CompositesWorld
Issue link: https://cw.epubxp.com/i/576646
OCTOBER 2015 84 CompositesWorld FEATURE / COMPOSITES IN HEADGEAR time we have continually been tinkering with the formula and the manufacturing process," he says, reporting the helmets are hand- layed, bagged and oven-cured at 140°C. "Cracking is not an issue for the current model." As for the two-year stated lifetime, Simpson says when SG Helmets started the helmet certifcation process with the National Operating Committee on Standards for Athletic Equipment (NOCSAE), he was required to give an expected lifespan and simply stated "two" without a clear understanding of the football helmet market or certifcation process. "Our helmet's expected lifespan," he says," is 10 years like every other helmet on the market." The physics of concussions: The brain/shell interface It's important to note that helmet design, here, is complicated by the fact that American football is, above all, a contact sport. Stefan Duma, the director of Virginia Tech's School of Biomedical Engi- neering and Sciences, says two major factors determine a helmet's performance and rating. "Te highest-rated helmets," Duma says, "protect against high-impact hits, but they also protect against medium- to low-impact collisions, which players experience much more often." It's not just about the Big Hit. Tis "duality" related to the helmet shell's protective capabili- ties, the material impact resistance and toughness necessary to provide 10-year durability, and the need to compete on price point (the SG is about 20% more expensive than other top-rated brands), make designing and manufacturing a composite football helmet for mass-market use a challenging undertaking. Innegra's Cates says her company was inspired recently to take a fresh, blank-slate approach to the challenge after seeing a "concussion simulator" developed by bio-engineering researchers at Clemson University (Clemson, SC, US) for the Roper Mountain Science Center in Greenville, SC. It consisted of a test dummy's head and upper torso, similar to the type used in Karate training. An accelerometer mounted in the head monitored the G-forces upon receiving a blow from a member of the audience, with a display screen indicating if a concussion threshold was reached. SIDE STORY Football participation tops in high school Professional American football garners much of the media limelight, but thumbnail statistics published by USA Football illustrate the potential magnitude of the football helmet market outside the pro ranks. In 2010-2011, football led the way in terms of total number of participants among all high school sports, with 1,134,000 athletes playing the sport at freshman, junior varsity and varsity levels. College, of course, represents another tier of football participation. According to NCAA statistics, colleges with active football programs at the Division 1, 2 and 3 levels currently number 120, 149 and 236, respectively. Further, at most universities football is the major revenue source for funding of all other sports programs. In the 2012-2013 school term, average revenue among Division 1 schools was US$15.1 million per school. University (Virginia Tech, Blacksburg, VA, US). Researchers at the school took more than a decade's worth of head/helmet accelera- tion data collected on Virginia Tech football players and mapped it to a laboratory test system that collects more than 120 points of impact test data on each helmet, measuring its ability to absorb energy and reduce head acceleration. Results of the rating system, called the Virginia Tech Helmet Ratings, are posted at www.sbes. vt.edu/helmet.php. Tus far, the program has tested 26 commer- cial football helmets, 25 made with polycarbonate or ABS shells, and the composite-shelled SG Simpson. Along with its fve-star rating, however, the SG's posted result was accompanied by several warnings, including one about cracking in the internal padding — not the composite — and a caution to consumers about a stated lifetime for the SG of two years, when the expected lifetime of a PC helmet is typically 10 years. SG Helmets president Bill Simpson takes issue with both. "We built the frst prototype of the helmet in 2010, and since that Helmet R&D;: Materials characterization The frst phase of testing, designed to characterize a selection of basic fber-reinforced materials as poten- tially suitable for use in the shell of a football helmet, was conducted at Clemson's bioengineering lab. The test set up, conducted to the ASTM D 7136-12 standard, comprises a drop sled or "cushion tester," a high-speed camera and an analysis computer. Sensors measure velocity impact and sample displacement, while the camera records rebound velocity and contact time. Source | Clemson Bioengineering