高深宽比微纳层次结构仿壁虎脚毛参数优化设计
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摘要
壁虎可以在垂直墙面甚至天花板上自由爬行,他们和未知粗糙表面接触时,能产生牢固的粘附并轻易的脱附,这些特性在MEMS器件可拆卸安装和固定、爬壁机器人等领域有着极为广阔的应用前景。壁虎脚毛的分级层次结构,特别是其微米级刚毛/纳米级绒毛的高深宽比微纳层次结构,是保证壁虎脚毛既产生巨大粘附力又适应不同表面形貌的关键。为此本学位论文开展对壁虎脚毛精细分层结构各参数的优化设计。主要工作如下:
     建立微尺度接触的力学模型,解释了壁虎脚毛粘附机理;为了更接近实际情况,考虑表面粗糙度对粘附力的影响,建立了单根绒毛与粗糙表面接触模型,以及单层、双层以及三层粘附阵列与粗糙表面接触模型;进行接触全过程的粘附情况仿真,分析并总结了表面粗糙度、预载荷和结构刚度等因素对粘附能力的影响。
     分析壁虎脚毛的各种粘附特性,以及环境适应性要求,提出了强的粘附力、防纠结、防自断裂、快速脱附、较好的粗糙表面适应性等若干设计准则;采用自下而上的设计思想,建立了相应的力学模型;分析并总结约束模型中各参数变化对纤维半径、纤维长度、阵列占空比、阵列对称性、粘附力以及粘附功等参数的影响。
     综合考虑上述各约束条件,进行多目标多参数寻优求解,得到仿壁虎脚毛粘附结构的层次性几何特征(分形维数)、阵列几何特征(阵列密度、阵列对称性)以及单根接触几何特征(接触半径、深宽比、倾斜角)等设计参数。设计结果表明,优化设计得到的第一级结构的纤维半径、长度均在壁虎脚绒毛测量值范围内,第二级结构的纤维半径、长度也在壁虎脚刚毛测量值范围内,且具有更好的粘附能力。
Gecko has an extraordinary ability to maneuver on vertical walls and ceilings, for the adhesion is robust enough to function on unknown rough surfaces and also easily releasable on animal movement. The incredible characteristics have a very broad prospect of applications in the deployment and disassembly of MEMS devices, wall-climbing robots, etc. The multi-scale hierarchical structure of the gecko foot-hair, especially the high-aspect-ratio structure of its micro-scale seta and nano-scale spatulae is the critical factor of the gecko’s ability to adopt and stick to any different surface with powerful adhesion force. Accordingly, the optimal design mimicking the finely structured gecko foot-hair has been studied in this degree thesis. The main contents of this thesis comprise:
     Analyzing the micro-scale contact mechanics, reveal the mechanism of gecko adhesion. Considering the roughness, set up the contact models between one single spatula, one-, two-, muti-level adhesion arrays and rough surface respectively. Then simulate the adhesion ability through the whole attaching process with rough surfaces and analyze the influence of roughness, the applied force and the stiffness on the adhesion ability.
     Analyzing the properties of gecko adhesion at bumpy surfaces, introduce the enquired limitations and modeled to ensure the adhesion is robust and the release is easy, the fibrils are compliant enough to easily deform to mating surface’s roughness profile, yet rigid enough not to collapse under their own weight. And analyze the influence of these constraints to the parameters of optimal design.
     Based on these parameters, we have launched a bottom-up design methodology. A procedure is also developed here to find optimum designed parameters considering multi-object/parameter situations that adopt geometrical parameters of hierarchical dimensions (structure) with excellent patterns (density and symmetry) and sizes of single fiber (radius, length and angle). These results show that the optimal designed parameters of fiber structure sizes in both levels are in the scope of gecko spatulae and setae respectively and the simulated adhesion force at the second level is consistent with the observed value of single seta. These provided findings are the strong foundations of bio-inspired dry adhesives.
引文
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