Deforming Shape Memory Alloy Wire Using Continuous Axial Compression To Achieve Elongation On Heating

An innovative process for the continuous axial compression of a moving wire, US patent application No. 13/970,104, was used on NiTi alloy wire to axially shorten 1.2 mm diameter wire at a temperature of zero degrees C, below martinsite finish temperature, M_f. Then the wire was warmed to ambient temperature between the martensite start temperature, M_s and the austenite start temperature, A_s and retained its compressed length dimension.  Later, upon heating to 40 degrees C which is above the austenite finish temperature, A_f, the wire elongated instead of contracting as is the common shape change mode for NiTi alloy shape memory wire behavior.  The wire remains in the elongated, super-elastic state as long as its temperature remains above the martensite start temperature, M_s. The new continuous axial compression process for shame memory wire will be described along with the applications for shape memory alloy wire that has been processed using axial compression.  Since the axially compressed wire expands in length when actuated and performs with a pushing action, no tensile load carrying attachments are needed on the wire ends or within the device for operation. To prevent the wire from buckling due to compression stress, it can be easily confined with a single channel such as a covered groove.  Examples will be presented showing how the above important design features simplify force and/or motion application resulting in lower cost and more compact devices than can be achieved with the existing tensile mode of actuation.