Nonlinear Field-Coupling Responses of Adaptive Functionally Graded Structures

能够响应和适应各种外部刺激的复合材料自适应结构是多任务智能系统发展的重要要求。本研究的重点是表征自适应结构在高温、机械载荷和高电场作用下的非线性特性和性能。要研究的自适应复合结构由铁电陶瓷和金属成分组成，其组成和微观结构排列在厚度上连续变化-这种系统被称为功能梯度材料或fgm。非线性是由热电耦合效应引起的。例如，铁电陶瓷在高压应力和迟滞电场下可以发生极化开关。本研究的目的是利用粉末冶金方法制备自适应功能梯度复合材料；测试复合材料在不同的热-机电历史下，包括准静态、蠕变-松弛和滞后加载；建立了自适应结构在各种外界刺激下非线性响应预测和形状变化模拟的分析计算框架。对热-电-机械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导致的材料长期降解以及疲劳失效机制提供机会。这些研究活动将有助于多功能材料和结构的研究生课程发展，创造自适应结构形状变化的可视化和动画，并使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.