-markets of aerospace, military, and automotive.
Issue link: https://hpc.epubxp.com/i/302679
M A Y 2 0 1 4 | 5 7 duty Navy aircraft, the CH-46E SeaKnight helicopter. VX Aero has designed, proto- typed and produced more than six-dozen unique composite components for that craft, many replacing aluminum parts. A comparatively small frm, VX Aero - space thrives on its ability to innovate quickly and cost-effectively. Skillen cred- its that, in large part, to today's comput- er-aided modeling (CAM) and computer numerical control (CNC) machining technologies, which speed product de- velopment, and the advent of high-qual- ity OOA processing: Parts are layed up in the company's 4,000-ft 2 (372m 2 ) clean- room and then cured in its 40-ft by 12-ft by 10-ft high (12m by 4m by 3m) propane- fred oven. Complete cure cycle logs are printed and saved for traceability, thanks to a Yokogawa (Tokyo, Japan) digital temperature controller and DASYLab data recording software from Measure- ment Computing Corp. (Norton, Mass.). Together, these tools have helped level the playing feld in his case, says Skillen, between big and small manufacturers in terms of capability. But he also places special emphasis on his company's will- ingness to adopt new composite mate- rials — most recently, thin, biaxial rein- forcements called C-PLY. Why C-PLY? "My frst exposure to the concept which later became C-PLY was as a student in Dr. Stephen Tsai's 'Composite Design Workshop' offered by Stanford [Univer- sity]," says Skillen. "The approach made a lot of sense," he recalls. "Rather than try to make laminates that approximate isotropic materials, C-PLY is designed around the fber properties and ply ori- entations (angles) that enhance laminate performance." (See "Learn More," p. 64.) C-PLY combines several positive traits: It is a noncrimp fabric (NCF), it features anisotropic biaxial construc- tion, and its fbers are oriented at a low angle — it is sometimes described as "bi-angle" due to its 0°/θ° construction, where a low value of θ, e.g., 20° to 30°, reduces interlaminar stress, enhancing load transfer between plies without ma- trix cracking. Further, its spread-tow con- struction makes it remarkably thin. Although quasi-isotropic symmetric lay-ups (traditional "black aluminum") are commonly used in composites be - cause they mimic the properties of the metals they replace, computer-based an- alytical tools enable detailed ply-by-ply analysis, allowing designers to exploit the benefts of low-angle anisotropic design. The end result is better proper- ties for the same weight or as much as 40 percent less weight than an aluminum structure for similar performance. The use of a larger number of very thin plies reduces interlaminar stress and en - hances toughness. "Like in a beetle shell, an optimized composite theoretically would have layers just a few fbers thick," explains Skillen. C-PLY uses 12K, 24K, 48K or 50K tow, spread very thin but with- out gaps. The 12K spread tows VX Aero- space has used so far (0.003-inch/0.076- mm ply thickness) are much thinner than most unidirectional (UD) prepregs and weigh in at only 75 g/m 2 (2.2 oz/yd 2 ). VX Aero expects to have a steady source for the new material. Chomarat is installing a production line (sched- uled to be operational by mid-year 2014) capable of producing any stitched mul- tiaxial confguration, but optimized to produce 100-inch/2.5m wide NCF with angles from 30° to 90°. Multiaxials with angles of less than 30° are available in a reduced width. Skillen emphasizes that the stitched two-ply fabric VX Aerospace has been using — totaling 0.006-inch (0.152-mm) thickness and 150-g/m 2 (4.4- oz/yd 2 ) weight per layer — is tailored for structural loads but is far easier to Redesigned for productivity The heart of the VX Aerospace design for the U.S. version of the Falcon airframe is its wingbox assembly, anchored by a 3-D woven carbon fiber composite spar box. Self-rigging assemblies are used to cut production cost and time by using dimensionally accurate structures — in this case the spar box — to locate and align the next higher assembly — for the Falcon, that includes seat beams, wing roots and wing spars. Canopy Glare Shield/Rail Firewall FALCON AIRFRAME Center Spar Box Gussets Wing Spar Connect Wing Root WING BOX ASSEMBLY Aft Seat Beam Forward Seat Beam Source: VX Aerospace 0514HPC IM PlantTour-OK.indd 57 4/22/2014 3:57:36 PM