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Instabilities in Shape Memory Alloys and Structures

形状记忆合金和结构的不稳定性

基本信息

批准号：
1762389
负责人：
Stelios Kyriakides
金额：
$ 47.67万
依托单位：
University of Texas at Austin
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2018
资助国家：
美国
起止时间：
2018-09-15 至 2023-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1762389&HistoricalAwards=false
关键词：
Instabilities Shape Memory Alloys Structures

项目摘要

One of the most unique properties of shape memory alloys, like NiTi, is pseudoelasticity, which is the ability of the material to be deformed at room temperature to strains of a few percent and return to its unstrained configuration when unloaded. This unique characteristic is derived from a diffusionless transformation between two solid-state phases, which can be induced by changes in either stress or temperature. These characteristics are being exploited for novel structural applications in diverse fields; however, the design of shape memory structures is complicated by the: inhomogeneous deformations associated with the coexistence of the two phases during transformation, thermomechanical interactions, and significant tension-compression asymmetry. This project will use an integrated experimental-computational approach using material and structural samples to unravel these complications to enable the design and wider use of this unique class of materials. This project will progress the science of smart materials; advance the national health, prosperity, and welfare; and secure the national defense by enabling shape memory structural applications, like biomedical devices, aerospace components, damping and energy absorption, microelectromechanical systems, and morphing structures. In addition to the training of MS and PhD graduate students, the project includes undergraduate participation to attract them to research and graduate school. Outreach to K-12 students through lectures and laboratory demonstrations will be used to expand their interest in STEM subjects.Pure bending experiments on NiTi tubes have revealed complex interactions between the prevalent material nonlinearities with structural ones that lead to localization, collapse and failure. The proposed study has three main components: (i) Experiments on NiTi tubes loaded under bending, tension, compression, pressure, and torsion are planned in order to explore the results of these interactions and the associated limit states and provide a basis for developing the necessary analytical tools. (ii) A recently developed constitutive model framework that captures the tension-compression asymmetry and the inhomogeneous deformations associated with tensile stress states will be expanded to include thermal effects. The model will be calibrated using a spectrum of uniaxial, biaxial, and thermomechanical experiments. (iii) The constitutive model will be implemented in finite element models of the structures studied, testing their ability to reproduce the measured structural behaviors and the associated limit states. This multi-pronged approach to this class of problems involving interacting material and structural instabilities should provide the necessary tools for designing shape memory structures. The fundamental nature of this investigation is expected to also impact other materials that exhibit propagating instabilities like L?ders banding in steels, foams, and wood.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

形状记忆合金（如NiTi）最独特的特性之一是伪弹性，这是材料在室温下变形到百分之几的应变并在卸载时恢复到其未应变构型的能力。这种独特的特性来自于两个固态相之间的无扩散转变，这可以由应力或温度的变化引起。这些特性正在被开发用于不同领域的新型结构应用;然而，形状记忆结构的设计是复杂的：在转变过程中与两相共存相关的不均匀变形，热机械相互作用，以及显著的拉伸-压缩不对称性。该项目将使用材料和结构样本的综合实验计算方法来解决这些复杂问题，以实现这类独特材料的设计和更广泛的使用。该项目将推进智能材料科学;促进国家健康，繁荣和福利;并通过实现形状记忆结构应用，如生物医学设备，航空航天部件，阻尼和能量吸收，微机电系统和变形结构来保护国防。除了对硕士和博士研究生的培训外，该项目还包括本科生的参与，以吸引他们进入研究和研究生院。通过讲座和实验室演示，拓展K-12学生对STEM学科的兴趣。NiTi管的纯弯曲实验揭示了普遍存在的材料非线性与结构非线性之间的复杂相互作用，导致局部化，倒塌和失效。拟议的研究有三个主要组成部分：（i）计划在弯曲，拉伸，压缩，压力和扭转下加载NiTi管的实验，以探索这些相互作用的结果和相关的极限状态，并为开发必要的分析工具提供基础。(ii)一个最近开发的本构模型框架，捕捉的拉压不对称性和不均匀变形与拉伸应力状态将扩大到包括热效应。将使用单轴、双轴和热机械实验的谱来校准该模型。(iii)本构模型将在所研究结构的有限元模型中实施，测试其再现测量结构行为和相关极限状态的能力。这种多管齐下的方法，这类问题涉及相互作用的材料和结构的不稳定性，应提供必要的工具，设计形状记忆结构。这项调查的基本性质，预计也会影响其他材料表现出传播不稳定性，如L？该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。