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The following figures and information show a part of the investigations concerning SMA springs. Different SMA springs have been produced an tested for several companies.

This two images indicate the load-deformation-behaviour of two different SMA spring with different diameters and transition temperatures. At high temperatures (here 100°C) the spring acts like an ordinary steel spring, but at low temperatures (here 23°C) the spring yields at a constant load.

The figure shows the load-deformation behaviour of a SMA spring at different temperatures. At 20°C and 30°C the spring is martensitic and does not return into its orginal length. Above 30°C the spring is austenitic but martensite is formed by load-induced phase transition and returns to austenite upon decreasing load. The higher the temperature is, the lesser martensite is formed an therefore the spring gets stiffer.

The following figure demonstrates the behaviour of a SMA spring at two different temperatures(20°C and 100°C) and an ordinary steel spring. If the parameters of the springs are chosen like in this example, the steel spring is capable of compressing the SMA spring at low temperature. On the other hand ,the SMA spring may compress the steel spring at high temperature. 

It is possible to produce the SMA spring in order to perform the compression of the steel spring at a desired temperature. Therefore the SMA spring may simultaneously act as an actuator and as a sensor.