I. G. Goryacheva

Wear in Partial Slip Contact

An analytical method that evaluates the evolution of stress and surface profile in fretting under the partial slip conditions is presented. The repeated slip occurring near the edges of contact generates wear that changes the contact geometry and contact stresses. The method is based on two scales of time: time for one cycle of the oscillating tangential force and time corresponding to the number of cycles. Archards wear law is used to evaluate wear and gap variation within the slip zones during one cycle. The governing integral equations are reduced to calculate the contact pressure after each cycle. Evolution of the contact characteristics (contact pressure and shear stress, contact width, gap and slip functions) in fretting is calculated using a stepwise procedure. It is shown that the size of stick zone does not change in wear process of bodies with similar elastic properties under the constant amplitude load conditions, and that an asymptotic solution corresponding to the number of cycles approaching to infinity exists. Analytical expressions for the asymptotic contact pressure, shear and tensile stress, and the gap function are presented. It is proved that the asymptotic contact pressure and shear stress are singular at the ends of stick zone. Detailed results are given for two initial shapes of elastic indenter contacting with an elastic half-space: for the parabolic cylinder and for the indenter having a flat base with rounded edges.

Contact characteristics of a rolling/sliding cylinder and a viscoelastic layer bonded to an elastic substrate

Abstract The rolling or sliding contact of an elastic cylinder and a layered foundation has been investigated. The substrate of the foundation was modeled as a two-dimensional elastic half-space. The one-dimensional Maxwell model was used to describe the normal and tangential compliance of the viscoelastic surface layer bonded to the substrate. Conditions of partial and full slip within the contact area were considered. The Fredholm integral equation of the second kind was obtained to define the pressure distribution within the contact area. It has been established that the contact characteristics (i.e. pressure distribution, size and displacement of the contact zone and the indentation of the cylinder into the viscoelastic layer) depend on three non-dimensional parameters. Using these parameters the dependence of the contact characteristics upon the load, velocity, geometrical and mechanical properties of the contacting bodies was investigated. A model has also been developed to describe the traction at the contact interface of the elastic cylinder and the layered foundation. The model was used to analyze and determine the distribution and size of the slip and no-slip zones for different values of viscoelastic layer properties and sliding friction coefficients. As a result of the stress analysis, the rolling friction coefficient has been determined and investigated as a function of the non-dimensional parameters under consideration.

The effect of interface imperfection and external loading on the axisymmetric contact with a coated solid

A method is proposed to solve a contact problem for an elastic punch and elastic layer bonded to an elastic half-space. The boundary conditions at the interface model the imperfect adhesion between the layer and substrate. The effect of additional loading applied to the layer outside the contact region is taken into account. The solution of the axisymmetric contact problem is obtained by using Hankel transform and iteration methods. The stresses within the coated body which is in contact with the spherical punch or with the punch having a flat base and rounded edges are calculated. The analysis of the dependence of the contact characteristics and stresses inside the coated body on the geometrical and mechanical properties of the layer and the substrate, parameter characterising the imperfect adhesion, punch shape, and an additional load is presented.

Adhesive interaction of elastic bodies

Abstract The unified formulation of the axisymmetric problem of adhesion between elastic bodies and a method of solving it are presented. The adhesion is caused by either the surface energy of the bodies or menisci of fluid present in the contact zone. Both contact of the bodies and the case of the separated bodies are analysed. The values of the parameters for which the dependence of the load on the change of distance between the bodies becomes non-unique are determined. The loss of energy in an approach/separation cycle between the bodies as a function of the basic parameters of the problem is investigated analytically and numerically.

Internal Stresses in Contact of a Rough Body and a Viscoelastic Layered Semi-Infinite Plane

A model has been developed to investigate the effects of a rough elastic indenter in sliding contact with a viscoelastic layer bonded to an elastic semi-infinite plane. The viscoelastic layer is modeled as a one-dimensional Maxwell solid (small strain) while the substrate of the semi-infinite plane is modeled as a two-dimensional elastic half plane. The Fredholm integral equation of the second kind was obtained to determine the contact stresses. The results indicate that the viscoelastic properties of the layer and the velocity of the indenter significantly affect the contact pressure and internal stress distributions. The viscoelastic layer causes the pressure and internal stresses to become nonsymmetrical. High asperity densities reduce the amplitude of maximum shear stress at a fixed depth below the surface. Results are also presented for various coefficients of friction.

Modeling of friction at different scale levels

We construct a model for studying the common influence of the imperfect elasticity of actual bodies, the microgeometry of their surfaces, and their adhesive interaction on the contact characteristics (the contact pressure distribution, the region of actual contact) and on the sliding friction force. The model is based on the solution of a plane contact problem of sliding of a rigid body with a regular relief on the boundary of a viscoelastic foundation with surface molecular attraction in the gap between the surfaces taken into account. We analyze the influence of the surface microgeometry parameters at different scale levels on the character of the surface interaction (the saturated or discrete contact) and the friction force for different sliding velocities of the contacting bodies.

Effect of aluminum-alloy composition on self-lubrication of frictional surfaces

The influence of the mechanical and geometric characteristics of the hard and soft phases of an anti-friction alloy (yield limits of these phases, size and concentration of inclusions) on the amount of the solid lubricant appearing on the frictional surface is analyzed. The results obtained are used both to describe the existing anti-friction aluminum alloys and to give the recommendations for creating new wear- and score-resistant alloys.

Contact problem with partial slip for the inclined punch with rounded edges

Abstract The 2-D contact problem for the inclined punch having a flat base and rounded edges and an elastic half-space is considered. It is assumed that the applied forces provide for conditions of partial slip within the contact region and that the contacting bodies have similar elastic properties. The analytical expressions for distribution of contact pressure and shear stresses, the σx stress component, slip displacement, etc. are reduced based on Muskhelishvili’s method. It is shown that only one stick zone exists within the contact region. The location of the contact region and the stick and slip zones are analyzed for various external conditions. The model is used to evaluate the dependence of the stresses within and near the contact zone, on the normal and tangential forces and the moment applied to the indenter and the particular indenter geometry.

Viscoelastic effects in lubricated contacts

Abstract The effect of viscoelastic layer on pressure, film thickness and friction coefficient in lubricated contacts has been investigated. The model consists of two elastic rollers coated with viscoelastic layers and separated by a thin film of lubricant. The results indicate that under low velocity conditions the friction coefficient monotomically reduces to a minimum and then increases as the speed increases. The results also indicate that for low velocities the contact characteristics are dominated by the properties of the viscoelastic layer and the elastic substrate and as the speed increases, the viscoelastic layer effect becomes negligible.

Multiple contact model in the problems of tribomechanics

Abstract A new parameter is introduced into the contact model of rough surfaces which characterizes the contact spot density. Based on the present mathematical model, a number of the specific characteristics of discrete contact (the rigidity of the joint of rough bodies, the real area of contact) are studied and, also, the wear to roufhness (microasperites of real surfaces) is considered. the results are compared with know experimental regularities which are interpreted on the basis of this model.