| It has become an emerging trend in tribology design to lubricate the lubrication points with limited lubricant supply(LLS),so that the machine parts can work in the optimal lubrication regime for reducing wear and friction,and decreasing power consumption from oil stir and friction.Under limited lubricant supply,the lubricant distribution on the lubricated surfaces can be controlled by surface modification,so as to achieve desired lubrication efficiency.At present,the methods used include plating,chemical coating,surface texture and so on.Oiliness additive can form adsorption film on the friction surface,and then its surface energy can be changed.In the meaning time thus the limited lubricant supply can be changed,but there is no research in this area.In this thesis,the slider-on-disc conformal contact oil film lubricating measurement system was used to modify the surface energy of the lubricated surface through in-situ adsorption of stearic acid oil agent.The corresponding oil film thickness was studied under limited lubricant supply,and the adsorption of stearic acid was characterized.The main contents include:(1)Under conditions of different disc surface modification,the influence of stearic acid adsorption on the establishment of LLS oil film was studied.The ultraviolet illumination and plasma cleaning were used to modify disc surface.The influence of stearic acid added to PAG base oil on the lubrucation film thickness was measured with the original disc and the modified disc surface.On the surface of the original disc,the film thickness of PAG with stearic acid was lower than that of pure PAG.Both UV and plasma treatment promoted the adsorption of stearic acid on the disc surface.Compared with the original disc,the film thickness with the UV treated disc decreased,while the oil film thickness with the plasma treated disc increased under certain conditions.(2)With different base oils,the influence of stearic acid adsorption on the establishment of oil film with limited lubricant supply was studied.The thickness of three base oils,PAO10,silicone oil and PAG,and those with stearic acid was measured.The results show that base oils show different distribution on the lubrication track,and oil supply presents different forms at the inlet of the contact,which affects the film thickness.In lubrication,stable stearic acid adsorption needs the continuous supply of lubricant containing stearic acid in order to achieve the balance between the repair and damage of the adsorption film.The influence of base oil on the adsorption of stearic acid was characterized by contact angle measuring,interferometric image acquisition on lubrication track,oil pool observation by fluorescence method and atomic force microscope.(3)Considering that stearic acid can form adsorption film on the disc surface and the slider surface which can low their surface energy,four synergy mechansims including local inlet load-bearing effect,interface slip effect,oil replenishment effect and surface tension gradient effect are proposed under limited lubricant supply.Based on these 4mechanisms,the experimental phenomna in(1)(2)are explained.(4)The influence of two different types of inlet oil supply on the film thickness and film pressure were numerically calculated.Based on the experimental observations,two oil supply models,i.e.,two-side-ridge model and discrete strip model,were established,and the lubrication behaviour of the slider-on-disc contact in the experiments was numerically calculated by using the modified Reynolds equation with fractional film content.The results show that under certain conditions,the discrete oil supply by surface dewetting is better than the thin oil layer with two-side-ridges,and the film thickness is higher,which is qualitatively consistent with the experimental results.The numerical results also verify the inlet local load-bearing effecte,that is,the discrete lubricating oil supply generated by dewetting can produce the hydrodynamic effect ealier when the oil entering the contact. |
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