DoITPoMS


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Introduction

This LDP concerns the shape memory effect. This is a relatively complex effect, which is associated with shape changes being effected via martensitic (shear) phase transformations. Since they occur via the systematic, simultaneous displacement of large numbers of atoms, all of which retain the same neighbouring atoms (albeit in a slightly different configuration), there is potential for such shape changes to be reversed, provided the phase change can be reversed. This is most commonly achieved via a change in temperature, which affects the relative thermodynamic stability of the two phases. The actual demonstration, involving plastic deformation of a spring, which is subsequently reversed by simply heating with a hair dryer, is quick and easy to carry out. It's probably worthwhile, however, to also show some illustrations of the phase changes on an atomic scale. An IT resource is included in this package for exploring the crystal structures involved in the actual alloy used in the demonstration, which is Ni-50Ti. A brief explanation is also included of the "training" process that defines the "preferred" shape of the specimen.

It may be noted that there is a TLP focussed on the shape memory effect, accessible at https://www.doitpoms.ac.uk/tlplib/superelasticity/index.php. It may be helpful to have a look at this resource beforehand.


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