Precision instrument for characterizing shape memory alloy wires in bias spring actuation

Abstract

Some metallic alloys such as Nitinol ͑NiTi͒ exhibit the shape memory effect, which is suitable for generating force and displacement when the alloy changes phase during a heating and cooling cycle. These shape memory alloys are often formed into one-dimensional wires, tubes, and ribbons that are preloaded by bias springs to create inexpensive actuators for electromechanical devices. This article describes a new instrument for measuring the quasistatic characteristics of the alloy and the transient performance of bias-spring actuators when resistively heated and convectively cooled. The instrument achieves more accurate measurements by eliminating rolling friction and by sensing force and displacement in line with the bias spring and shape memory alloy wire. Data from the instrument enables calculation of stress and strain at constant temperatures and during actuation cycles.

An accurate self-sensing method for the control of shape memory alloy actuated flexures

“…The same results have been observed in Ref. [22]. The force drop is likely to be caused by the SMA internal friction, when the crystallographic movement changes direction.…”

Wrinkling control of inflatable booms using smart material patch

“…The test specimen is Flexinol, commercial SMA wire actuator produced by Dynalloy Inc. [14], with the dimensions of φ 0.152X240mm. When the electric current through the wire is increased gradually, the strain and contraction force shows increase stepwise as expected [15]. Strain and critical current at which strain of SMA wire steps up are observed by laser sensor.…”

Design of a novel flexible shape memory alloy actuator with multilayer tubular structure for easy integration into a confined space

“…The basic mechanism of the SMA actuator is quite simple, whereby the material can be readily deformed by applying an external force under the martensite transformation finish temperature, and will recover its original shape when heated beyond the austenite transformation start temperature. Heating methods include inductive heating, Joule heating, mechanical heating, light heating, etc [19].…”