Glossary of SMA

The    temperature at which the Martensite to Austenite transformation begins on    heating in a single stage transformation.

The    distance a spring can be stretched, or the angle a wire can be bent, without    permanent deformation; the useful, working range of a spring or wire.

A heat    treat process designed to remove the effects of cold work and/or aging heat    treatments.

The    high temperature phase of Nickel Titanium. In its austenitic phase, NiTi is    stiff and elastic and will immediately return to shape after bending. (See    Superelasticity.)  Austenitic NiTi wire    has the B2 body-centered cubic crystal structure.

The    Bend and Free Recovery test provides an analysis of bend angle to    temperature, and it can be used in determining As and Af temperatures of a    NiTi wire.

Springs    which are manufactured with open spaces between helixes. Compression springs    are typically used in applications were they are compressed to provide a    “pushing” force.

Differential    Scanning Calorimetry – a laboratory procedure used to identify the thermally    induced transformations of a particular alloy.

The    apparent ease with which a wire can be deflected without incurring permanent    deformation.

Springs    which are manufactured with closed coils, such that the helixes are wound    tightly together. Extension springs are typically used in tensile to provide    pulling forces.

The    difference in bending loads during loading and unloading in a test such as 3    Point Bending.

The    low temperature phase of Nickel Titanium. In its martensitic phase, Niti is    soft and bends easily. NiTi will stay in this state until exposed to heat    above its TTR. NiTi in its martensitic state is responsive to chilling, as it    becomes even softer and more easily bent. Martensitic NiTi has the B19    monoclinic crystal structure.

The    temperature above Af at which stress induced martensite will no longer form.    Typically =80°C above functional Af.

The    temperature at which the transformation from Austenite to Martensite is    completed on cooling a single stage transformation.

The    temperature at which the transformation from Austenite to Martensite begins    on cooling in a single stage transformation.

Usually    in reference to the angle or percentage that a wire or component does not    return to its original shape after being strained.

A    material’s ability to resist permanent deformation when bent.

An    apparent plastic deformation in the martensitic phase, which undergoes a    thermo-elastic change in the crystal structure when heated through its    transformation temperature range, resulting in a recovery of the deformation.    The ability for a preformed wire, below its TTR, to be deformed to some    degree and then, upon heating, to return to its original shape. Further    details are available on the Material    Characteristics page.

The    spontaneous phase change of the crystal lattice from Austenite to Martensite    as stress is applied to the material at a temperature above Af. Stress    Induced Martensite spontaneously reverts to Austenite as stress is removed,    unless permanent deformation has been introduced into the material.

A    nonlinear recoverable deformation behavior of Nickel Titanium shape memory    alloys at temperatures above Af. The nonlinear deformation arises from the    stress-induced formation of martensite on loading and the spontaneous    reversion of this crystal structure to austenite upon unloading. Further    details are available on the Material    Characteristics page.

When    stretched, the maximum force a wire can withstand without breaking.

Term    used for martensitic wire, as it is responsive to heat-activation. See    Martensite.

For    shape memory alloys, such as Nickel Titanium, a change of phase occurs, such    as from martensite to austenite, in a specific temperature range. The TTR is    adjustable by several means to produce desired characteristics.