SMA shape memory alloys

Shaped activated carbons, 4 747 Shaped refractories, 6 491 Shaped-tube electrolytic machining (STEM), 9 599-600 Shape-memory alloys biomaterials, 3 741-750 Shape-memory alloys (SMAs), 22 339-354, 708t, 711-713, 721t applications of, 22 345-353 crystallography of, 22 341-345 ferrous, 22 342t future outlook for, 22 353 magnetically controlled, 22 712 nonferrous, 22 342t one-way, 22 712... 

Two-way shape-memory alloys (SMAs), 22 712. See also Virtual two-way SMA devices... 

A type of material known as shape memory alloy (SMA) can perform this trick. SMAs are more complicated than electrorheological fluids and the other smart materials previously described in this chapter. An SMA does not only react or respond to environmental conditions, it also has a memory that enables it to return to a specific structure, or sometimes switch between two different structures. After the material has been set, it can recover from a deformation that would be permanent in other materials. When the temperature is raised by an amount that depends on the specific material, it snaps back into shape automatically. The memory is based on phase transitions, as described in the sidebar on page 120. 

The use of shape-memory alloys as actuators depends on their use in the plastic martensitic phase that has been constrained within the structural device. Shape-memory alloys (SMAs) can be divided into three functional groups one-way SMAs, tw o-vvav SMAs, and magnetically controlled SMAs. The magnetically controlled SMAs show great potential as actuator materials for smart structures because they could provide rapid strokes with large amplitudes under precise control. The most extensively used conventional shape-memory alloys are the nickel-titanium- and copper-based alloys (see Shape-Memory Alloys). 

Shape Memory Alloys (SMAs) and Magnetostrictive Alloys... 

Recently, the integration of actuators into structures has also been researched. Shape Memory Alloys (SMA)-based actuators can be embedded into composites in the form of large diameter, plastically deformed wires. SMA are nickel/titanium alloys with a surprising property if plastically deformed at a low temperature (in a martensitic phase), they can recover the original shape and dimensions though heating above a definite temperature. When SMA are embedded and then heated, the restraints on free deformation imposed by the host composite originate a distributed stress which deforms the structure or modifies its vibrational response. 

In all application areas, a key material requirement is processability. Fabrication requirements can dominate in the choice of materials for MEMS. This restriction has kept shape memory alloys (SMAs), for example, from finding widespread application, although SMA MEMS devices have been demonstrated in the laboratory. 

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