多尺度粗糙表面的MEMS涂层黏着接触力学研究

Because of the size effect and surface effect, the adhesive force and multi-scale roughness of coating surfaces for MEMS become the significant factors which influence the contact characteristics. However, these two factors have not been included simultaneously in the existing contact models for coatings, which were difficult to reasonably elucidate the contact behaviors at the micro and nano scales of coating surfaces for MEMS. This project intends to undertake the following studies. (1) An adhesive contact model of coatings at the asperity level will be established considering the molecular interaction inside the material, and an equivalent Tabor parameter will then be derived. Furthermore, the adhesion-induced snapping phenomenon and the formulae for the interfacial force and contact radius with the separation distance between surfaces will be studied. (2) An adhesive contact model of coatings with multi-scale rough surfaces will be developed by combining the fractal geometry characterization of multi-scale rough surfaces and the adhesive contact theory of coatings at a single asperity level. An expression for adhesion index will be derived and the influence of multi-scale roughness and layered material properities on the adhesive contact behaviors will be revealled. (3) The surface topography of coatings will be measured by the atomic force microscope, and the fractal parameters will be obtained from the power spectrum. Also, the force-displacement curve will be obtained from AFM experiment in order to validate the contact model of multi-scale rough surfaces. (4) The delamination model of the coating/substrate interface under adhesive contact at the micro and nano scales will be developed so that the influence of adhesion effect on the interfacial delamination will be illustrated. The objective of this project are to provide the key theoretical basis of reliably design for MEMS coatings.

由于尺度效应和表面效应的作用，MEMS涂层接触表面的黏着力和多尺度粗糙度成为影响其接触性能的重要因素。然而现有涂层接触模型没有同时考虑上述因素，难以合理解释MEMS涂层表面微/纳尺度下的接触行为。本项目拟开展如下研究：（1）考虑材料原子之间相互作用建立涂层单峰黏着接触模型，推导等效Tabor参数，研究由黏着引起的突跳现象及界面力和接触半径与表面分离距离的关系。（2）将上述单峰黏着接触模型与多尺度粗糙表面的分形几何表征耦合，建立多尺度粗糙表面的涂层黏着接触模型，获得黏着参数表达式，揭示多尺度粗糙度和层状材料特性对涂层黏着接触行为的影响。（3）采用原子力显微镜测量涂层表面形貌，由功率谱图获得分形参数，测量力-位移曲线，对多尺度粗糙表面黏着接触模型进行验证。（4）构建微/纳尺度黏着接触下涂层/基体界面的分层模型，阐释黏着作用对界面分层失效的影响机制。本研究将为MEMS涂层可靠性设计提供理论依据。

由于尺度效应和表面效应的作用，MEMS涂层接触表面的黏着力和多尺度粗糙度成为影响其接触性能的重要因素。然而传统黏着接触理论无法考虑物体内部分子间的相互作用以及材料非均质等因素，难以预测MEMS涂层表面微/纳尺度下的黏着接触行为。本项目以影响MEMS稳定性、可靠性以及使用寿命的黏着接触问题为研究背景，开展了如下研究：（1）MEMS涂层的单峰黏着接触力学研究。以Hamaker求和法和分子间的Lennard-Jones相互作用势为基础，推导了包含微球尺度参数以及涂层和基体表面能参数的等效黏附接触压力方程，建立了MEMS涂层广义单峰黏着接触力学模型；构建了考虑尺度效应并给出发生突跳时接近距离的黏附图，拓宽了国际上已发表的黏着图的尺度适用范围。（2）多尺度粗糙表面的MEMS涂层黏着接触力学研究。将纳米级及微米级粗糙度分布引入到表面间距方程中，构建了刚性微球与多尺度粗糙表面的黏着接触模型，并通过双非精确牛顿法、二次共轭梯度稳定算法以及FFT快速算法进行了数值求解，发展了高效高精度的多尺度粗糙表面黏着接触力学的数值方法。（3）MEMS涂层/基体界面的分层失效研究。构建微/纳尺度黏着接触下涂层/基体界面的分层模型，阐释了黏着作用对界面分层失效的影响机制。结果表明：黏着接触下，涂层弹性模量对涂层/基底系统界面分层起始的影响随表面黏着作用强度的变化而变化。当黏着功较大时，涂层弹性模量的增加会降低界面分层产生的可能性；而黏着功较低时，则会提高涂层/基底系统界面分层产生的风险。（4）MEMS涂层的黏着接触实验研究。采用原子力显微镜测量涂层表面形貌及力-位移曲线，对多尺度粗糙表面黏着接触模型进行验证。结果表明：本项目所提出的理论模型能够很好预测MEMS涂层的黏着特性，为MEMS涂层减黏设计提供了理论依据。