Shape memory effect and Superelasticity

This presentation gives a brief introduction to the Shape Memory Effect and Superelasticity concepts, their working principle and their applications.

1. Shape Memory Effect and Superelasticity - Lalit B. Padekar

2. Shape Memory Effect It is the effect of restoring the original shape of plastically deformed material by heating it. This involves the Transformation of Detwinned (deformed) martensite to Austenite. The Phase transformation is mainly due to Heating. It takes place between Mf and Af

3. Superelasticity It is the ability of SMA to recover large strains (∼8%) with associated stress–strain hysteresis due to mechanical loading–unloading under isothermal conditions. It is an elastic (reversible) response to an applied stress, caused by a phase transformation between the austenitic and martensitic phases of a crystal. It takes place at temperatures above Af .

4. (Explanation in Notes)

5. Application of SME in bone Clamping

6. Application of Superelasticity Ni-Ti Alloy is used. Ni-Ti Alloy Af temperature can be programmed by varying alloying elements.

7. Braces Earlier, Aluminum wires were used. However, as the teeth started getting closer to their right alignment, the braces would loosen. This would result a periodic visit to your dentist for re-tightening. This was quite painful for the patient and quite tiresome for the Dentist. Now-a-days, the Ni-Ti wires are used instead of Aluminum. They are made in such a way that their Austenite temperature is similar to that of body temperature. Thus, when they are deformed and placed on the misaligned teeth, due to heating, the wires would try to go to their original shape. This would apply a constant pressure on teeth and there would never be a loose fit.

8. Spects Now, these are made popular by TITAN and are sold as TITANFLEX glasses. Basically, their frames are quite flexible. They can deform easily according to the contour of your skull thus giving you a great comfort. You can even fold them and fit them in your pockets. All you need to do is to heat them a little bit to get back their shape.

9. Thank You

10. References Design of Shape Memory Alloy (SMA ) Actuators by Ashwin Rao ,A.R . Srinivasa ,J.N . Reddy And of course, the Internet