Structural behavior of SMA composite beams

Shape memory alloy (SMA) composites are one class of adaptive materials in which SMA wires are embedded in a polymer matrix composite material. By selectively activating the SMA wires, the beam shape can be controlled or `adapted' to different loading conditions. For instance, an adaptive beam could be used as a torque box for an aircraft wing where coupled bending-twisting behavior may be desirable. SMA composite beams have been manufactured and mechanically tested under static loading conditions. Nitinol (SMA) wires composed of 55% nickel and 45% titanium were trained and tested to determine the transformation temperatures. A two way shape memory (TWSM) was trained into the wires. Once trained, the wires undergo a reversible phase transformation from martensite to austenite as the temperature is increased. This transformation leads to shape recovery and associated recovery strains. These recovery strains are used to apply forces which deflect the SMA beams during static actuation. Their structural behavior is correlated using simple beam theory. Thermal effects during actuation are shown to have a major influence on structural behavior.