Theoretical and Experimental Studies of Buckling Mechanics of 3D Thin Film/Shape Memory Polymer Systems

硬薄膜在软基板上的屈曲和起皱导致表面上有序的波浪图案。这种现象已被证明具有许多潜在的应用，例如在新型传感器和执行器，可拉伸电子，精密计量，光学光栅和能量收集装置中。形状记忆聚合物作为一类智能材料，可以记忆不同的形状，并可以通过加热等外部刺激从变形形状恢复到原始形状。当与薄膜屈曲相结合时，形状记忆聚合物的这些显著特征可以为在平面和复杂的3D结构上创建可控的表面图案提供独特的机会。该奖项支持形状记忆聚合物上薄膜屈曲的基本力学研究，并将开发由形状记忆聚合物和金属薄膜组成的3D混合材料系统的表面图案分析和制造策略。这项工作的结果将有利于表面工程、微/纳米机电系统和可拉伸电子设备在生物医学设备、机器人、智能电子和可部署系统中的应用。根据该奖项，PI将为研究生和本科生提供多学科培训，并将积极寻求代表性不足的群体和K-12学生的参与。近年来，薄膜在软基材上的屈曲力学一直受到力学界的关注，然而，目前的理论模型假设在屈曲和起皱形成过程中基材的力学性能不会发生显著变化。这一假设并不适用于形状记忆聚合物，它在热机械形状记忆周期中经历了巨大的性质变化。例如，模量通常变化两到三个数量级；粘度可以改变10到15个数量级。目的是结合理论和实验方法，在考虑不稳定过程中和与不稳定过程相关的大性质变化的情况下，为薄膜的屈曲和起皱力学发展一种新的理论。这将允许人们考虑薄膜在形状记忆聚合物上的屈曲过程，考虑时间、温度和机械性能变化的影响。研究了二维和三维形状记忆聚合物上薄膜带的屈曲，研究了屈曲模式随三维形状记忆聚合物结构演变的时间演变，为可编程器件提供了相关的四维屈曲系统。此外，本研究可为复杂三维混合材料系统的制造提供实用策略。

Buckling and wrinkling of stiff thin films on soft substrates results in ordered, wavy patterns on the surface. This phenomenon has been shown to have many potential applications, such as in novel sensors and actuators, stretchable electronics, precision metrology, optical gratings, and energy harvesting devices. Shape memory polymers, as a class of smart materials, can memorize distinct shapes, and can recover from the deformed shape to the original shape by external stimuli such as heating. These salient features of shape memory polymers, when combined with thin film buckling, can provide a unique opportunity for creating controllable surface patterns on planar as well as on complex 3D structures. This award supports research on the fundamental mechanics of thin film buckling on shape memory polymers, and will develop strategies for analysis and fabrication surface patterns in 3D hybrid material systems consisting of shape memory polymers and metallic thin films. The results from this work will benefit surface engineering, micro/nanoelectromechanical systems, and stretchable electronics with applications in biomedical devices, robotics, smart electronics, and deployable systems. Under the award the PI will provide multidisciplinary training to graduate and undergraduate students, and will actively seek participation from underrepresented groups and K-12 students. Buckling mechanics of thin films on soft substrates has been of interest to the mechanics community in the recent past, however, current theoretical models assume that the mechanical properties of the substrates do not change significantly during buckling and wrinkling formation. This assumption does not hold for shape memory polymers, which undergo dramatic property changes during a thermomechanical shape memory cycle. For example, the modulus typically changes by two to three orders of magnitude; viscosity can change by ten to fifteen orders of magnitude. The objective is to combine theoretical and experimental approaches to develop a new theory for the mechanics of buckling and wrinkling of thin films under consideration of large property changes during the and associated with the instability processes. This will allow one to consider buckling processes of thin films on shape memory polymers, with effects of time, temperature and changes of mechanical properties accounted for. Buckling of thin film ribbons on both 2D and 3D shape memory polymers will be studied The time evolution of buckling patterns coupled with the evolution of 3D shape memory polymer structures will be investigated, which will deliver 4D buckling systems of relevant to programmable devices. In addition, this research could provide practical strategies for fabricating complex 3D hybrid material systems.