By Neal Singer "Smart" wires have been embedded in a graphite-epoxy matrix similar to that used in fighter aircraft wings, providing the simplest means yet for changing a wing's shape to conform to different flight conditions, says the leader of a UI research team. The wires, created from a nickel-titanium alloy known as nitinol, are called smart because they "remember" two shapes and can be made to change into the shapes at different temperatures, said principal investigator Scott White, a UI aeronautical and astronautical engineer. Because the metal changes shape forcefully, the wires can, in effect, do the work of a motor. So far, researchers have used the wire's unique characteristics to activate levers and other machines. "This may be the first use for two-memory nitinol that does not require additional machinery," White said. "What we want is to have the embedded wires by themselves change the shape of the wing to match whatever the plane is doing, in order to achieve more efficient flight. A wing that uses the same shape for steady flight, rolls, takeoffs and landings one day may be considered primitive." The discovery that nitinol could remember two shapes was made in the late 1970s. Until now, embedding smart materials in a plastic matrix was problematic - because bubbles formed around the metal rods as the plastic set. Bubbles diminish the ability of the wires to change the shape of the plastic. Bubbles also encourage the growth of cracks in the matrix. White, however, found he could use a unique curing and surface pretreatment process to prevent bubbles from forming around the embedded wires. Training the wires after embedding them produced an unexpected bonus: It shortened the time it takes for the nitinol wires to "learn" what they're supposed to do, White said. "Ordinarily it takes 50 training cycles for the wires to remember their shapes." Encased in plastic, the wires were able to remember a shape after only a few training sessions. Nitinol is trained by by being stretched when cold, White said. The deformed metal is clamped so that it cannot move. It is heated, and then allowed to return to the original temperature of the training session, which may be approximately room temperature. The cycle is repeated a number of times. The repetition changes the crystalline structure of the wire and makes the lengthened nitinol a "remembered" state to which the composite will forcefully return at cold temperatures. At still higher temperatures, the metal will return to the shape it was in when first formed. The work builds upon research that began in 1959 with William J. Buehler's finding at the Naval Ordnance Laboratory in White Oak, Md., that nitinol had single-shape memory.