FLEXINOL® Actuator Spring Technical and Design Data

Flexinol® actuator springs can be an alternative to straight Flexinol® actuator wires for applications with low force and high travel requirements. These springs can contract and relax multiples of their length. When Flexinol® actuator springs are used within the correct parameters high cycle life is expected. Pricing can be found clicking here, and adding crimps on the ends is also possible.


Stretch Ratio “SR” is defined as any length “L" over the solid length “SL", in any state, hot or cold. For example a spring with a SR of 4 cold and 2 hot, assuming a solid length “SL” of 10mm would then be 20mm hot, and 40mm cold.


While these values will vary depending on how the springs are used, are still a reasonable starting point for a design. In your calculations please reference the displacement per coil in conjunction with the stretch ratio to help identify the appropriate length spring to purchase. The following chart gives rough guidelines as to how much current and force to expect with various Flexinol® actuator spring.

Spring Wire Diameter in(mm), Outer Diameter in(mm)

SR Cold,
SR Hot*

Displacement / Coil in(mm)

Resistance on Straight Wire ohms/inch
Heating Pull Force**
Cooling Deformation Force** pounds
Approximate*** Current for 2 Seconds Contraction (A) Cooling Time 194° F, 90°C "HT" Wire**** (seconds)
0.020 (0.51),
0.136 (3.45)
16, 7 0.18 (4.6) 0.11 (4.33) 0.536 (243.3) 0.215 (97.32) 3.4 15.0
0.015 (0.381),
0.10 (2.54)
15, 6 0.14 (3.4) 0.21 (8.27) 0.307 (139.3) 0.122 (55.72) 1.9 9.0
0.008 (0.203),
0.054 (1.37)
14, 5 0.07 (1.8) 0.74 (29.13) 0.089 (39.3) 0.035 (15.94) 0.7 3.0

*The Stretch Ratio “SR” values are typically accurate, but remain approximate values.

** The Heating pull force is based on ~ 25,000 psi (172 MPa), which for many applications is the maximum safe stress for the wire. However, many applications use higher and lower stress levels. This depends on the specific conditions of a given design. The cooling deformation force is based on ~10,000 psi (70 MPa), which is a good starting point in a design. However, this value can also vary depending on how the material is used

*** The contraction time is directly related to current input. The figures used here are only approximate since room temperatures, air currents, and heat sinking of specific devices vary. Both heating and cooling can be dramatically changed (see section 3 of the technical characteristics at http://www.dynalloy.com/TCF1140.pdf for more information.)

**** Approximate cooling time, at room temperature in static air, using a vertical spring. The last 0.5% of deformation is not used in these approximations. HT = High Temperature Flexinol® Actuator Spring.