Shape memory alloy fibers and shape memory polymer fibers and films and their composites for reversible shape changes
A plurality of reversible active composite materials are disclosed, including composites based on a shape memory alloy member (SMA) and a shape memory polymer member (SMP), as well as composites based on two different SMP members. Each different member (SMA or SMP) will be trained to remember a specific shape at a specific temperature. Where two different SMP members are employed, the members exhibit different glass transition temperatures. Such composite materials can be implemented in many form factors, including two generally planar members, a single generally planar SMP member with SMA fibers distributed throughout the SMP, and a SMA fiber/wire coated with a SMP coating. In particular, the SMA fiber/wire coated with a SMP layer can be used to form helical coils that can be used in paired hinges to achieve reversible bending of a structure into which such paired hinges are incorporated.
1. A structure that reversibly changes from a first configuration to a second configuration using paired composite hinges, the structure comprising:
(a) an upper face and a lower face;
(b) an upper hinge disposed adjacent the upper face; and
(c) a lower hinge disposed adjacent the lower face, the lower hinge being spaced apart from the upper hinge and being aligned with the upper hinge, each hinge comprising a SMA core and a SMP outer layer, where the SMA core has been trained to remember a first shape at a first temperature, and the SMP outer layer has been trained to remember a second shape at a second temperature, the first and second temperatures being different;
wherein the upper hinge is a coil centered on a first axis and the lower hinge is a coil centered on a second axis, wherein the first axis and the second axis are parallel.
2. The structure of claim 1 , wherein each hinge is configured such that the hinge is relatively larger at a temperature T Ex , and relatively smaller at a temperature T con .
3. The structure of claim 2 , wherein the structure comprises a plate, and the lower face achieves a convex configuration when the lower hinge is relatively larger than the upper hinge.
4. The structure of claim 2 , wherein the structure comprises a plate, and the lower face achieves a concave configuration when the lower hinge is relatively smaller than the upper hinge.
5. The structure of claim 1 , wherein a common axis aligning the upper hinge to the lower hinge is perpendicular to a portion of the upper face overlying the upper hinge and a portion of the lower face overlying the lower hinge.
6. The structure of claim 1 , wherein the first hinge and the second hinge are independently configured to be heated resistively by passing a current through the SMA core.
7. The structure of claim 6 , wherein the SMA core of each of the first hinge and the second hinge extends longitudinally beyond the SMP outer layer so as to provide electrical contacts for resistive heating.