Shape memory alloys
Shape memory alloys or SMA as these are popularly known are alloys that undergo a phase transformation as they are heated or cooled. Therefore, the microscopic change is one in crystal structure whereas the macroscopic change is one in shape and/or length (this occurs in presence of applied forces). There is a phenomenon known as the two-way memory effect where the macroscopic change can be seen in absence of applied forces. A very popular shape memory alloy is Nickel-Titanium (or Nitinol). If you are not familiar with what a SMA can do, click on the DEMO. The change is reversible, although with quite a bit of hysteresis. Shape memory alloys are capable of undergoing significant changes in length against pretty high forces. Research on potential applications are wide ranging biomedical (catheters and orthodontics), process industries (valves and couplings) and aerospace (actuation of trailing edge flaps of aircraft wings or airfoils).
One of the significant disadvantages is that most SMAs operate at moderate temperatures (about 60 deg C or 140 deg F or thereabouts). Many applications (aircraft sitting out on a tarmac on a hot day) need actuation temperatures of 100 - 150 deg C (or 212 - 302 deg F). Our focus is on high temperature shape memory alloys, and to demonstrate that (i) these can undergo controlled actuation in a high temperature environment, (ii) these can undergo fast actuation in a moderate temperature environment.