Composite bats suitable for softball and less competitive baseball leagues have been around for years now. But adult baseball, with its high-hitting forces and tapered bat shape, has proven too tough for all-composite bat designs. Until now.
Last month, Easton Sports Inc. introduced its first all-composite bat designed to stand up to the rigors of adult baseball. The company makes these new Stealth Comp CNT bats from epoxy resin reinforced with Carbon Nanotubes (CNT). In the past, the company used CNT in bat handles, while crafting the barrel in a patented scandium alloy. With the Stealth Comp CNT, Easton extended composites all the way to the tip of the bat.
According to Matt Arndt, Easton's director of team sports products, these all-composite bats represent a big step forward in an evolutionary process that began about six years ago. That's when glass- and carbon-reinforced composites opened up new design possibilities that wouldn't have been possible with aluminum. "Aluminum doesn't give you a whole lot to play with from a design standpoint," Arndt says, noting that engineers could only look for stronger alloys and make very limited adjustments to wall thickness.
With composites though, Easton's engineers could vary the resin system, lay-up angles, and localize wall thicknesses to optimize bat performance within the rules set by the governing bodies for the various baseball and softball leagues. These rules limit a bat's overall weight and the barrel's "trampoline effect," or coefficient of restitution. Yet composites allowed Easton engineers to better balance the weight along the bat's length. They also leveraged the anisotropic mechanical properties of composites to widen the bat's sweet spot — or the portion that offers the maximum allowable trampoline effect. (see graph)
Despite these advantages, composite bats have traditionally suffered from durability problems that limited their acceptance in adult baseball. "Softball bats have a straighter barrel shape that's somewhat easier to produce in composites," Arndt says. In baseball, though, the tapered shape of the bat and the high-hitting forces sometimes did in composite bats before their time. "The real trick has been maintaining the performance advantages of composites while improving their durability," Arndt says.
And here's where Carbon Nanotubes come in handy. Carbon Nanotubes do have great tensile strength — about 150 GPa for the type Easton uses. But the real secret to their success in this application has to do with how well these tiny additives (less than 10 nanometers in diameter) disperse within the epoxy base resin. Arndt explains that failure analysis of previous composite bats showed they primarily come apart in areas where the resin matrix lacks adequate reinforcements — which in essence is a dispersion problem.
So Easton worked with Zyvex Corp., a company whose expertise includes dispersing CNT within a polymer matrix. According to Mark Bonash, Zyvex's production and quality director, a proprietary surface treatment promotes good dispersion — by keeping the nano tubes from clumping and ultimately by allowing them to bond to the polymer matrix. "Our technology acts as a bridge between the nanotube and the polymer," he says.
CNT materials also work hard in other Easton Sports products. Arndt says they've been applied to hockey stick blades and are being considered for use in the shafts, as well. For more information, visit http://rbi.ims.ca/4924-508. For more information on Zyvex, go to http://rbi.ims.ca/4924-509.
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