The following chart gives rough guidelines for how much electrical current and force to expect with various wire sizes. If Flexinol® Actuator Wire is used within the guidelines, then obtaining repeatable motion from the wire for tens of millions of cycles is reasonable. If higher stresses or strains are imposed, then the memory strain is likely to slowly decrease and good motion may be obtained for only hundreds or a few thousand of cycles. The permanent deformation, which occurs in the wire during cycling, is heavily a function of the stress imposed and the temperature under which the actuator wire is operating. Flexinol® wire has been specially processed to minimize this effect, but if the stress is too great or the temperature too high some permanent strain will occur. Since temperature is directly related to current density passing through the wire, care should be taken to heat, but do not overheat, the actuator wire.
- 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. On small diameter wires (diameters less than or equal to 0.006" (0.15mm) diameter) currents which heat the wire in 1 second can typically be left on without over-heating it. Both heating and cooling can be dramatically changed (see section 3 of the technical characteristics at http://www.dynalloy.com//pdfs/TCF1140.pdf for more information.)
- Approximate cooling time, at room temperature in static air, using a vertical wire. The last 0.5% of deformation is not used in these approximations. LT = Low Temperature and HT = High Temperature Flexinol® Actuator wire.