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

形状记忆合金（SMA）是一种由两种或两种以上金属组成的材料，对施加的应力或温度变化具有弹性可逆响应的特性。sma主要有高温相和低温相奥氏体和马氏体。这些相产生了一种单向的热和机械转变，称为形状记忆效应（SME）。sma具有高功率重量比，这使得它们有效地用于驱动应用。然而，这种转换是非线性的，并且具有温度相关的滞后。此外，sma具有非常低的工作频率，40 Hz，随着频率的增加，工作输出下降。这是sma在驱动方面的最大缺点。这项研究将为实现更高频率输出和更小热滞后的最佳形状记忆合金结构和元件组合提供见解。这项研究将在宫崎博士在筑波大学的实验室进行，他专门研究sma的不同组合的生物相容性和拉伸特性。将开发特定元素组合（NiTi、NiTiNb和NiTiZr）的表征图，其中定义了位移与力、频率与功输出以及重量与功率密度的特性。这些合金，以棒状和薄片的形式，将在真空室中应用聚合物冷却方法来测试材料性能。不同的SMA结构（金属丝、薄板、管）的轮廓将决定表面积与冷却时间、力与位移、频率与驱动功输出的关系。本研究旨在完全了解sma的材料特性，从而确定最佳的元件组合，以实现低迟滞和提高带宽的总体目标。NSF EAPSI奖是与日本科学促进会合作资助的。

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.