Experimental Study On Point Contact EHL Problem With Variable Velocity Using Optical Interferencetric Technique

In this thesis,the oil film properties of elliptical contact and point contact under non-steady state conditions are studied.The work is divided into three parts: the effect of elliptical contact emergency stop on surface dimple under pure sliding condition,the experimental study of oil film characteristics under elliptical contact pure sliding reciprocating condition,and the varication of lubricating oil film under zero entraining velocity(ZEV)reciprocating condition.First of all,this thesis is aimed to experimentally explore the effect of a sudden stop on the variation of surface dimple phenomenon of elastohydrodynamic lubrication(EHL)in elliptical contact under simple sliding motion.By changing the entraining velocity and load,the transition of a “temperature-viscosity wedge” dimple into a squeezed entrappment of oil film by a sudden stop is investigated.As the load increases,the central film thickness increases at the initial stage and then drops sharply;the occurrence of the "temperature-viscosity wedge" dimple is earlier and the time when the dimple reaches the center of the contact zone becomes shorter.Second,the oil film variation under the process of simple sliding reciprocating in elliptical contact between a steel roller and a glass disk is studied.The transformation of the lubrication state from EHL to boundary lubrication(BL)and the occurrence of contact surface wear are studied.The stroke length is controlled by changing the motion period,and ? = a / L is defined to illustrate the relationship between the stroke length and the Hertz contact radius.The BL area in the contact zone gradually increases with the increase of the radius-stroke ratio.Finally,based on the "temperature-viscosity wedge",the film formation of EHL point contacts under ZEV condition is investigated.Experiments were conducted on a ball-on-disk test rig to explore the variation in oil film thickness under ZEV reciprocating motion.The oil film thickness between a ball surface and a sapphire disk was measured using the optical interferometry.The steel ball and the sapphire disk move at equal speeds but in opposite directions by a triangle wave.Under fully supplied oil lubrication conditions,three loads and three strokes were used to observe the shape of the oil film.The variations in the surface dimple phenomenon with applied load,maximum surface velocity and period were studied.The experimental results show that a horseshoe-shaped oil film appears in the initial stage of the reciprocating ZEV motion,and a wedge-shaped oil film is produced on the right side of the contact zone.