Nonlinear Field-Coupling Responses of Adaptive Functionally Graded Structures

由复合材料制成的能够响应和适应各种外界刺激的自适应结构正吸引着多任务智能系统的发展。本研究主要研究自适应结构在高温、机械载荷和强电场作用下的非线性特性和性能。将要研究的自适应复合结构由铁电陶瓷和金属组成，其组成和微结构排列随着厚度连续变化-这样的系统被称为功能梯度材料或功能梯度材料。这种非线性是由热-机-电耦合效应引起的。例如，铁电陶瓷可以在高压应力和磁滞电场下经历极化开关。本研究的目标是利用粉末冶金方法制造自适应功能梯度复合材料；测试不同热-机电历史条件下的复合材料样品，包括准静态、蠕变-松弛和滞后加载；建立一个分析和计算框架，以预测非线性响应和模拟自适应结构在各种外界刺激下的形状变化。热力-机电耦合效应的研究将为进一步探索智能结构中由于氧化和老化引起的长期材料退化和疲劳失效机制提供机会。这些研究活动将有助于开发多功能材料和结构的研究生课程，创建适应结构形状变化的可视化和动画，并让本科生和研究生以及高中教师参与科学研究。分析工具和表征方法可以通过降低材料表征要求的成本和工作量，使许多制造和使用由自适应复合材料制成的设备的行业受益。

Adaptive structures made of composite materials that can respond and adapt to various external stimuli are appealing for the development of multi-tasking intelligent systems. This study focuses on characterizing nonlinear properties and understanding performance of adaptive structures subjected to elevated temperatures, mechanical loading, and high electric field. The adaptive composite structures to be studied consist of ferroelectric ceramic and metal constituents whose compositions and micro-structural arrangements vary continuously through the thickness - such systems are known as functionally graded materials or FGMs. The nonlinearity is due to thermo-electro-mechanical coupling effects. For example, ferroelectric ceramics can experience polarization switching under high compressive stresses and hysteresis electric fields. The objectives of this investigation are to manufacture adaptive functionally graded composites using a powder metallurgy method; test the composite samples at different thermo-electro-mechanical histories, including quasi-static, creep-relaxation, and hysteresis loading; and establish an analytical and computational framework for predicting nonlinear response and simulating shape changes in adaptive structures in response to various external stimuli.An investigation of the thermo-electro-mechanical coupling effects will open an opportunity to further explore long-term material degradation due to oxidation and aging, and fatigue failure mechanisms in intelligent structures. These research activities will contribute to a graduate course development in multifunctional materials and structures, creating visualization and animation of shape changes in adaptive structures, and involving undergraduate and graduate students as well as high school teachers in scientific research. The analysis tools and characterization methods can benefit many industries that manufacture and use devices made from adaptive composite materials, by reducing cost and effort in material characterization requirements.