Smart Materials
A Smart material is a material that can change its properties when there is a change in it’s environment. Examples of external stimuli that can change are: pH, temperature, stress, pressure, water content / moisture, light etc
Shape memory metals
A metal that ‘remembers’that it is meant to be a certain shape. The material can be easily bent (deformed) then under a reasonable temperature moves back to its original shape.
Smart memory metal are very useful because they are reliable (they do the same thing every time) and repeatable (we can do it over and over again).
The SCIENCE behind them:
Shape memory alloys have two crystal structures that the metal transfers between via a molecular rearrangement. In a molecular rearrangement, the solid state phase changes but molecules remain closely packed and therefore remain solid. The 2 phases are known as Martensite and Austenite.
The Martensite is soft and easily deformed.
You can see clearly the different crystal structures. When the Austenite cools its crystal structure changes This is known as the martensitic transformation.
Uses
All the things that we want to move once done with a motor or lever, we can now do with smart metals. These are low cost, low mass, smaller in size resulting in lower energy consumption.
Medicine – doctors use memory alloys to treat broken bones. The alloy is cooled then wrapped around the broken bone. Body temperature warms up the metal so it goes back to its original shape thus pulling the bone together and holding them in place while it heals.
The same thing happens for braces.
