Thermo-Mechanical Experiments and Modeling of Shape Memory Alloy Structural Elements

智能影响拟议的研究包括实验和建模工作，以表征形状记忆合金（SMA）结构元件的热机械行为。NiTi SMA具有独特的热机械性能，并且通常以细线或管的形式（例如，正畸线和动脉支架）展开，这些细线或管以弯曲、扭转或某种组合的方式加载。然而，在文献中可获得的此类实验的数量相对较少。PI最近对NiTi SMA的实验工作，使用光学和红外成像以及新的温度控制方案，有助于澄清自加热/冷却，机械不稳定性，应变和温度局部化以及相前沿传播所产生的问题。这些技术将在新的实验装置中扩展，以探测SMA元件在弯曲/扭转和柱屈曲下的结构行为。特别注意将支付材料级和结构级的不稳定性和变形和相变所产生的温度场之间的相互作用。这些实验将用于开发SMA空间棒的热机械模型和模拟工具，以计算易处理的方式捕获重要的热机械耦合和不稳定性。PI现有的热力学本构模型将适用于一个新的有限元，赋予轴向，弯曲和扭转自由度。这将是实施在一个有限元框架中的机械平衡和热方程同时解决，再加上内部场variables.Broader ImpactsThe希望的动力学定律的结果，拟议的研究将使更好地利用SMA材料在商业，工程和生物医学应用。实验数据和模拟工具将通过会议报告和期刊出版物广泛传播。更好地了解材料行为及其微妙之处以及模拟工具的可用性，应有助于工程师确定哪些应用程序可以适当利用材料的显着行为，并评估其性能。本提案教育部分的目的是提高本科生和研究生对这些非经典材料的认识。有趣的研究项目，自适应航空航天结构，使用SMA的独特能力将提供促进本科生的参与。许多拟议的研究将与个别监督的研究生进行。此外，与这种材料相关的理论和建模问题将通过介绍一个新的固体力学高级研究生课程来解决，题为“复杂材料的本构建模”。

Intellectual ImpactThe proposed research consists of experimental and modeling work to characterize the thermomechanical behavior of shape memory alloy (SMA) structural elements. NiTi SMAs possess unique thermomechanical properties and are often deployed in the form of thin wires or tubes (for example, orthodontic wire and arterial stents) that are loaded in bending, torsion, or some combination. However, the number of such experiments available in the literature is relatively few. The PI's recent experimental work on NiTi SMAs, using optical and infrared imaging and a new temperature control scheme, has helped to clarify issues arising from self-heating/cooling, mechanical instabilities, strain and temperature localization, and phase front propagation. These techniques will be extended in new experimental setups to probe the structural behavior of SMA elements under bending/torsion and column buckling. Special attention will be paid material-level and structural-level instabilities and to interactions between deformation and temperature fields arising from phase transformations. These experiments will be used to develop a thermomechanical model and simulation tool for SMA space rods that capture the important thermomechanical coupling and instabilities in a computationally tractable way. The PI's existing thermodynamic constitutive model will be adapted for a new finite element that is endowed with axial, bending, and torsional degrees of freedom. This will be implemented in a finite element framework where the mechanical equilibrium and heat equations are solved simultaneously, coupled with kinetic laws for internal field variables.Broader ImpactsThe hope is that the outcome of the proposed research will enable better use of SMA materials in commercial, engineering, and biomedical applications. The experimental data and simulation tools will be widely disseminated by conference presentations and journal publications. A better understanding of the material behavior and its subtleties and availability of simulation tools should help engineers determine which applications can make appropriate use of the material's remarkable behavior and to assess their performance. The intent of the educational portion of this proposal is to increase both undergraduate and graduate student's awareness of these non-classical materials. Interesting research projects for adaptive aerospace structures that use the unique capabilities of SMAs will be offered to foster undergraduate involvement. Much of the proposed research will be conducted with individually supervised graduate students. In addition, theoretical and modeling issues associated with such materials will be addressed by introducing a new advanced graduate course in solid mechanics entitled, "Constitutive Modeling of Complex Materials".