Heavily loaded line EHL contacts with thin adsorbed soft layers

Abstract

Studies of thin soft polymeric or metal layers adsorbed on the surfaces of lubricated solids showed lower friction coefficients and energy losses. The degree to which this reduction happens depends on the coating material nature, its rheology, and coating thicknesses, as well as other factors. To an extent, the application of such soft coatings is in its infancy and it is still not clear which parameters affect the performance of lubricated joints, and how. This paper attempts to model such coated lubricated contacts and to understand how soft coatings affect the joint performance. The paper presents a model of heavily loaded elastohydrodynamically lubricated (EHL) contacts of solids made of elastic homogeneous materials, the surfaces of which are covered by thin coating layers made of soft elastic material. The model incorporates not only normal but also tangential contact stresses and displacements. First, the effect of tangential contact stresses and displacements on the problem parameters is determined, and then the EHL problem is formulated and analyzed. It is necessary to account for variations in the solid surface linear velocities caused by tangential contact stresses. The deformation and displacement processes in thin coating layers are asymptotically modeled by certain boundary conditions. This is done using the Fourier transform with respect to the coordinate along the contact and making the necessary simplifications of the equations. The formulated EHL problem incorporates the normal and tangential contact surface displacements caused by normal and tangential contact stresses. The difference between the classic EHL problems and the problem at hand is due to variations in the linear surface velocities compared with the nominal ones. This causes significant changes in the contact friction parameters. The solution of the EHL problem is obtained numerically. A parametric analysis of the EHL problem solution is performed.