The 2014 Chevrolet Corvette will feature General Motors’ first production application of a shape-memory alloy (SMA)—a wire used to open and close the vent hatch that releases air from the car’s trunk area. The SMA wire, developed in-house by GM materials experts, replaces a motorized actuator and reduces component mass by approximately 1.1 lb (0.5 kg). GM vehicle engineers said use of the wire enables the trunk lid to close more easily than on the previous Corvette, where trapped air could make the lid harder to close.
SMAs typically are made of copper-aluminum-nickel (CuAlNi) alloys, nickel-titanium (NiTi) alloys, and copper-zinc-aluminum (CuZnAl) alloys. They’re considered “smart” materials because they can change their shape, strength, and/or stiffness when activated by heat (from electrical current, in the case of the Corvette), stress, a magnetic field, or electrical voltage. CuAlNi SMAs are much cheaper to make than NiTi alloys due to cheaper raw materials and less extensive processing. Their transformation temperatures—in the range of 80 to 200°C (176 to 392°F)—also are lower.
SMAs are being used increasingly in the medical and aerospace industries.They have “memory” and return to their original shape when deactivated. In the new Corvette, when activated the wire contracts and moves a lever arm to open the vent, allowing the trunk lid to close. Once the trunk lid is closed, the electrical current switches off, allowing the wire to cool and return to its normal shape, which shuts the vent to maintain cabin temperature.
Research for the SMA used on the Corvette began in late 2009, according to Paul Alexander, GM smart materials and structures researcher. He said GM has 247 patents in SMA technologies. GM Chief Technology Officer Jon Lauckner noted that SMAs enable new and improved features “at a lower cost than traditional motors and actuators.”
Lauckner and Alexander indicated that SMAs and other “smart” materials potentially could replace about 200 motorized movable parts on the typical vehicle, adding up to significant mass reduction.