Principle of memory alloy:
It is generally believed that shape recovery memory will occur when memory alloys change from complex rhombic crystal structure to simple cubic crystal structure. When the shape memory alloy is restored to its original shape, it is accompanied by a great force. The nitinol alloy is as high as 60 kg square mm, which is much greater than the force added during the initial deformation. Generally speaking, it can reach ten times of the original deformation, which means that the output energy is much larger than the input energy.
Scientists cannot explain this. Physicist Rosal said: "there is nothing wrong with the laws of thermodynamics, but these laws are not suitable for nitinol?". At present, many scholars believe that the reason why memory alloys can restore their original shape is due to the role of "memory factor". The "memory factor" is derived from the study of free energy and volume relationship in the phase transition process.
