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

形状记忆合金（SMA）是由两种或更多种金属组成的材料，其具有对施加的应力或温度变化的弹性可逆响应的特性。SMA具有两个主要相，高温相和低温相，分别为奥氏体和马氏体。这些相产生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，这使得它们对于驱动应用是有效的。然而，这种转变是非线性的，并具有温度依赖的滞后。此外，SMA具有非常低的工作频率，40 Hz，随着频率的增加，功输出下降。这是SMA在致动方面的最大缺点。本研究将提供最佳的形状记忆合金结构和元件组合的洞察力，以实现更高的频率输出与更小的热滞后。本研究将在筑波大学宫崎博士的实验室进行，宫崎博士专门研究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，并定义位移与力、频率与功输出以及重量与功率密度的特性。这些合金以棒和薄片的形式存在，将在真空室中采用聚合物冷却方法进行材料性能测试。还将制定不同SMA结构（线、薄板、管）的概要，这些SMA结构确定表面积与冷却时间、力与位移以及频率与驱动功输出的关系。本研究旨在全面了解SMA的材料特性，从而确定最佳元件组合，以实现低滞后和改善带宽的总体目标。这个NSF EAPSI奖是与日本科学促进协会合作资助的。

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.