Effect of Inhomogeneous Deformation on the Response of Shape Memory Alloy Structures

形状记忆合金（SMA）越来越多地应用于阻尼和能量吸收、生物医学器件、MEMS、结构变形等领域。该项目的目标是研究sma中与应力诱导相变相关的局部变形对此类结构响应的作用。这些结构对弯曲、扭转和拉伸/压缩载荷的响应建模需要能够捕捉拉伸和压缩、多轴载荷和局部不均匀变形之间差异的材料模型。尽管现代本构模型可以捕获SMA行为的某些方面，但局部变形却不能。实验和分析的结合将用来弥补这一差距。简单SMA结构的实验，如管的弯曲、壳的轴向破碎和管簇的横向破碎，将用于说明局部变形如何改变结构响应。为了支持这种非线性的建模，将同时进行材料表征工作，以形成将缺失特征添加到本构模型的基础。这包括在不同温度和速率下测量材料在拉伸、压缩和双轴加载历史下的行为。结果将形成校准多尺度建模工作的基础，以包括鲁棒三维本构模型中缺失的特征。这些模型将依次在有限元模型中进行测试，以模拟结构实验。该项目涉及材料和结构不稳定性方面的实验专家和智能材料建模方面的理论专家之间的合作。这项合作将培养出受过广泛训练的研究人员，他们可以成为未来学术界和工业界多学科研究的领导者。本科生参与这个项目是为了吸引他们去读研。向高中学生进行实验室演示，其中包括大量的西班牙裔代表，以扩大他们对工程和科学的兴趣。

Shape memory alloys (SMA) like NiTi are increasingly being used in a range of applications including damping and energy absorption, biomedical devices, MEMS, morphing of structures, etc. The goal of this project is to study the role of localized deformations associated with stress induced phase transformation in SMAs on the response of such structures. Modeling the response of these structures to bending, torsion and tension/compression loadings requires material models capable of capturing differences between tension and compression, multiaxial loadings and the potential for localized inhomogeneous deformations. Although some aspects of SMA behavior can be captured by modern constitutive models, localized deformation is not. A combination of experiment and analysis will be used to bridge this gap. Experiments on simple SMA structures like bending of tubes, axial crushing of shells, and lateral crushing of clusters of tubes will be used to illustrate how localized deformations alter the structural response. To support the modeling of such nonlinearities a material characterization effort will be undertaken in parallel to form the basis of adding the missing features to constitutive models. This involves measuring the material behavior under tension, compression and biaxial loading histories at different temperatures and rates. The results will form the basis for calibrating a multi-scale modeling effort to include the missing features in robust three-dimensional constitutive models. The models will in turn be tested by implementing them in finite element models to simulate the structural experiments.The project involves a collaboration between an experimentalist expert on material and structural instabilities and a theorist expert on modeling of smart materials. The cooperation will generate broadly trained researchers who can become future leaders in multidisciplinary research in academia and industry. Undergraduate participation in the project is used to attract them to graduate school. Laboratory demonstrations to high-school pupils including a significant Hispanic representation are used to expand their interest in engineering and science.