CompositesWorld
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85 CompositesWorld.com NEWS N E W S N S N E W S E N W S W Composites Tackle Concussions "When we saw the Clemson exhibit demonstrating the forces associated with head injuries," says Cates, "we naturally thought of the hot-button issue related to football and concussions." Innegra already supplies its Innegra S and H fbers to customers who manufacture helmets for whitewater kayaking and other extreme sports that present the potential for impacts equal to or greater than those in football, so it seemed plausible to Cates and her team that these same materials could provide benefts in the design of a football helmet. Soon thereafter, Innegra and Shelby, NC, US-based fberglass supplier B & W Fiberglass (already a partner/supplier in the production of the Innegra H fber), approached Clemson's bio-engineering department about the possibility of a partnership in a study to evaluate the properties and performance of composite materials and their suitability for a potential application in the outer shell of a football helmet. Te frst phase of the project, a materials characterization study, was completed in 2014. About 25 materials were tested to ASTM D7136-12 "Standard Test Method for Measuring the Damage Resistance of a Fiber-Reinforced Polymer Matrix Composite to a Drop-Weight Impact Event." Te basic test setup comprised a drop sled system called a "cushion tester," a high-speed camera and an analysis computer. A fat panel sample coupon of each material of interest is placed into a fxture at the base of the drop sled where it is subjected to impact by an object of a specifed weight and shape. Sensors measure velocity of impact and sample displacement, while a high-speed camera records rebound velocity and contact time. Tese values, in turn, are used to calculate the impact coef- fcient of restitution and energy absorption. Tese are the key parameters for materials intended for use in applications subject to multiple and continual impacts. Tey provided the study with a baseline distinction between the various samples. Te initial materials tested were, by design, simple, consisting of a single reinforcement material and an of-the-shelf epoxy. Fibers tested included various types of glass and carbon as well as Innegra's olefn-based S-fber, and also the company's H-fber, a hybrid yarn, consisting of its S fber combined with another high-modulus fber, such as carbon, S-glass or basalt. "We delib- erately tested simple systems because we wanted to specifcally focus on fber behavior in this phase," says Cates. Included in the initial round of testing were control fat-panel samples of neat PC and ABS. Although the project entailed evaluating elementary composite structures, the early fndings are reportedly promising, pointing to signifcant diferences in the performance of compos- ites with respect to both controls. "We've seen some remarkable results thus far with the various fbers we've tested, indicating composites could provide superior protection against the types of impacts and forces generated in football," says John DesJardins, who is the Hambright Leadership associate professor of bio-engineering at Clemson. DesJardins, who is collaborating closely on this project with Dr. Greg Batt, Clemson's assistant professor of Food and Packaging Science, notes that poly- carbonate has high impact resistance but is not very good in terms of energy dissipation. Tis property makes both PC and ABS good at withstanding repeated impacts without breaking, but not so good at mitigating concussion-causing forces. SIDE STORY Head safety initiative to fund research Sponsored by the National Football League, GE (Fairfeld, CT, US), the National Institute of Standards and Technology (Gaithersburg, MD, US) and sports apparel maker Under Armour (Baltimore, MD, US), the 2015 Head Health Challenge III will reward up to US$3 million to companies and organizations that deliver novel materials to address and mitigate concussion risks in football and other sports. Clemson University (Clemson, SC, US) associate professor of bioengineering John DesJardins says his team is currently conducting research on potential composite materials for football helmets (see main story) and will participate in the Challenge. Quantifying a range and threshold for concussions Researchers who studied flm of concussion- causing collisions in the NFL identifed a range in which concussions occur, between 72G and 125G with a duration of 14-16 milliseconds. The bioengineering objective of a composite helmet is to increase the impact duration, thus reducing the acceleration of the head well below the threshold G-force value of 72G. Source | Clemson Bioengineering 400 350 300 250 200 150 100 50 Head Drops Skull Fracture Pressure Loading on Brain Estimates from Volunteers Source of Historic Human Tolerance Data SI = Severity Index Majority of Biomechanical Data Peak Acceleration (G) 2 4 6 8 10 12 14 16 18 20 NFL Data Time (ms) SI=1200 SI=300 a=125G a=72G NFL Concussions H e S k u l M a j o r i t y o f B i o m e c h a n i c a N F L C o n c u s s i o n