形状记忆聚合物表面的薄膜失稳和失效研究

Shape memory polymers (SMPs), as a type of smart material, can remember distinct shapes. In contrast to the traditional thin film/PDMS systems, shape memory polymers (SMPs) are capable of fixing strain/deformation without any external load, and therefore can be used in many interesting applications. The mechanical properties of SMPs vary greatly as SMPs deform, which leads to buckling mechanisms that are not well understood. In addition, no theories have been established to describe the structural defects in film/SMP systems (e.g., cracking and partial delamination) observed in experiments.. In this project, comprehensive studies of theoretical analysis, experimental investigations and numerical simulations will be conducted to tackle these challenging problems. A theoretical model will be established to analyze the buckling mechanisms of thin films on SMP substrates. The effects of temperature, the thermo-mechanical behaviors of SMPs and the plastic deformation of the thin films will be taken into account. The expression of total potential energy of the system will be given. On the basis of sub-region generalized variational principles, Euler equations and natural boundary conditions can be derived, from which the critical criterion of buckling and the analytical expressions of the wavelength and amplitude will be obtained. In addition, the failure of thin film/SMP systems, such as thin film fracturing and interfacial delamination, will be studied. Both the force method based on the Principle of Minimum Complementary Energy and the displacement method based on the method of separation of variables will be adopted to build a two-dimensional shear-lag model, based on which the fracturing criterion will be established. The driving-force and the resistance of delamination propagation will be studied by both theoretical modeling and experiments. The key parameters and the maximum resistance of delamination can be determined, and then the criterion of delamination will be established.. This research has both scientific significance and practical values.

作为一种智能材料，形状记忆聚合物（SMPs）可以记忆不同的形状。相比传统的薄膜/PDMS系统，SMPs可在无外力的情形下保持特定的应变，因此具有广泛的应用前景。截至目前，变形过程中SMPs力学性能的变化对屈曲机制的影响尚不清楚，对于实验中观察到的结构缺陷（如开裂和部分分层），尚无可靠的研究结论。.本项目旨在通过理论、实验和数值模拟相结合的方法，研究SMPs表面薄膜的失稳机理。考虑温度变化、SMPs的热力学行为和薄膜的塑性变形，给出系统总势能的表达式，采用分区广义变分原理，导出欧拉方程和自然边界条件，确定失稳的临界条件和波形特征的解析解；采用余能原理力法和分离变量位移法两种方法，构造薄膜/SMP系统的二维剪滞模型，建立起裂失效判据；采用实验与理论结合的方法研究分层扩展驱动力与扩展阻抗力。将二者结合确定分层时的临界分层参数与最大阻力，建立分层失效判据。本课题的研究具有重要的科学意义和应用价值。

作为一种智能材料，形状记忆聚合物（SMP）可以记忆不同的形状。相比传统的薄膜/PDMS系统，SMP可在无外力的情形下保持特定的应变，因此具有广泛的应用前景。.对于形状记忆聚合物（SMP）基底和弹性薄膜组成的双层结构，首先通过实验方法，在SMP表面上得到了均匀的、正弦波形的硅带和金带，结合一维SMP应变恢复函数，利用柔性基底表面薄膜屈曲波形参数（波幅、波长等）表达式，求解得到了在SMP基底收缩的过程中，弹性薄膜的屈曲波形随时间的变化规律。进而利用屈曲波形测量方法，探究了在一定范围内薄膜弹性模量与厚度的关系。.基于最小势能原理，建立了理论模型，得到了褶皱模式的波长和振幅，并从理论上分析了基底厚度的影响。当基底厚度是薄膜厚度的200倍以上时，本研究的结果与无限基底厚度模型的结果吻合良好。对于较薄的基底，基底厚度的影响变得很重要。该模型准确地描述了有限厚度基底对表面薄膜屈曲的影响，为可拉伸电子器件等未来薄膜基体系统的设计提供了重要的指导。.采用余能原理的力法和分离变量的位移法两种方法，建立了能准确描述薄膜/SMP结构特点的二维剪滞模型。该模型能够准确分析结构的正应力分布，很好地解释了周期性裂纹的形成机理。系统地讨论了几何参数和材料参数的影响，分析结果与有限元分析结果吻合较好，裂缝间距的预测与文献中的实验结果也较好吻合。最后构建了薄膜-基体双层结构的界面分层力学模型，确定了引起界面分层的剪切应力，并系统地讨论了几何参数和材料参数的影响。研究成体果可为基底-薄膜结构的起裂与分层等失效问题提供理论依据。