In this paper,we first discuss the development of the field of tribology,and highlight some of the main problems encountered in this area,such as lack of systematicness,loose correlation,and inadequate focus on the microscopic perspective.Then,we provide basic formulas of frictional mechanics while considering the friction effect on classical mechanics formulae.In order to carry out the frictional mechanics analysis,we first classify the interface.According to the size analysis of surface films,the manufacturing roughness of the surface,the contact width,and the roller radius of the rolling contact bearing,frictional mechanics has the features of interface mechanics,while interfaces are classified based on the presence or absence of a medium.Based on the classification,we further analyze the pressure and frictional stress of sliding and rolling friction problems without a medium,such as a slider,wedge key,and V belt.We also analyze problems with a medium,such as journal and rolling contact bearings.By comparing these results with those of classical mechanics without considering friction,we see that(1)friction causes deviations in the result for classical mechanics which does not consider friction,and(2)if the frictional stress and normal pressure affect each other,their interaction should be considered simultaneously.Finally,we summarize the friction problems,namely,sliding and rolling,with and without a medium,and deformed and non-deformed.From our analysis,we propose two conclusions.First,the frictional mechanics problem is a deviation of the classical mechanics problem,and secondly,frictional stress and normal pressure influence each other.
The adhesion between two parallel solid surfaces is of great interest with the rapid development of micro-nano devices and instruments.The adhesion forces between a flat tip with a diameter^1.7μm and some surface have been determined by recording the force-displacement curves with an atomic force microscope(AFM).The flat tip is used to prevent wear and mimic the adhesion between two parallel surfaces.The free energy of the solid surface is calculated by the contact angles between the probe liquids and the surface.The adhesion force between parallel solid surfaces cannot be predicted by the theory of thermodynamic surface free energy.The adhesion measurements were carried out under ambient conditions,in a nitrogen-filled glove box,under distilled water,and under potassium chloride(KCl)solution.The outcome shows that the real contact area without the applied load is only a small proportion of the apparent contact area.The measurement stability and repeatability of adhesion by the AFM depend on the surface characterization,measurement methods and the environment.Under different environments,there are different interactions and factors affecting the adhesion force,and the dominant interactions and factors may be different too.The various interactions and factors are mutually coupled to determine the final adhesion force.
