考慮黏附效應及塗層硬度效應之橢圓粗糙表面接觸與磨擦行為分析

Contact and Friction Behavior of Ellipsoids Rough Surface with Adhesion and Coating Hardness Effect

陳進茂(Jin-Mao Chen)

指導教授 ： 洪政豪

國立虎尾科技大學/工程學院/機械與機電工程研究所/碩士(2008年)

摘要

大部分加工表面粗度具有加工工具的運動方向，以致在不同的方向上有不同的曲率半徑，非等向之橢圓波峰較接近實際粗糙表面。常見精密機械為減少接觸面之黏附與磨損現象，多於表面塗佈適當材料，以致元件硬度隨著厚度有所改變。本文利用表面形貌的碎形特性考慮橢圓率、塗層硬度效應、黏附力的碎形粗糙表面微接觸模式來研究界面間之接觸性能，並利用實驗以評述模式中需要的元件表面碎形及材料參數的求法，進行實例分析。
在隨著尺度降低至奈米等級時，黏附現象顯現出對接觸界面影響的重要性，因此在精密機械或微機械之微米至奈米波峰表面時必須考量此種效應，然而很多精密機械在接觸時，其接觸面積在受壓接觸時，會有磨擦現象產生，因此以其磨擦現象加以進行探討。分析結果顯示橢圓率增加、軟塗層與界面黏附力將引起真實接觸面積的增加，在黏附力越大，碎形粗度參數愈小與外力愈小時，其增加量亦增加，並且在黏附力固定時，模擬硬度曲線係數m值的減少，也將使真實接觸面積增加，另外真實接觸面積會隨著碎形維數由1.1的增加而增加，在碎形維數達到某ㄧ最大值時會達到極大值，然後隨著碎形維數的增加再減少，此臨界碎形維數受外力、碎形粗度參數、硬度對降伏應力之係數、材料特性等性質影響，其模式可供未來進行製造與設計之分析參考。

關鍵字

微磨潤 ； 表面形貌 ； 黏附磨損 ； 黏附磨擦 ； 碎形 ； 橢圓體 ； 彈塑性 ； 塗層硬度 ； 精密機械

並列摘要

Most machined surfaces are oriented with respect to the direction of the machine tools relative to workpieces. In such cases, the profile of the asperities generally contains various curvature for various directions. In accordance with these facts, anisotropic roughness must be considered. In order to minimize the adhesive and wear problems of precise machine, numerous coating methods are being designed to improve these surface properties. In this work, fractal characterization of surface topography is applied the new contact model of rough surface in considered incorporating ellipticity, hardness effects in coating film and adhesive properties to the study of contact mechanics. According to the experimental measurement of Silicon surface, fractal parameters were calculated to determine the contact characteristics of real surfaces.
Adhesion occurs at the peaks of the asperities and is pronounced when the surface roughness effect is small. In order to account for the effects of asperities ranging from the nanometer to micrometer level in micro-machine or precision machine. This results show that the real contact area increases with the increase in adhesion force and decrease in the hardness of coating film. At the same external load and D=1.5, the higher the effective radius ratio of surface roughness, the higher real contact ratio for soft film and the smaller real contact ratio for hard film. The contact area ratio increases due to the increase of the effective radius ratio, applied load and adhesion force and the decrease of hardness of coating film. High adhesion force and low hardness of coating film easily leads to a constant value of real contact area under low external loads region. It indicates that the surface force dominant the contact behavior between contacting surfaces under this condition. Regardless of the size of the hardness of coating film, the effective radius ratio give the negligible effect on real contact ratio for D=1.1. The friction coefficient increases with the decrease of hardness and increase of effective radius ratio.

並列關鍵字

microtribology ； surface topography ； adhesive wear ； adhesive friction ； fractal ； ellipsoid ； elastic-plastic ； coating hardness ； precision machine

參考文獻

[1] Pashley, M. D., Pethica, J. B. and Tabor, D., 1980, “Adhesion and Micromechanical Properties of Metal Surfaces,” Wear, Vol. 100, pp. 7-13.

[2] Chowdhury, S. K. and Gbosh, P., 1994, “Adhesion and Adhesional Friction at the Contact Between Solids,” Wear, Vol. 174, pp. 9-19.

[3] Greenwood, J. A., 1997, “Adhesion of Elastic Spheres,” Proc. Roy. Soc. London, A453, pp. 1277-1297.

[4] Johnson, K. L. and Greenwood, J. A., 1997, “An Adhesion Map for the Contact of Elastic Spheres,” Journal of Colloidal Interface Sci., Vol.l92, pp. 326-333.

[5] Sahoo, P. and Roy Chowdhury, S. K., 1996, “A Fractal Analysis of Adhesive at The Contact Between Rough Solids,” Proc. Instn. Mech. Engrs., Vol.210, pp. 269-279.