PRECISION INSTRUMENT FOR CHARACTERIZING CONTRACTION AND EXTENSION OF NITINOL WIRE

A large number of commercial applications could benefit from the properties of shape memory alloy (SMA) used in bias-spring actuators. These actuators often use nitinol wires that contract when heated above their transformation temperatures. During cooling, the wire relaxes and is elongated by a bias-spring. In this paper, we describe the conceptual and detailed design of a precision instrument to characterize the transient and steady-state contraction and relaxation of nitinol wires. Additional analyses of thermal and structural compliance conducted during the detailed design are presented. A variety of performance metrics such as the force, displacement, current and voltage can be determined using this instrument