Shape Memory Alloys (SMAs) are a unique class of metal alloys that can recover apparent permanent strains when they are heated above a certain temperature. The SMAs have two stable phases - the high-temperature phase, called austenite and the low-temperature phase, called martensite. In addition, the martensite can be in one of two forms: twinned and detwinned, as shown in Figure 1. A phase transformation which occurs between these two phases upon heating/cooling is the basis for the unique properties of the SMAs. The key effects of SMAs associated with the phase transformation are pseudoelasticity and shape memory effect.
2 States
Austenite
-High temperature phase
-Cubic crystal structure
Martensite
-Low temperature phase
-Monoclinic crystal structure
When the material cools it goes into its Martensite(twinned)form. When heated it returns back to it's austenite form.
When a load is applied at low temperatures to the twinned form the material becomes detwinned. When heat is applied to the detwinned form it will revert back to the austenite form.
Shape Memory Alloy engine
