CompositesWorld
Issue link: https://cw.epubxp.com/i/532917
JULY 2015 CompositesWorld 48 FOCUS ON DESIGN sofware package. Te frst vibrational mode was torsional, meaning that the door's trailing edge would have a tendency to twist relative to the hinge line. Tis reinforced Edward's conclusion that more bias plies were a must. Te Atkins team ultimately developed four door designs: 1) a sin- gle aluminum piece, 40 mm thick; 2) a composite sandwich panel with 6-mm UD facesheets and 38-mm-thick core; 3) a composite sand- wich with 7-mm woven prepreg facesheets with 36-mm-thick core; and 4) a composite sandwich with 7-mm- thick facesheets made up of a combination of UD tapes and woven fabric prepreg, with a 38-mm-thick core. Te 7-mm facesheet requires an approxi- mate 28-ply layup. Edwards makes clear that the alumi- num design exhibited the smallest maxi- mum defection. But, in addition to weigh- ing almost four times more than the composite solution (70 kg vs. 19 kg), it exhibited a much lower frst natural frequency (61 Hz), indicating a propen- sity for undesirable vibration when deployed. Fig. 2 shows the four designs in terms of maximum strain results; Edwards points out that while stress concentrations occur at hole edges closest to the actuator arm, the use of ±45° plies increased the frst natural fre- quency and reduced overall strain values. "We conducted Tsai-Hill ply failure analysis in the FEA solver to ensure that there were no predicted failures in the higher strain regions," he says, conclud- ing, "Te cored composite is the most structurally efcient design." Edwards notes that Bloodhound engineers will make the fnal selec- tion from among the three cored designs. AN OPPORTUNITY FOR STEM STUDENTS Te impending run at the 1,000-mph threshold has captured the imagination of thousands of followers. Noble is keen to lif aware- ness in UK schools and stimulate student interest, using a wide range of math and engineering problems related to the car's design. In fact, Bloodhound team members regularly lecture in schools, and post math questions online about vehicle systems. When Edwards visited Seattle to deliver a presentation at the SAMPE conference in May 2014, he also gave a talk on propulsion to students at nearby Raisbeck Aviation High School. And student teams in the UK are even building rocket-powered scale models of the Bloodhound. Provided that Hakskeen Pan is dry and ready, the Bloodhound's frst high-speed runs could commence late this year. Edwards says these will take the car up to around 800 mph, which in itself would be a world record. Low-speed UK runway tests are scheduled for earlier in 2015. Te full-on "1,000" run likely will occur sometime in 2016. Bloodhound's driver, Andy Green, has said in his monthly diary, "It's easy to forget the most important part of building the world's frst 1,000-mph car: Getting to 1,000 mph safely is not just about technology, it's about engineering expertise…." Te world will be watching this engineering marvel in its record quest. Read this article online | short.compositesworld.com/Bloodhound See an animation of the Bloodhound SSC air brakes in action on the Bloodhound Web site | short.compositesworld.com/BSSC-AM See a recent math exercise about the Bloodhound SSC air brake system posed for students — and the answer — on the team's Web site | short.compositesworld.com/BSSC-mathx The Bloodhound SSC Web site has an extraordinary amount of information, including all CAD drawings, for the vehicle and its systems | short.compositesworld.com/BSSC-CAD Sara Black is CW's technical editor and has served on the CW staf for 17 years. sara@compositesworld.com FIG. 1: Deployed air brakes This CAD drawing of the Bloodhound's ram-actuated air brakes shows the brake panels in the deployed position. After air drag brings the vehicle's speed down from (it is hoped) record-setting levels, the brakes are designed to deploy and slow the car in the range from 1,300 to 300 kmh, at which point the car's wheel brakes will be engaged. FIG. 2: Sandwich construction options Von-Mises stresses are shown for the four airbrake designs, clockwise from top left, 40-mm-thick aluminum, sandwich panel with uni carbon tape face sheets and 38-mm core, sandwich panel with 7-mm-thick facesheets of woven carbon prepreg and 36-mm-thick core, and (lower left) sandwich panel with 7-mm-thick facesheets that combine uni and woven material with a 38-mm-thick core.