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

NiTi等形状记忆合金（SMA）越来越多地用于一系列应用，包括阻尼和能量吸收、生物医学设备、MEMS、结构变形等。该项目的目标是研究与应力相关的局部变形的作用。SMA中的相变对此类结构的响应。对这些结构对弯曲、扭转和拉伸/压缩载荷的响应进行建模需要能够捕获拉伸和压缩、多轴载荷之间的差异以及局部不均匀变形的可能性的材料模型。虽然SMA行为的某些方面可以被现代本构模型捕获，但局部变形却不能。实验和分析的结合将被用来弥合这一差距。简单的SMA结构，如弯曲的管，轴向破碎的壳，和横向破碎的集群管的实验将被用来说明如何改变局部变形的结构响应。为了支持这种非线性的建模，材料表征工作将并行进行，以形成将缺失的特征添加到本构模型的基础。这涉及在不同温度和速率下测量拉伸、压缩和双轴载荷历史下的材料行为。结果将形成校准多尺度建模工作的基础，以包括在强大的三维本构模型中缺失的功能。该项目涉及材料和结构不稳定性方面的实验专家与智能材料建模方面的理论专家之间的合作。这项合作将产生受过广泛培训的研究人员，他们可以成为学术界和工业界多学科研究的未来领导者。本科生参与该项目是为了吸引他们进入研究生院。实验室演示给高中学生，包括一个显着的西班牙裔代表被用来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.