CompositesWorld
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55 CompositesWorld.com Gorsuch adds that the company has researched the use of high- stiffness, pitch-based carbon fiber, as well as combining fibers of different moduli in a single part, but, he adds, "while it helps to increase performance, it becomes difficult since it adds manufac- turing cost." After a filament-wound shaft is completed on the company's McClean Anderson (Schofield, WI, US)-supplied filament winding machine, it is wrapped with compaction tape and oven-cured in QA1's custom oven, built in-house for tailorable ramp and dwell cycles. After cure, a shaft is cut to length and a small piece is cut from one end, which undergoes microscopic inspection, using Olympus Stream image analysis software, from Olympus Corp. (Waltham, MA, US), to validate fiber volume, fiber angle and void content. "With this image analysis software, we can verify that the void and fiber volume meet our specifications. In addition, we verify layer thickness and fiber angle," says Gorsuch. e image analysis inspection is followed by mechanical testing, then metallic end fittings are attached, via QA1's propri- etary 11-step bonding process. Next, shafts are torsion tested in house, says Gorsuch: "is is a very vital part of our process, and allows us not only to validate our FEA modeling by showing that a shaft performs as modeled and that simulations are appropriate, but also to ensure the quality of every driveshaft we produce." For specific markets, the testing certifies that driveshafts meet racing quality assurance overseer SFI Foundation Inc.'s (Poway, CA, US) driveshaft specification 43.1. is is followed by a balancing test, to ensure no vibration at operational speeds. "Our designs are commonly three times stronger than a metallic shaft, and come in at about half the weight," asserts Gorsuch. at alone is a huge benefit: Overall vehicle weight and engine power loss from rotating a heavier metallic shaft are significantly reduced, with no impact on performance. But there's more. From a safety standpoint, the composite will splinter upon impact in the event of a crash, preventing additional damage to the vehicle and its occupants. at's not the case with a metallic shaft, Gorsuch adds, which can fail catastrophically. Last, but not least, compos- ites offer better corrosion resistance. Concludes Gorsuch, "Drivers want more in their cars today, and a lighter driveshaft reduces rotating weight and overall vehicle weight. I believe there's a trend toward greater adoption of composite driveshafts." Carbon Composite Driveshaft Sara Black is CW's technical editor and has served on the CW staff for 19 years. sara@compositesworld.com Read this article online | short. compositesworld.com/CompDSCF Read about a filament wound driveshaft the developers of which hope will qualify for a helicopter application in "OOA: Thermoplastic alternative targets performance spec" | short.compositesworld.com/OOA-TPC The composite driveshaft appealed first to racing and supercar enthusiasts, to whom performance was paramount and cost was secondary. But the advan- tages of composites — reduced vehicle weight, greater corrosion resistance and others — overcame the disadvantage of higher upfront cost for a time, among some mainstream automakers as well. A few high-production vehicles well outside the supercar category were equipped by OEMs with composite driveshafts from the 1980s through the early 2000s, including the Nissan 350, Mazda RX8, Mitsubishi Montero, and Ford E100 Econoline vans. During this period, there also was a notable hybrid driveshaft design success. From 1986 to 1996, Strongwell (Bristol, VA, US) manufactured the trademarked Spicer Graph Lite driveshaft for customer Dana Inc.'s (Maumee, OH, US) Spicer driveshaft division, starting with General Motors' model year 1988 GMT-400 pickup trucks. The opportunity arose, says Strongwell R&D; manager Joe Spanovich, because the truck's design allowed a maximum of 100 mm within the chassis for the driveshaft. A full-length, one-piece aluminum shaft had insufficient stiffness, and Dana engineers did not want to install a two-piece steel shaft with a bearing, which would add assembly time, cost and complexity. Strongwell devised a method to pultrude axial carbon fiber tows over an aluminum tube to create a hybrid metal/composite shaft. "Many, many tests were done, severe tests, that took months to complete," says Spanovich. "But it was a lower-risk solution than an all-composite part." The aluminum shaft, which acted as a traveling mandrel, was first covered with a polyester surface veil/isolation barrier, to prevent galvanic corrosion. Unidirectional carbon fiber tows from Hercules, later part of Hexcel (Stamford, CT, US), were pulled through a resin bath of DERAKANE epoxy vinyl ester (supplied by Dow Chemical Co., Midland, MI, US, a resin later acquired by Ashland Performance Materials, Columbus, OH, US), and laid lengthwise against the veil. The carbon-covered tube then exited through a precision bushing and a winder that wrapped the carbon tows with glass roving. Finally, another polyester veil was placed over the entire shaft, for added corrosion resistance. The hybrid driveshaft was 60% lighter than the two-piece steel alternative, and saved 9.1 kg per vehicle. The longitudinal carbon fiber tows stiffened the aluminum shaft sufficiently that it could handle vehicle torque without resonant vibrations, says Spanovich. At peak production, the company made 50,000 parts per month. "At that time, we were the largest consumer of carbon fiber in the world," he recalls. Although early mass-production efforts were largely abandoned and OEMs did not fully embrace them, composite driveshafts are still produced by special- ists for race cars, hot rods and other specialty applications. Composite driveshafts in production vehicles SIDE STORY