Selecting Suitable Shape Memory Alloys

Shape memory alloys are materials that can recall and return to their original shape after they are distorted. This is normally done when heat gets applied to the bent alloy causing its reversion back to whatever shape it held before. This is because the alloys, copper-aluminium-nickel and nickel titanium, have two different crystal structures that they can take on. The heat forces the reversible change in the crystal structure to occur and the material only has one valid motion to move through, that of the unbending. The concept of hysteresis is also important. When a piece of elastic is stretched it stores elastic potential energy, but when it returns to normal length some of the energy has been lost. This is not just the normal energy loss that is to be expected in any transfer, sometimes up to half the energy can be turned into heat on the return.

Since these alloys are pseudoelastic and have the sole purpose of being stretched; hysteresis can become a serious problem. But a new mix of shape memory alloy has been made, titanium-lead-chromium, with an exceptionally small hysteresis value being about 10 kelvin, less than any other known shape memory alloy. It also has a very high transformation temperature having to reach over 650 kelvin before to reverting back to its original shape. The combination of these unique properties makes this material very interesting; but what is even more interesting is the method they used to find it. Using numerical simulations and strict sampling methods is how this new alloy was found and the methodology can be used in the future to create any number of advance materials for a wide range of uses.


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