The frictional contact of coated bodies. Part I – The sliding contact (original) (raw)
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The frictional contact of coated bodies. Part II – The slip-stick contact
IOP Conference Series: Materials Science and Engineering, 2019
Fretting is a special wear mode that occurs in a contact subjected to minute relative motion by vibration or other perturbations. The solution of the slip-stick elastic contact is required to address the problem of tractions and stresses arising in a fretting contact. This solution may be particularly difficult to obtain for coated bodies, considering that, unlike the case of homogenous materials, the response of layered materials to unit load has not yet been expressed in closed form. However, explicit expressions, also known as the frequency response functions, have been derived in the Fourier transform domain. Considering that displacement and stress calculation in an elastic contact process yields convolution products arising from superposition of effects, the existing frequency response functions can be used to calculate the response of layered materials directly in the spectral domain, and subsequently transferred to the space domain. Once a method for elastic displacement cal...
Sliding frictional contact analysis of a monoclinic coating/isotropic substrate system
Mechanics of Materials, 2019
Owing to innovative developments and the need to satisfy the requirements of engineering applications, new and improved materials are investigated by engineers to compensate for the drawbacks of conventional materials. There is an urgent need for the tribology community to properly investigate the behavior of these materials before utilizing them in real life. In this study, the sliding frictional contact between a monoclinic coating/isotropic substrate system and a rigid cylindrical punch is provided using an analytical formulation and finite element method (FEM). The analytical expressions for the stress and displacement fields are presented, and the resulting singular integral equations (SIEs) are solved numerically. Details of the analytical formulation and the discretization used in the solution method for the SIEs are also presented. For obtaining the numerical solution, an augmented finite element method is used with plane strain conditions and 6-node higher order finite elements. According to the results, the analytical formulation and FEM results are consistent. Using different lamina orientations, coefficient of friction, and geometric/material parameters, provides the tribology community with a highly qualified parametric study that informs surface wear and surface fatigue crack initiation in contact mechanics problems
Tribological investigations of the load, temperature, and time dependence of wear in sliding contact
PloS one, 2017
An effort was made to study and characterize the evolution of transient tribological wear in the presence of sliding contact. Sliding contact is often characterized experimentally via the standard ASTM D4172 four-ball test, and these tests were conducted for varying times ranging from 10 seconds to 1 hour, as well as at varying temperatures and loads. A numerical model was developed to simulate the evolution of wear in the elastohydrodynamic regime. This model uses the results of a Monte Carlo study to develop novel empirical equations for wear rate as a function of asperity height and lubricant thickness; these equations closely represented the experimental data and successfully modeled the sliding contact.
Tribology International, 2007
A numerical contact model is used to study the influence of surface roughness and the pressure distribution on the frictional behaviour in rolling/sliding contacts. Double-crowned roller surfaces are measured and used as input for the contact analysis. The contact pressure distribution is calculated for dry static contacts and the results are compared with friction measurements in a lubricated rolling/sliding contact made with a rough friction test rig. The mean pressure is suggested as a parameter that can be used to predict the influence of surface roughness on the friction coefficient in such contacts. The results show two important properties of the friction coefficient for the friction regime studied in this paper: (1) there is a linear decrease in friction coefficient as a function of the slide-to-roll ratio, and (2) the friction coefficient increases linearly with increasing mean contact pressure up to a maximum limit above which the friction coefficient is constant. The absolute deviation of experimental results from the derived theory is for most cases within 0.005. r
Multi layered finite element analysis of graded coatings in frictional rolling contact
international journal of advanced design and manufacturing technology, 2015
A plain strain analysis of frictional rolling contact on an elastic graded coating is presented in this paper. Finite element method is applied to gain an understanding of the stresses and contact zone properties caused during rolling contact. The effects of friction, material stiffness ratio and coating thickness on stresses in contact zone and coating/substrate interface are studied. Shear modulus of softening and stiffening graded coatings change with exponential, power law and linear functions. The substrate is homogenous and the rigid cylindrical roller moves in a steady state condition with constant velocity. The coating is modeled in multi layers and a 2-D hard contact of rolling surfaces is considered. The analytical results verify the present method and show a good agreement. It is shown that thinner thicknesses have more effects on stresses and energy density, but these effects are not seen for thicknesses larger than a specific limit.
Tribological contact analysis of a rigid ball sliding on a hard coated surface
Surface and Coatings Technology, 2006
The stress and fracture conditions of a coated surface, that are the origin to wear, were analysed by three-dimensional finite element method (FEM) modelling on microlevel, by stress and strain computer simulations and by experimental studies with a scratch tester. The studied tribological contact was a 0.2 mm radius diamond ball sliding with increasing load on a thin, 2 Am thick titanium nitride (TiN) coating on a flat high speed steel substrate. The ball was modelled as rigid, the coating linearly elastic and the steel substrate elastic -plastic taking into account strain hardening effects. The stresses and strains generated in the surface during sliding are the result of four different mechanisms: the pulling and pushing by the friction force; the geometrical indent, groove, and torus shaped deformations of the flat surface; the bulk plasticity concentration and curvature minimum effects; and the residual stresses in the coating. In a sliding contact the first crack is initiated at the top of the coating from bending and pulling actions and it grows down through the coating. In the modelled scratch tester system a complex stress field is formed at the surface including remaining residual stresses in the coating behind the sliding contact. The stress fields are very different in a scratched uncoated steel sample. Some residual tensile stresses are formed in the groove behind the tip but they are very much lower than for the TiN coated case. A displacement controlled FEM model was found to better represent the real situation and correspond to experimental results than a force controlled model. D
Maximum von Mises Stress in the Sliding Contact of Coated Bodies
Tribology in industry, 2019
Competent design decisions for the optimum configuration of a coated contact require the prediction of the stress state developing in the coated body under contact load. Conventional methods of superposition of effects applied in the elasticity of homogenous bodies fail in case of multilayered materials as the response of the latters to point load has only been derived in the frequency domain. A technique for assessment of the elastic response of coated bodies to arbitrary loadings is advanced in this paper, by employing the convolution theorem in the calculation of the stresses and displacements resulting in a sliding contact process. The solution of the elastic frictional contact in full sliding is achieved iteratively, using a state-of-the-art method originally developed for the contact of rough homogenous bodies. Results presented in the literature for the sliding contact of coated bodied are replicated using the newly proposed algorithm. A parametric study is subsequently performed to assess the combined influence of the frictional coefficient, the coating thickness and the elastic modulus mismatch between the coating and the substrate, on the locations and intensity of the maximum von Mises equivalent stress.
Sādhanā, 2020
The application of coating gets exceptional importance since it improves the tribological properties of the contacting surfaces. Different input parameters like coating deposition processes, coating material properties and its thickness, use of lubricant and its additives, surface roughness and temperature affect the tribological properties and the rolling contact fatigue (RCF) life of coated rolling and sliding contact elements. In this paper, an attempt has been made to review for the clear understanding of the effect of these input parameters on the RCF life and tribological performance of coated rolling and sliding contact elements. It has been observed that coating deposition process must be chosen based on technical and economic aspects. Among the different techniques, thermal spraying technique is cost effective, and it also provides better bonding strength, which improves the RCF life in comparison with other techniques. Similarly, the effect of other input parameters has been reviewed and possible combination of the input parameters that help improve the performance of coated contacting elements summarized. Furthermore, the current status of research and the scope of future work to be carried out, in this area, have been outlined.
On the behavior of friction in lubricated point contact with provision for surface roughness
2010
This paper presents a simple approach to predict the behavior of friction coefficient in the sliding lubricated point contact. Based on the load-sharing concept, the total applied load is supported by the combination of hydrodynamic film and asperity contact. The asperity contact load is determined in terms of maximum Hertzian pressure in the point contact while the fluid hydrodynamic pressure is calculated through adapting the available numerical solutions of elastohydrodynamic lubrication (EHL) film thickness formula for smooth surfaces. The simulations presented cover the entire lubrication regime including full-film EHL, mixed-lubrication, and boundary-lubrication. The results of friction, when plotted as a function of the sum velocity, result in the familiar Stribeck-type curve. The simulations are verified by comparing the results with published experimental data. A parametric study is conducted to investigate the influence of operating condition on the behavior of friction coefficient. A series of simulations is performed under various operating conditions to explore the behavior of lift-off speed. An equation is proposed to predict the lift-off speed in sliding lubricated point contact, which takes into account the surface roughness.