CompositesWorld

MAR 2017

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MARCH 2017 52 CompositesWorld FOCUS ON DESIGN Carbon composite driveshaft: Tailorable performance This racing and aftermarket specialist designs and produces custom driveshafts for multiple markets. » Every gearhead knows that the transfer of power from an engine to the axle and drive wheel in a rear-wheel drive vehicle requires a driveshaft, and that this highly loaded part is typically made of steel or aluminum. When composites became more widely available in the early 1980s, carmakers recognized that a carbon fiber composite driveshaft could bring significant benefits unavailable with metal designs, and several production vehicles were so equipped through the early 2000s (see Learn More, p. 55). Nevertheless, OEMs never fully embraced composite driveshafts, due to shifts to front-wheel-drive cars (which don't need drive- shafts), four-wheel drive vehicles (which use shorter shafts, for which metals suffice) and the always-present composite/metal cost differential. Yet, in some corners, composite driveshafts never went away, and there are numerous manufacturers who have prospered making shafts for race cars, hot rods and specialty applications. One of these is QA1 Precision Products Inc. (Lakeville, MN, US), founded in 1993. A specialist in driveshafts, QA1 also turns out bearings, suspension elements and shock absorbers for the full gamut of racing disci- plines. "e technology governing composite driveshafts is better today, not just in materials but also in faster manufacturing and assembly," asserts Travis Gorsuch, QA1's director of advanced mate- rials. "Composite shafts offer many benefits." Custom designs for customer applications In a nutshell, several performance factors interact in drive- shaft design. Basically a thin-walled hollow tube, a driveshaft must have adequate stiffness to resist buckling under a speci- fied engine torque output, which might be, for example, 2,500 lb-ft in a high-end, 500-cubic-inch race engine turning at 8,000 rpm. Although the universal joint connections at each end of the driveshaft relieve much of the stress in the drivetrain due to the changing angles, the shaft must perform well because the rear axle constantly moves in relation to the engine. And perhaps most important to the design, the driveshaft must be stiff enough that its natural resonant frequency is higher than that of the engine and the rear axle, so that it does not create destructive resonant vibration. at is, critical speed — the point at which the driveshaft's rotational speed and its natural frequency coincide, augmenting vibration to the point of instability — defines the frequency of the first order bending mode. At this point, the driveshaft will undergo ampli- fied displacements, which can cause the shaft to bend or even whip, and ultimately destroy itself. Damping strategies to control first- order vibrations can be employed, By Sara Black / Senior Editor Lighter and stronger than metals An all-composite, filament-wound driveshaft fabricated by QA1 (Lakeville, MN, US) is commonly three times stronger at half the weight than a metallic version. Custom metallic end-fittings, appropriate to a specific vehicle type, are attached to the ends of the composite shafts in a proprietary 11-step bonding process. Source (all photos) QA1 Precision Products

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