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Thermomechanical modeling and analysis of flexible structures with shape memory alloy actuators.

机译：具有形状记忆合金执行器的柔性结构的热力学建模和分析。

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A flexible active structure with shape memory alloys (SMA) usually involves structural and material nonlinearities, as well as strong coupling between the structure and shape memory alloys. Both residual deformation and hysteresis phenomena observed are crucial issues that influence the behavior and the ability to control an active structure. Furthermore, since there is a shift of the material parameters of SMA during cyclic thermomechanical loading in service, the task to provide a realistic model upon which to base a design becomes extremely difficult. It is those challenges which motivated the work of this dissertation.; This dissertation focuses on the modeling and analysis of active structures with shape memory alloys and attacks the associated phenomena mentioned above. In the first part of the dissertation, a thermomechanical model is developed to predict the structural response of a flexible beam with SMA wire actuators. A nonlinear static analysis is first carried out to investigate the deformed shape of a flexible cantilever beam caused by an externally attached SMA wire which is actuated electrically. The actuation force applied by the SMA actuator to the beam is evaluated by solving a coupled problem that combines the thermodynamic constitutive model of SMA and the heat conduction response of SMA with the structural model of the beam. The proposed model is used to simulate the experimental results, thus demonstrating the feasibility of using SMA actuators for shape control of active flexible structural systems. Modelling of the response of the elastomeric rods with an embedded actuator under the influence of gravitational force is also investigated with a general theory of flexible rods and an approximate formula. Both formulations allow to account for different temperature histories of actuation for shape memory alloy actuators.; In the next part of the dissertation, an identification method for the material parameters of SMA is presented with the application of an optimization theory. The method allows the determination of the material parameters for the SMA actuator which is being used on the active structures.; To incorporate the observed phenomena of the residual deformation during cooling of SMA, a modified thermodynamic constitutive model of SMA is derived based on previous work by Boyd and Lagoudas (1994). An internal variable of martensite volume fraction is decomposed into two parts: self-accommodated and detwinned martensite. The dissipation potentials, derived from the second law of thermodynamics, are explicitly given in 1-D for the evolution of the volume fractions of martensite. The concept of the critical stresses is introduced into the constitutive model. A prototype structure example is used to demonstrate the ability to predict the residual deformation and the recovery stress, which can be used as a guidance in design.; Finally, a phenomenological model and example for minor hysteresis loops of SMA is presented and extended to predict the hysteresis outputs with multiple thermodynamic driving forces. The efforts of this dissertation provides a framework to serve for the structural application of shape memory alloys.
机译：具有形状记忆合金（SMA）的柔性有源结构通常涉及结构和材料的非线性，以及结构和形状记忆合金之间的强耦合。观察到的残余变形和滞后现象都是至关重要的问题，它们会影响行为和控制主动结构的能力。此外，由于在使用中的循环热机械加载过程中SMA的材料参数发生了变化，因此提供一种实际模型作为设计基础的任务变得极为困难。正是这些挑战激发了本论文的工作。本文主要研究形状记忆合金对活动结构的建模和分析，并针对上述相关现象进行研究。在论文的第一部分中，建立了一个热力学模型来预测带有SMA导线执行器的柔性梁的结构响应。首先进行非线性静态分析，以研究由外部电连接的SMA导线引起的柔性悬臂梁的变形形状。通过解决将SMA的热力学本构模型和SMA的热传导响应与梁的结构模型相结合的耦合问题，可以评估SMA致动器对梁施加的致动力。所提出的模型用于模拟实验结果，从而证明了使用SMA执行器进行主动柔性结构系统的形状控制的可行性。还使用挠性杆的一般理论和近似公式研究了具有嵌入式致动器的弹性杆在重力作用下的响应建模。两种配方都可以考虑形状记忆合金致动器的不同致动温度历史。在本文的下一部分，结合优化理论，提出了一种SMA材料参数的识别方法。该方法允许确定用于有源结构上的SMA致动器的材料参数。为了结合观察到的SMA冷却过程中残余变形的现象，在Boyd和Lagoudas（1994）的先前工作的基础上，得出了SMA的改进的热力学本构模型。马氏体体积分数的内部变量被分解为两部分：自适应的和解缠的马氏体。从热力学第二定律得出的耗散势在1-D中明确给出，用于马氏体体积分数的演变。临界应力的概念被引入到本构模型中。原型结构示例用于演示预测残余变形和恢复应力的能力，可作为设计指导。最后，给出了现象学模型和SMA较小滞后回线的示例，并将其扩展以预测具有多个热力学驱动力的滞后输出。本文的工作为形状记忆合金的结构应用提供了框架。

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