Charleston, S.C. was the setting for the latest CompositesWorld’s High Performance Fibers Conference, held Nov. 17-18, 2009 at the Doubletree Guest Suites Charleston-Historic District hotel. The event kicked off with a preconference seminar entitled “High Technology Fibers and Fabric Structures in Body Armor Applications,” presented by Dr. Bhuvenesh Goswami, the alumni distinguished professor emeritus in the School of Materials Science and Engineering at Clemson University (Clemson, S.C.). Dr. Goswami discussed the properties of fibers, yarns and woven and nonwoven fabrics and how fabric manufacturing and weave structure affects the mechanical and physical properties of fabrics. He emphasized that frictional energy dissipation is a key to ballistic protection, pointing out that the fabric needs to move in shear to absorb ballistic energy. Modeling of energy waves and fiber/fabric interaction is ongoing and is “a challenge,” according to Dr. Goswami. He also predicted that hybrid fabrics will grow in importance.
The conference began with introductions from cochairs Dana Granville and Scott Northrup. Granville, with the U.S. Army Research Laboratory at Aberdeen Proving Ground, Md., is senior materials engineer for the Materials Applications Branch of the Weapons and Materials Research Directorate. Northrup is the director of new business development at AGY (Aiken, S.C.), a manufacturer of high-strength S-2 Glass, and has an extensive background in glass fiber and advanced composites. Granville stood in for the absent Jean Herbert, chief of the fibers and material physics division at Natick Soldier RD&E Center (Natick, Mass.) and discussed recent composites and fiber research for the U.S. Army. Herbert’s group is involved in development of new, “smart” textiles for the war fighter and first responder (which have embedded sensors to detect explosives, for example) and fibers that can be configured for integral communication devices. Natick is involved with EY Technologies (Fall River, Mass.), a company that is currently producing a very fine wire fiber with a metallic center and polymer sheath. EY president Gerald Mauretti says the fiber can be woven as a smart textile and embedded in composite laminates for cure monitoring purposes and/or structural health monitoring. Other Natick research projects include piezoelectric fibers in clothing that could harvest motion energy from the wearer.
David Fecko, business development manager for defense at AGY, described his company’s new, trademarked Featherlight glass fiber, which delivers 5 to 10 percent greater strength than its S-2 Glass, due to its very small filament diameter, while reducing weight in ballistic applications. He reports that AGY is working with Natick researchers on sizing for ballistic applications that will be robust enough to provide structural strength yet capable of release in high-strain-rate scenarios to absorb impact energy.
Dr. Patrick Hook, managing director of Auxetix Ltd. (Tiverton, U.K.), introduced an intriguing new ballistic product. The company, a spinoff from the University of Exeter, licenses helical auxetic fibers — a reinforcement material with a negative Poisson’s ratio that causes an increase in diameter under tension. The product features a relatively elastic core fiber product overwrapped with a smaller-diameter, but relatively inextensible, fiber product. The analogy is to take a bungee cord, wrap it with a thin manila rope, then stretch it; because the rope can’t stretch like the bungee cord, it straightens, forcing the bungee to wrap around the rope, effectively creating a larger volume when in tension. Dr. Hook explained that Auxetix’s fabrics, trademarked Zetix, are extremely effective in blast mitigation situations because the fabric effectively vents the energy as it expands then returns to its original dimension. Zetix fabrics, therefore, are able to withstand multiple impact events. The company is targeting applications in cargo containers, body armor, military tents and aircraft armor, in which Zetix can be tailored with any elastic core fiber and any inextensible wrapping fiber.
During a presentation on lightweight composite integrated structural armor, Al Chan, program leader of Owens Corning’s (OC, Toledo, Ohio) North American Innovation Lab, said the company has begun production of S-glass for ballistic applications — an announcement that took many conference attendees by surprise because OC had previously spun off its S-2 Glass production in 1998 to an independent joint venture with Groupe Porcher Industries, initially known as Advanced Glassfiber Yarns, which emerged as AGY in 2004. OC, however, will not be producing trademarked S-2 Glass again, but instead, has developed a derivative S-glass based on the company’s Advantex technology and R-glass formulations. The new reinforcements, called ShieldStrand S (as well as XStrand S and FliteStrand S for different markets), can be made via a new direct-melt process that reportedly can produce glass fiber in volumes 50 times greater than that possible with traditional high-strength glass processing. Chan says the initial target end-market is large, complex structural armor that is integrated into a vehicle.
Tom Campbell, an engineer at Fiberforge (Glenwood Springs, Colo.), discussed the company’s activities related to thermoplastic hybrid composite helmet fabrication. The work was sponsored by the Army Research Laboratory, and results to date show that a structural shell with a ballistic overlay can be produced in less than an hour using Fiberforge’s automated tailored-blank fabrication methodology, but the company says that many opportunities exist for reducing cycle time.
Other presentations compared the relative merits of a variety of ballistic polyethylene and polypropylene fibers, including Honeywell Advanced Fibers and Composites’ (Colonial Heights, Va.) Spectra ultrahigh molecular weight polyethylene fiber and Spectra Shield and Gold Shield armor products; Milliken and Co.’s (Spartanburg, S.C.) Tegris polypropylene self-reinforced composite products and its recently introduced Tegris CTC, which combines carbon fiber with Tegris; and Innegrity LLC’s (Greer, S.C.) Innegra high-modulus polypropylene.
W.L. Gore & Assoc. Inc. (Elkton, Md.) presented its case for expanded polytetrafluoroethylene (ePTFE) fibers (DuPont’s Teflon is the well-known brand). Although PTFE fibers are chemical-resistant and temperature-stable, their low tensile strength, high density, large denier and slippery handling during the weaving process have limited their application. But, says Gore’s Norman Clough, the company’s stiffer ePTFE fiber forms have high tenacity and tensile modulus, smaller fiber diameters and customized fiber finishes that reportedly make them easier to weave and stabilize. Tom Foltz, director of business development at Specialty Materials Inc. (Lowell, Mass.), described his company’s SCS silicon carbide (SiC) fibers and boron fibers focusing particularly on the benefits of continuous fiber ceramic composites, which include a reduction in brittle fracture characteristics. He noted that potential SCS applications are growing, pointing out that they are already in use in Boeing 787 components and photovoltaic applications.
Exhibitor E.T. Horn Co. (La Mirada, Calif.), a specialty raw material distributor, was on hand to showcase Kamenny Vek (Dubna, Russia) Basfiber basalt fiber in direct roving, assembled roving, chopped strand and twisted yarn forms. Kamenny Vek claims its basalt fibers exhibit 15 to 20 percent higher tensile strength and modulus, better chemical resistance and less water absorption than standard E-glass, with properties that approach those of high-performance glass but at a lower cost.