Interactive demonstrations and laboratories using shape memory alloys

Abstract

Shape memory alloys (SMAs) constitute a unique class of materials that undergo a reversible phase transformation allowing the material to display dramatic stress-induced and temperature-induced deformations that are recoverable. Nickel titanium (NiTi) is a shape memory alloy used in a wide variety of biomedical, aerospace, automotive and other applications. The austenite-martensite phase transformation that occurs in these alloys with changes in temperature or applied stress is responsible for the unique properties of this material. The unusual behavior of SMAs provides an exciting way to engage students and can be incorporated into a variety of courses under topics such as phase transformation behavior, constitutive relations, and smart materials and structures. Three modules that can be used as either demonstrations or experiments will be described. In the first, an apparatus for demonstrating the actuation abilities of NiTi SMA via an overhead projector has been created for classroom demonstrations using Dynalloy, Inc. components. The second experiment involves visualizing the latent heat of transformation during loading using a liquid crystal paint. In addition to exploring temperature-induced and stress-induced transformation, students can also get first-hand experience with the influence of heat treatment on this alloy in a laboratory environment. The third experiment uses an inexpensive training jig that allows students to shape set a piece of NiTi wire into any desired shape and see its shape memory abilities through subsequent deformation and heating.