The Basic Research On Deformation Behavior Of Surface Texture In Soft-EHL Contacts

Surface texturing is an efficient method to enhance the lubricating properties of friction pairs.Large elastic deformation is prone to occur in textured soft contacts under hydrodynamic lubrication,which aggravates the complexity of tribological properties and brings some difficulties to conduct corresponding research.In this paper,the deformation process of the textured surface is studied,the deformation law and mechanism are systematically analyzed.Firstly,a two-dimensional elastohydrodynamic numerical simulation is conducted for surface textured sliding bearings.The effect of surface elastic deformation on lubricating properties is investigated.The influence of texture parameters on the load carrying capacity,pressure and deformation distribution are discussed.The results showed that elastic deformation can directly increase the local film thickness,lead to a clearance divergence in the sliding direction and finally deteriorates the hydrodynamic effect of the texturing on the load carrying capacity.Among the design parameters of the surface texture,the priority should be given to the texture area ratio,followed by the texture depth diameter ratio in order to obtain the maximum load carrying capacity of the texture surface.The optimal texture area ratio is closely related to the working condition.As for the ratio of texture depth to diameter,the larger the value,the stronger the load carrying capacity.Then,in-situ observation of the deformation behavior of surface texture under hydrodynamic lubrication condition is realized and conducted by using optical interferometry.The deformation law and mechanism are systematically analyzed,in addition,the geometrical shape and distribution effect of surface texture on the deformation are investigated respectively,finally,the deformation of bionic hexagonal pillar-textured surface during drainage process are studied in detailed.The observed results from singly dimpled surface under hydrodynamic condition showed that,in addition to the hydrodynamic pressure,viscous shear force is another important reason for the deformation of the textured surface.The deformation pattern and corresponding mechanism are closely related to applied load and wedge configuration.Convergent wedge area of the texture presents a concave deformation under the dominant effect of hydrodynamic pressure.While the deformation of the divergent wedge area is closely related to the effect of viscous shear force.The observed results for dimpled surface with different geometrical shapes showed that the deformation degree,including the maximum and deformed scope,closely depends on the geometrical shape of dimple.And the geometrical shape effect becomes increasingly remarkable as the growth of applied load.The minimum elastic deformation emerges around the elliptical dimple with major axis perpendicular to sliding direction,while the textural shape with sharp-angled converging edge,such as triangular and diamond dimple,induces more severer elastic deformation.The observed results for dimpled surface with different spatial arrangements showed that the action range of a single dimple would be compressed by surrounding dimples.The effect of spatial arrangement on the elastic deformation is mainly laid on the change of pressure distribution across the dimple,which becomes increasingly remarkable as the growth of applied load.Both the value and area for pressure build up across a single dimple in square arrangement presents to be smaller,which results in a more alleviated and limited elastic deformation.The hydrodynamic pressure plays a dominant role in the deformation of bionic hexagonal pillar-textured surface under full film lubrication,the contact surface mainly presents concave deformation.With the increase of load,the concave deformation shows a tendency of dispersion.In the process of drainage,the depression deformation of the hexagon pillar can store the residual liquid film under the pressure of the squeezed oil film.Based on the minimal residual liquid film,an optimized geometry for hexagon pillar is proposed.The results of this paper can provide a reference of surface deformation for the design and application of surface texture on soft materials.