Shape memory alloys (SMAs) have the unique ability to recover large deformations in response to thermal, mechanical, and/or magnetic stimuli. This behavior occurs by virtue of a crystallo-graphically reversible martensitic phase transformation between a high-symmetry parent austenite phase and a low-symmetry martensite phase. In general, when the material is deformed in the martensitic condition, the induced deformation can be recovered by applying a stimulus above certain magnitude (e.g., temperature, load, magnetic field), but as long as the critical transition point is not reached, it will retain the deformed condition indefinitely until actuated (e.g., heated). The innovation described herein utilizes the concept of shape setting a desired form that can be deformed and recovered upon the application of a stimulus. In this context, shape setting refers to the method of forming a SMA shape consisting of deforming the material into a form, constraining the material in all dimensions, heating to a certain temperature, holding isothermally for some period of time, and then cooling back to room temperature under the same dimensional constraint.
SMAs are routinely used to make actuator parts such as springs, beams, and other forms. The shape setting procedure is used to form these actuators. The concept uses SMAs to construct personalized forms (i.e., letters, symbols, words, characters, numbers, etc.) from a material feedstock (e.g., wire, tube, ribbon, etc.). The apparatus can be used to demonstrate the capability of these smart materials as part of instructional/educational materials, outreach, science kits, gifts, and other purposes. The proposed innovation will be a standalone apparatus containing all the necessary tools to create any shapes from the supplied kit without the need for additional tools or advanced knowledge in the art.
The concept employs SMAs in the form of wires, cables, tubes, or ribbons that are formed around modular pedestals of a predefined outline, followed by a specified heat treatment to form the desired shape. The formed shapes can then be distorted to an unrecognizable form, which can be recovered once exposed to a heat source, magnetic field, or upon load removal. The apparatus includes a method for setting the desired shape by selecting an outline, a constraint at both ends, a method for heating the element, control knobs and temperature monitors, and enclosures to house all the electronics and hardware.
The apparatus consists of a material feedstock in spools made of alloys that exhibit the shape memory effect (temperature-induced activation), superelasticity (stress-induced activation), and to some extent, magnetism (magnetically induced activation). The feedstock (e.g., wire spools) will be routed and positioned around an outline made by choosing the appropriate pins or pedestals with the desired form. Once formed, the first and last pins can be locked and connected to a heating circuit (e.g., joule heating, hot plate, heat gun). The circuit is comprised of control dials and indicators to ensure safe and accurate operation of the device. Before turning the heater on, a plastic shield is placed over the wire to protect the users. The final product will be a desired shape that can be deformed and recovered once activated. The apparatus will also include control logic to measure and control the temperature or current, timers, and lighting to indicate the process stages.
This work was done by Othmane Benafan of Glenn Research Center and Eunice Arvizu.
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