shape memory alloys

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“Shape memory alloys (SMA's) are metals, which exhibit two very unique properties, pseudo-elasticity, and the shape memory effect. Arne Olander first observed these unusual properties in 1938 (Oksuta and Wayman 1998), but not until the 1960's were any serious research advances made in the field of shape memory alloys. The most effective and widely used alloys include NiTi (Nickel - Titanium), CuZnAl, and CuAlNi.”


Meaning What
Shape Memory Alloys are Really Just a “smart” material that returns to it’s Normal shape and size after something like heat has manipulated it.

How does this work
The two unique properties described above are made possible through a solid state phase change, that is a molecular rearrangement, which occurs in the shape memory alloy. Typically when one thinks of a phase change a solid to liquid or liquid to gas change is the first idea that comes to mind. A solid state phase change is similar in that a molecular rearrangement is occurring, but the molecules remain closely packed so that the substance remains a solid. In most shape memory alloys, a temperature change of only about 10°C is necessary to initiate this phase change. The two phases, which occur in shape memory alloys, are Martensite, and Austenite. Martensite, is the relatively soft and easily deformed phase of shape memory alloys, which exists at lower temperatures. The molecular structure in this phase is twinned which is the configuration shown in the middle of Figure 2. Upon deformation this phase takes on the second form shown in Figure 2, on the right. Austenite, the stronger phase of shape memory alloys, occurs at higher temperatures. The shape of the Austenite structure is cubic, the structure shown on the left side of Figure 2. The un-deformed Martensite phase is the same size and shape as the cubic Austenite phase on a macroscopic scale, so that no change in size or shape is visible in shape memory alloys until the Martensite is deformed.”

A Typical use: The Smart Wing

The smart is a new technology that uses Shape memory alloys to Change the Shape of the Wing of a Plane to make it more maneuverable. This is done by simply sending a electric current throw the part of the plane to heat it to the desired temperature. This changes the shape of the wing making the Plane more maneuverable. This was previously done with a heavy Hydraulic system, thus significantly reducing the weight of the plane. This is demonstrated to the right.

Advantages:

Bio-compatibility
Diverse Fields of Application
Good Mechanical Properties (strong, corrosion resistant)

Limitations
expensive to manufacture
fatigue properties (twisting, bending, compressing)
Extreme Heat and cold
Must be a SMA
YOUR IMAGINATION