HOWEVER much a shape-memory alloy is pulled and beaten about, a temperature change can push it back into its original form. But how does it remember what shape it should be?
One theory says the memory is stored by individual atoms, with each keeping tabs on its nearest neighbours. Another says that stresses in the structure store the information. Both explain the behaviour of nitinol, an alloy of nickel and titanium used in surgical instruments and spectacle frames. Nitinol has a “hot” form thought to be governed by structural memory, and a “cold” crystal form controlled by atomic memory.
But…
