NiTinol performance characterization and rotary actuator design

Abstract
The successful and practical application of shape memory alloy (SMA) torque tube actuators has frequently been hindered by an incomplete understanding of the effects of manufacturing and processing variables, particularly when working with large-scale systems producing high force and large displacements. Recently the authors have developed data for NiTinol SMA torque tubes subjected to a variety of processes routinely encountered in everyday industrial practice, with the objective of developing a robust and reliable high-energy actuator. Data are presented for more than 25 NiTinol torque tubes 5.5" long by 0.4" in diameter. The tubes were tested over a range of steady and variable loads exceeding 150 in-lbs of torque, with angular displacements of more than 60 degrees, and for durations exceeding 10,000 thermal cycles. Each tube's performance is characterized as a function of material source, level of cold work, heat treatment, tube fabrication technique, and training regime, and the results are shown. Changes in mechanical and shape memory property were also tracked, and they are reported. Application of NiTinol characteristics to practical design and fabrication of SMA actuators meeting a wide range of angular displacement and torque requirements will also be discussed.

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