Composites professionals from around the world took home technical insights, and innovative design ideas from the High-Performance Fibers 2008 Conference, held Oct. 28-29, 2008, in Charleston, S.C. Organized by CompositesWorld Conferences, HPF 2008 was cochaired by Dana Granville, senior materials engineer for the Weapons and Materials Research Directorate of the U.S. Army Research Laboratory (Adelphi, Md.), and David Carlson, sales manager, ballistics for Teijin Aramid USA (Conyers, Ga.).
Scott Beckwith, president of BTG Composites Inc. (Taylorsville, Utah) kicked off the proceedings with a preconference seminar entitled, “Fiber Reinforced Composites for High Temperature Applications.” The presentation included a comparative overview of the mechanical properties of various types of glass, carbon, graphite, aramid, boron and organic fibers. Boron fiber offers a tensile strength and tensile modulus comparable to or better than PAN-based carbon fiber at about half the density. Its high cost, however — $700/lb — usually limits boron fiber to high-end aerospace applications that require improvements in compression load beyond what can be achieved with carbon fiber. Beckwith cautioned the audience to take care when sourcing E-glass in developing countries, con-tending that lack of proper quality control in these locations often can produce E-glass with sufficient stiffness but highly variable strength.
At the formal conference opening, Granville commented that composites in military applications continue to see robust growth, primarily as a result of increasing knowledge of the materials and, secondarily, on the strength of new design capabilities. He noted, by way of example, that the F-35 Lightning II Joint Strike Fighter will be 40 percent composites and that the U.S. Navy is planning to significantly increase the amount of composites, primarily glass-reinforced, used in the manufacture of ships, such as the DDG-1000 Zumwalt destroyer. He also reported that the U.S. Army is on a mission to lightweight its heavily armored combat vehicles through expanded use of fiber-reinforced materials. The goal is to build combat vehicles that use less fuel and can be more easily transported aboard C-130 military aircraft.
In his keynote speech, Tucker Norton, global technology manager, ballistic threat protection at DuPont Advanced Fiber Systems (Richmond, Va.), said that design, wearability and comfort are now on equal footing with performance in the manufacture of ballistic protection wear. He claimed that DuPont’s new Kevlar XP enables at least 10 percent lighter vest design yet meets stringent NIJ Level IIIA ballistic protection test requirements. He reported that vests made from Kevlar XP typically stop .44 magnum bullets within the first three layers of an 11-layer vest.
High-modulus polypropylene (HMPP) was the topic of a presentation made by Innegrity LLC (Greer, S.C.). The company’s Innegra HMPP reportedly can replace about half the total amount of aramid fiber in body armor with no drop-off in ballistic performance, per V50 (9 mm) test requirements. The V50 is a standard industry test method pioneered by Allied Signal (now part of Honeywell, Morristown, N.J.). The 16-shot test sequence progressively subjects armor material to ballistic impacts beyond its rated capacity to determine its ultimate protection effectiveness. Material replacement of this magnitude, according to Innegrity CEO Brian Morin, would reduce the cost of wearable armor to about $12/ft², compared to $20/ft² for vests made of 100 percent aramid. Innegrity, he says, manufactures HMPP via a melt extrusion process that produces a polymer with 80 percent crystallinity, compared to 50 percent crystallinity for standard PP. The crystallized structure, which runs perpendicular to fiber orientation, reportedly imparts tenacity of 9 grams per denier (g/d) and a toughness of 0.6 g/d, compared to 3.5 and 0.3 g/d, respectively, for glass, and 23 and 0.3 g/d for aramid.
DSM Dyneema LLC (Stanley, N.C.) focused on the U.S. Army’s Enhanced Combat Helmet (ECH), which is scheduled to be in service in 2009 and must have 25 percent improved fragmentation performance compared to the previous-generation aramid-fiber-based Advanced Combat Helmet. The ECH also must provide 7.62-mm small-arms protection. DSM Dyneema is working with the military on a possible solution involving the company’s Dyneema HB26 ultrahigh-molecular weight polyethylene fiber. James Thagard, DSM’s applications manager, life protection, said helmets made of HB26 meet ECH requirements and should meet flammability standards as well, without an outer skin of aramid or polybenzimidazole (PBI) fiber.
The U.S. government is moving toward a common regulatory regime for carbon nanotubes under the International Traffic in Arms Regulations (ITAR), reported Thomas Goldberg, CEO of ATS LLC (Washington, D.C.). ITAR regulations, administered by the Bureau of Industry and Security (BIS), aim to preserve U.S. technological and defense advantages by controlling technology exports. The emerging regulations are likely to apply to carbon nanotube production processes, such as thermal plasma synthesis, and specific hardware with nanotube content.
Malcolm Rosenow, business deve-lopment manager for AGY (Aiken, S.C.), provided an overview of the company’s new additions to its S-series product line (see “Learn More”). AGY’s S-1 Glass, he noted, has 30 percent higher pristine tensile strength, 19 percent higher modulus plus lower density and higher temperature resistance, compared to E-glass. Rosenow, who allowed that S-1 technically meets the specifications for structural high-strength glass (S-glass), contended that the AGY product was designed to fill the cost/performance gap between E-glass and AGY’s existing S-2 Glass, which was designed to fall between E-glass and carbon.
Owens Corning Composite Materials LLC’s (Toledo, Ohio) ShieldStrand fiber, introduced in 2007, is targeted to lightweight composite armor. David Hartman, research associate, composites solution business, said the material — which the company contends performs like an S-glass — will play a role in helping the military meet the U.S. Congressional order to up-armor more than 18,000 vehicles for greater protection. Hybrid armor designs that combine ShieldStrand with organic fibers can provide up to 30 percent weight savings compared to metal and as much as 50 percent cost savings versus S-glass or aramid, according to Hartman.