EAPSI: Material property character mapping of shape memory alloy to improve actuation frequency output

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A shape memory alloy (SMA) is a material that consists of two or more metals with the property of an elastic-reversible response to an applied stress or temperature change. SMAs have two main phases, a high temperature and low temperature phase, austenite and martenite, respectively. These phases create a one-way thermal and mechanical transformation called the shape memory effect (SME). SMAs have a high power to weight ratio, which makes them effective for actuation applications. However, this transformation is non-linear and has a temperature-dependent hysteresis. Additionally, SMAs have a very low working frequency, 40 Hz, with a declining work output as frequency increases. This is the largest drawback for SMAs in actuation. This research will give insight to the best possible shape memory alloy structural and element combination for achieving a higher frequency output with a smaller thermal hysteresis. This research will be conducted at Dr. Miyazaki's lab at the University of Tsukuba, who specializes in studying the different combinations of SMAs for biocompatibility and tensile characteristics.A characterization map of specific element combinations (NiTi, NiTiNb, and NiTiZr) with defining properties of displacement vs. force, frequency vs. work output, and weight vs. power density will be developed. The alloys, in the form of rods and thin sheets, will be tested for material properties while applying polymer-cooling methods in a vacuum chamber. An outline of the different SMA structures (wire, thin sheet, tube) that determine the relations of surface area vs. cooling time, force vs. displacement, and frequency vs. work output for actuation will be developed as well. This study is looking to completely understanding the material properties of the SMAs and therefore possible to determine the best element combination to achieve the overall goal of low hysteresis and improved bandwidth. This NSF EAPSI award is funded in collaboration with the Japan Society for the Promotion of Science.