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Characterization of a thin hard layer on a soft substrate---Theory and its application on a surface-modified PDMS.

机译：软基底上硬质薄层的表征-理论及其在表面改性PDMS上的应用

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摘要

This dissertation presents theoretical investigations to estimate the graded properties of a hard thin layer on a soft substrate. For this purpose, theoretical approaches have been made to explain experimental phenomena that can be observed in the surface-modified layer of PDMS.; A general strategy is presented, which can be used to determine the critical strain and the corresponding wave number for the wrinkling instability of a half space or thick layer loaded in compression, when the elastic properties vary with depth. Results exhibit dependence on modulus ratios similar to those observed when a homogeneous stiff surface layer is bonded to a more flexible substrate (i.e. where the elastic properties are piecewise constant).; Indentation theories are explored to explain the linear force-indentation depth relationships obtained from nanoindentation experiments. The plate theory and bi-layer system are considered as a theoretical model for the indentation problem at first. After examining the theory using the finite-element simulation, we conclude that the theory may not an adequate model for the indentation by a rigid indenter. A theoretical model is suggested, which considers the indentation into a half space with graded modulus by a rigid indenter. The force-indentation depth relationships very close to linear is obtained when the error function is used as a modulus function. Based on these results, we suggested an iterative method to determine the modulus of a surface-modified PDMS. The effect of residual strains is considered in the iterative method. With the residual strain, the method gives reasonable order of the modulus values.; We did two types of experiments to produce wrinkling in a modified-surface of PDMS. In each experiment, a discrepancy in the wavelengths is observed between the loading methods. To reveal this discrepancy, analytical models to describe the stress field in the system is suggested. The effect of Poisson's ratio mismatch, crack opening, and graded modulus is considered. While qualitative estimations for the discrepancy can be obtained with the effect of crack opening and graded modulus, quantitative estimations are not made in this research.
机译：本文提出了理论研究来估计软基底上的硬薄层的梯度性能。为此，已经采用了理论方法来解释可以在PDMS的表面改性层中观察到的实验现象。提出了一种通用策略，当弹性特性随深度变化时，该策略可用于确定压缩时加载的半空间或厚层的皱纹不稳定性的临界应变和相应的波数。结果显示出与模量比的依赖关系，该模量比类似于当均质的刚性表面层结合到更柔软的基底上时（即，弹性特性是分段恒定的）。探索压痕理论以解释从纳米压痕实验获得的线性力-压痕深度关系。首先将板理论和双层系统作为压痕问题的理论模型。在使用有限元模拟对理论进行考察之后，我们得出结论：该理论可能不适用于刚性压头的压痕模型。提出了一个理论模型，该模型考虑了通过刚性压头压入具有渐变模量的半空间。当将误差函数用作模量函数时，可以获得非常接近线性的力-压痕深度关系。基于这些结果，我们提出了一种迭代方法来确定表面改性PDMS的模量。在迭代方法中考虑了残余应变的影响。对于残余应变，该方法给出了模量值的合理顺序。我们进行了两种类型的实验，以在PDMS的改性表面上产生皱纹。在每个实验中，在加载方法之间观察到波长差异。为了揭示这种差异，建议使用分析模型来描述系统中的应力场。考虑了泊松比不匹配，裂缝开度和梯度模量的影响。虽然可以通过裂纹开度和梯度模量的影响获得差异的定性估计，但本研究并未进行定量估计。

著录项

  • 作者

    Lee, Dong Hee.;

  • 作者单位

    University of Michigan.;

  • 授予单位 University of Michigan.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2008
  • 页码 140 p.
  • 总页数 140
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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