Abstract
Sliding between asperities occurs inevitably in the friction pair, which affects the efficiency and reliability in both lubricated and non-lubricated conditions. In this work, the contact parameters in the coated asperity sliding process are studied, and the universal expressions of the average contact force and the friction coefficient are obtained. The effect of the interference between asperities, the material and geometrical parameters including the Young’s modulus ratio and yield strength ratio of the coating and substrate, and the hardening exponent and thickness of the coating on the average contact forces and friction coefficient is considered. It shows both normal and tangential contact forces increase with the increasing interference, increasing Young’s modulus ratio, decreasing yield strength ratio, and decreasing coating thickness; while the trend is different for the effect of the hardening exponent of the coating. The normal force increases and the tangential force decreases as the hardening exponent increases. Based on this, the influence of these parameters on the effective friction coefficient is obtained further. It reveals that the friction coefficient increases as the interference and Young’s modulus ratio enlarge and decreases as the yield strength ratio, the coating’s hardening exponent, and thickness increase. The universal expressions for the contact force and friction coefficient in the sliding process are obtained. This work might give some useful results to help choose the optimum coatings for specific substrates to reduce friction in cases where the asperity contact exists, especially in the focused field of the journal bearing in the marine engine under poor lubrication conditions.
Highlights
In applications where relative movement exists, sliding between surfaces affects mechanical performance [1] or might cause fault in components and parts of different machines [2,3]
The sliding between a coated asperity and a homogenous asperity is studied, which exists in some applications, and the effect of the material and geometrical parameters of the coated asperity on the contact force and friction coefficient is explored
The sliding process between a coated asperity and a homogeneous asperity was studied to consider the frictional behavior of the crankshaft-bearing system in the marine engine on the micro scale
Summary
In applications where relative movement exists, sliding between surfaces affects mechanical performance [1] or might cause fault in components and parts of different machines [2,3]. For only a few works have considered the sliding process between coated asperities and given the general expression of the contact force and effective dynamic friction coefficient related to the geometrical and material parameters (especially for coated asperities with power-law hardening elastic-plastic coatings). The sliding between a coated asperity and a homogenous asperity is studied, which exists in some applications (e.g., the shaft and the bearing bush in the marine engine under very bad lubrication conditions, as mentioned before), and the effect of the material and geometrical parameters of the coated asperity on the contact force and friction coefficient is explored. In this work, the frictionless contact condition is adopted, and adhesion and failure are ignored to focus on this relation between the frictional behavior (e.g., contact force and friction coefficient) and the plastic deformation
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