The main goal of this study is to present a model to investigate the effect of nano-particles’ weight fraction on the friction coefficient of rough contact in the mixed-lubrication regime. Experimental testing involves pin-on-disk measurements of the friction coefficient with CuO nano-particles added to engine oil. Theoretical analyses involve developing a method for treating an EHL line contact with provision for surface roughness that takes into account the load-carrying capacity of surface asperities, lubricant, and nano-particles. Results show that theoretical and experimental results for friction coefficients are in good agreement. A parametric study is conducted to investigate effect of load, the geometry of the nano-particles, and their mechanical properties as well as their weight fraction on the friction coefficient.
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