CompositesWorld
Issue link: https://cw.epubxp.com/i/546021
AUGUST 2015 CompositesWorld 64 FOCUS ON DESIGN High-tech + trial & error Hyperco had the advantage of proprietary and established in-house spring development programs and testing equipment. Says Hazard, "We knew the characteristics we wanted to achieve, so we built and tested our designs in a trial-and-error process, and used that data to adjust the mathematical formulas, then went back to producing more prototypes, in an iterative fashion." Disc iterations were compression molded from woven carbon/ epoxy prepreg supplied by TCR Composites Inc. (Ogden, UT, US), prepregged Qiso slit braid from A&P; Technology Inc. (Cincin- nati, OH, US) and materials from other suppliers. Tree basic disc designs were molded: F-type discs have a small outer fange; L-types have a lip that centers the mating F-type fange (see drawing, p. 63); and N-types have no fange or lip, and are used as the last disc in a stack, to provide a solid carbon surface on the spring perch. "Te layup varies," Campbell says, explaining, "We've created 'families' of disc sizes, and can create diferent spring rates by varying disc thickness and fber orientations." Hyperco is working on establishing design standards for the discs, to make information available for CAD software programs and to raise awareness of the technology for engineers. Prototype discs underwent C-scan nondestructive inspec- tion followed by spring rate testing on Hyperco's high-accuracy machine from Larson Systems Inc. (Minneapolis, MN, US), equipped with sensors and special software that provided data on spring rate and hysteresis based on defection measurements. Special fxtures were required to test individual discs and disc stacks, says Hazard. Testing included long-term cyclic fatigue, with load cell setups at high frequency to detect creep or fatigue failure. Te data show that pitch angles between 7° and 10° are possible, depending on the application, and allow an appropriate degree of defection and spring rate at desired loads. Further, the optimum window for OD/ID ratio ranges from 1.7 to 2.2, "to optimize the amount of storable energy vs. the design envelope," that is, the chassis space available for spring installation, says Hazard. Hyperco's refned in-house molding processes now yield discs consistently within ±2% of the designated disc spring's spring rate, and Campbell points out that the carbon composite ofers better repeatable rate change during spring compression than steel. Hazard adds that it is possible to design in some friction between discs to achieve damping for energy control, perhaps not for motorsports, but for other industry applications for which the company has begun testing. Track-proven Te beauty of the CCBS for motorsports, explains Campbell, is that racers can "tune" disc stacks, with higher or lower spring rates, to match track conditions. "Although our standard size range is optimum, we can also produce custom sizes for specifc needs," adds Hazard. A number of amateur racers, among them Sports Car Club of America (SCCA) national champion Chris Farrell (see photos, p. 62) have adopted the CCBS, with great success. Although it costs more than a metal coil spring, its "tunability" is appealing. When racers factor in several diferent sets of steel springs for diferent tracks/conditions, the price-per-rate cost is competitive. Unfortunately, US pro racing organizations, including NASCAR, IndyCar, IMSA and NHRA, have ruled out carbon disc springs, for now. But Campbell contends, "As with any new technology, accep- tance takes time and we believe … they will allow it in the future." "Lightweighting in automotive is a huge issue now," concludes Hazard, "and no one else is approaching the issue of lighter springs like we are." Read this article online | short. compositesworld.com/DiscSpring Hyperco's Mark Campbell unveiled the CCBS "Bellows Spring" at CW's Carbon Fiber 2013. Read about it online | short.compositesworld.com/ALTDgT6F Greater control of a key spring variable Hyperco's CCBS discs are molded in the style of Belleville washers, and are avail- able in a variety of sizes capable of producing a variety of spring rates. Greater design freedom and market potential The CCBS disc springs are adaptable to, and "tunable" for desired performance in, a variety of aerospace, industrial and recreational applications, including motorcycles. Sara Black is CW's technical editor and has served on the CW staf for 17 years. sara@compositesworld.com