CompositesWorld
Issue link: https://cw.epubxp.com/i/681810
47 CompositesWorld.com Superlight Road Bike Frame Wais says conventional bicycle develop- ment involves making several prototypes and then testing each to determine which design performs best. Most critical in this process is that the frame meet certain strength and stifness requirements established by the Zedler Institute (Ludwigsburg, Germany). Designing a frame at a competitive weight that also could pass the Zedler tests would be a real challenge. Wais wanted to limit as much as possible, if not eliminate, this expensive trial-and-error development process: "I refused to believe that there weren't tools out there that allowed us to do all of the design work virtually." With that in mind, he started asking around the composites industry and, eventually, settled on Altair Engineering (Troy, MI, US). "We went to Altair and said, 'We really need your help and we want to be smart about this,'" Wais recalls. Rolo also did not want to invest the money, time and intellectual capital required to acquire and learn to use design simulation software. So, it opted to use Altair's design services. Tat's when Altair's team manager, Kate Fisher, entered the picture. Working remotely and in person with Rolo engineers, Fisher says she frst created a virtual test structure that emulates the type used in Zedler tests. Into it, she placed a fnite element model of the Rolo frame. Next, she looked at strength and stifness targets set by Wais: • Bottom bracket stifness: >65 N/mm • Head tube stifness: >96 Nm/deg Te design optimization process, performed using Altair's OptiStruct product, followed three steps. First, starting with a 0°/±45°/90° ply schedule, Fisher conducted what's called free element sizing, which basically determines where on the frame plies should be placed to meet stifness targets. Te result, she says, is an "organic-looking patchy structure" that highlights the frame's fundamental design elements. Second, Fisher conducted sizing, which is an assessment of how much material to put where to create the thicknesses required. Tis step, she says, depends on the type of prepreg used. "Te frst two stages are the most crucial: Where to put each material — and how much," she says. Te third and fnal step is sequencing — a shufing of the ply order to fne-tune stifness and to avoid consecutive plies oriented in the same direction. Most of the optimization, say Fisher and Wais, was in the head tube and bottom bracket, which sufered in the original design from less-than-adequate reinforcement application. Says Fisher: "Te additional [optimized] mass that was added in the thickest areas was compensated for by taking out material in other, less-critical areas." "Once these steps were done, we went back to our virtual test rig to see how the design performed," Fisher says. In short, it passed. Not only that, but the new frame checked in at <700g, 14% lighter than its baseline predecessor. "More importantly," reports Fisher, "we now have a design that is much easier to manufacture. Plies are relatively large and edges are very clear and easy to see and place." Proof in the prototypes With a new, optimized design and new plybook in hand, Rolo then went to work proving that the virtual results could be replicated in the real world. "We had a reasonable idea from the simulation that the prototypes would be pretty close," says Wais. Indeed, although the new design required a few "tweaks," on the whole, they matched up well. "Te target we set for the head tube stifness was over 96 Nm/deg, and the bottom bracket stifness target was over 65 N/mm," says Wais. "We are on target for the head tube and way over on the bottom bracket." Further, with the design simulation process proven, Rolo has simplifed its manufacturing path for future bikes. Te entire process, frst time around, says Fisher, took about fve weeks. "Te most difcult part is building your virtual test rig and making sure that the baseline design is robust," Fisher says. "Once these things are in place, it becomes a much easier process." "Now, based on what we know," says Wais. "I think we would be pretty confdent going straight from simulation right to production tooling with only minor modifcations." With the optimized design and more efcient manufacturing process that results, Wais hopes to drive down overall cost. As a result, a fully assembled Rolo bike today runs €14,000-€15,000 (US$15,900-US$17,000), but Wais thinks he can bring the bike's price point down to €11,000 (US$12,500). "Tere is so much we can simulate," Wais says, thinking about the future. "We are only at the very beginning." Jef Sloan is editor-in-chief of CompositesWorld and has been engaged in plastics- and composites-industry journalism for 22 years. jef@compositesworld.com Altair's design optimization work not only hit the <700g weight target, but in the process, helped streamline manufacturing because the resulting plybook calls for fewer, larger plies, with cleaner, clearer edges that make layup simpler and faster. This is evident in the frame's transition points, which belie the structure's single-piece design. Source | Rolo Bikes