On the wear of brake pads

Within measurements of brake pads on the IDS high load Tribometer, the wear of pads was investigated by a new non-contact wear measurement under low normal pressures and low temperatures. The first results show that the wear of the pad in the sliding friction is nearly proportional to the friction work, and inversely proportional to the shear strength. The results are also interpreted by the adhesion theory of friction and Archard's equation. On the basis of further interpretations of shear strength and extension of adhesion theory of friction, the wear is derived as a piecewise linear function, which can evaluate explicitly the effect factors of wear and relative correlations at different pressures and different temperatures. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The calculation of the energy losses in a sliding elastic contact with friction and wear (the plane problem)

The plane problem of the sliding contact of a punch with an elastic foundation when there is friction and wear is considered. Assuming the existence of a steady solution in a moving system of coordinates, relations are derived between the sliding velocity, the wear, the contact stresses and the displacements for an arbitrary dependence of the wear rate on the contact pressure. Taking into account the presence of a deformation component of the friction force, an equation is written for the balance of the mechanical energy for the punch - elastic base system considered. It is shown that the equality of the work of the external force in displacing the punch to the losses due to friction and the change in the shape of the foundation due to wear is satisfied when the work done by the contact stresses on the increments of the boundary displacements is equal to zero, and the frictional losses must be determined taking into account the non-uniformity of the distributions of the shear contact stresses and the sliding velocity in the contact area. Two special cases of the foundation in the form of a wide and narrow strip are considered, for which the total coefficient of friction is calculated, taking into account the deformation component of the friction force.     

Effect of orientation and crystallinty on the friction and wear of polytetrafluoroethylene

A study has been made of the laws governing the changes in wear of polytetrafluoroethylene (PTFE) in relation to the degree of crystallinity and the changes in friction and wear of preoriented PTFE in relation to the working conditions of the metal-polymer friction pair. From the experimental results, conclusions may be drawn concerning the possibility of increasing the wear resistance of polymers by modifying their structural characteristics.Mekhanika Polimerov, Vol. 2, No. 1, pp. 87–92, 1966     

Optimization of the composition and tribological properties of high-density polyethylene-calcite-silicon nitride composites by the method of experiment planning

The tribological characteristics (wear resistance, coefficient of friction ) of a high-density-polyethylene-base composite filled with calcite and highly disperse silicon nitride produced by the plasmochemical method are investigated experimentally. The experiment plan was compiled in the form of a simplex lattice, and new points were planned in conducting the experiments. Compositions possessing appreciably elevated wear resistance (by a factor of 500) and a coefficient of friction reduced by 20% as compared with the unfilled polymer were obtained. Institute of Inorganic Chemistry of the Latvian Academy of Sciences, Salasplis, LV-2169. Institute of Polymer Mechanics of the Latvian Academy of Sciences, Riga, LV-1006. Riga Mechanical University, Riga, LV-1050, Latvia. Translated from Mekhanika Kompozinykh Materialov, No. 5, pp. 690–695, September–October, 1996.     

Effect of loading rate on polymer wear

The effect of loading rate on polymer wear in metal-polymer friction pairs is considered. Investigations show that at low loading rates the wear resistance of the polymer specimens increases, evidently owing to orientation of the elements of the molecular structure in the surface layer. This finding applies both to dry friction and friction with lubricants.Mekhanika Polimerov, Vol. 2, No. 6, pp. 862–866, 1966     

Wear and fluid-solid-thermal transient coupled model for journal bearings

In this study, the transient interactions between the sliding wear behaviour and fluid–solid–thermal (FST) characteristics of journal bearings are revealed using an established mathematical model. The calculated temperature distribution is validated by a comparison with experimental results from the literature. Furthermore, a wear test for lubricated journal bearings is conducted to verify the predicted wear rate. The time-varying wear and FST performances of the journal bearing, including the wear rate, wear depth, fluid pressure, contact pressure, and maximum temperature are calculated numerically. Through numerical simulations, the effects of the boundary friction coefficient and surface roughness on the wear and FST performances are evaluated. To demonstrate the importance of considering the three-dimensional (3D) thermal effect during the wear analysis of lubricated journal bearings, the numerical results predicted by the isothermal model and the thermal model are compared systematically within a wide range of operating conditions. The numerical results reveal that the worn surface profile slightly decreases the maximum temperature. Additionally, the worn region is primarily located at both edges of the bearing, and the time-varying worn surface profile may be beneficial for improving the hydrodynamic effect. Furthermore, the effect of the 3D thermal characteristics on the wear prediction of journal bearings cannot be ignored when the external load, boundary friction coefficient, surface roughness are relatively large.     

Efficiency of capron single fibers in a friction unit. I

Changes taking place in the degree of orientation and the surface state of capron single fibers in the course of stretching and wear are studied by x-ray structural and microscope analyses. The structure changes in different ways for single fibers of different stretch multiplicities (stretch factors) on subjection to wear tests. The optimum limit to the orientation of capron single fibers working under conditions of friction and wear is determined.     

Rolling Contact Problem with the Generalized Coulomb Friction

This paper deals with the numerical solution of the wheel - rail rolling contact problems. The unilateral dynamic contact problem between a rigid wheel and a viscoelastic rail lying on a rigid foundation is considered. The contact with the generalized Coulomb friction law occurs at a portion of the boundary of the contacting bodies. The Coulomb friction model where the friction coefficient is assumed to be Lipschitz continuous function of the sliding velocity is assumed. Moreover Archard's law of wear in the contact zone is assumed. This contact problem is governed by the evolutionary variational inequality of the second order. Finite difference and finite element methods are used to discretize this dynamic contact problem. Numerical examples are provided. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Wear resistance of filled epoxypolyamide composites in aggressive media

The authors investigate the influence of certain aggressive media (toxic chemicals) on the wear resistance of filled epoxypolyamide composites. The presence of toxic chemicals in the zone of friction causes a sharp fall in the wear of the polymers. The maximum wear resistance is displayed by epoxypolyamide composites filled with iron powder, cement, or graphite.     

Friction and wear of polymer-based composites

Polymeric materials containing different fillers and/or reinforcements are frequently used for applications in which friction and wear are critical issues. This overview describes how to design high temperature-resistant thermoplastics, e.g., filled with carbon fibers and internal lubricants, for operation under low friction and wear at elevated temperatures as sliding elements in, e.g., textile drying machines. Further information will be given on the systematic development of continuous fiber/polymer composites with high wear resistance, and on attempts for the prediction of their load-bearing capacity using a finite element approach. Finally, the application of such composites in thermoplastic filament-wound journal-bearings is discussed.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Institute of Composite Materials (IVW), University of Kaiserslautern, D-67663 Kaiserslautern, Germany. Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 6, pp. 717–732, November–December, 1998.     

Effect of the surface activity of polymers during degradation on the friction and wear of plastic-metal and metal-metal pairs

The results of studies on the reasons why degradation products of polymers migrate into the metal and the metal is transferred into the plastic material during friction are discussed. Saturation of the steel surfaces with the degradation products of the polymers has been shown in the case of electropositive plastic counterbody, and decarbonization of steel surfaces in the case of the electronegative polymeric counterbody; a hypothesis has been put forward on the triboelectric and mechanochemical phenomena for the friction and wear processes of the plastic-metal and metal-metal pairs.Rostov-on-Don Institute of Railway Transport Engineers. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 520–525, May–June, 1973.     

Study of the thermophysical and antifriction properties of polyethylene-based compositions

The mechanical and antifriction properties of polyethylene filled with various, relatively hard fillers are determined. Filling with oxides and silicates produces the greatest increase in wear resistance. The coefficient of friction decreases with increase in the stiffness of the compositions.Mekhanika Polimerov, Vol. 3, No. 6, pp. 1070–1077, 1967     

Antifrictional properties of compositions in the polyamide - copper system

Conclusion 1. The antifrictional properties of metallopolymer compositions made up by a thermal method in an air atmosphere (method A) and in a hydrogen atmosphere (method B), and also made up by mechanical mixing of P610 polyamide powders and PM grade copper (method C) have been investigated.2. It has been shown that the metallopolymer obtained by the thermal method in a hydrogen medium, at a degree of filling of 30% or more by wt., has less wear of the composition as compared with compositions made up by method C which are similar in degree of filling.3. Compositions made up by method A have a loosened structure and are comparable in wear resistance with the unfilled polymer.4. The coefficient of friction of the metallopolymer obtained in a hydrogen medium is less at the selected slippage regime than the coefficient of friction of the pure polyamide by a factor of 1.5, and is 20% less than that of the metal-filled composition made up by mechanical mixing in accordance with method C.5. It has been shown that the temperature on the friction surface of the metallopolymer made up by method B is less than that of the pure polyamide or the metal-filled composition made up by method C, by 40°C and by 20°C, respectively.Lenin Young Communist League. Riga Institute of Civil Aviation Engineers. Translated from Mekhanika Polimerov, No. 6, pp. 1043–1048, November–December, 1978.     

Investigation of the Contact Interaction between Two Layers with Regard for the Temperature Dependence of Friction and Wear Coefficients

We consider the one-dimensional frictional contact problem of thermoelasticity for two layers. One of the layers has a mass and slides along the surface of the other one. We assume that the friction and wear coefficients depend on temperature, propose an iterative scheme of solution, and investigate contact characteristics.     

On wheel–rail contact problem with material properties varying with depth

Numerous laboratory experiments indicate that the use of a layer or a coating material attached to the conventional steel body reduce the magnitude of contact stress. Therefore in this paper we solve numerically the wheel–rail contact problem with friction and wear assuming the existence of a small elastic layer on the rail surface. Material properties of this layer are changing with its depth. The friction between the bodies is governed by Coulomb law. In contact zone Archard's law of wear is assumed. We take special features of this rolling contact problem and use so-called quasistatic approach to solve this contact problem. Finite element method is used as a discretization method. The numerical results including the distribution of normal stress along the contact boundary are provided and discussed. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Wear resistance of cured epoxy-novolac compositions

It has been established that changing the elasticity of rigid crosslinked epoxy-novolac block copolymers changes the friction mechanism and wear characteristics. The optimal conditions for obtaining block copolymers with the greatest wear resistance have been determined. The results of testing epoxy novolacs in neutral and alkaline media are presented.Leningrad Lensovet Technological Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1107–1109, November–December, 1969.     

Wear resistance of metal polymer combinations

The possibilities of using polymer protectors in journal bearings are investigated, and the effects of operating conditions on the wear of metal/metal-polymer composition friction pairs are investigated.Mekhanika Polimerov, Vol. 2, No. 4, 580–584, 1966     

Thermoelastic rolling contact problem with temperature dependent friction

The paper is concerned with the numerical solution of a thermoelastic rolling contact problem with wear. The friction between the bodies is governed by Coulomb law. A frictional heat generation and heat transfer across the contact surface as well as Archard's law of wear in contact zone are assumed. The friction coefficient is assumed to depend on temperature. In the paper quasistatic approach to solve this contact problem is employed. This approach is based on the assumption that for the observer moving with the rolling body the displacement of the supporting foundation is independent on time. The original thermoelastic contact problem described by the hyperbolic inequality governing the displacement and the parabolic equation governing the heat flow is transformed into elliptic inequality and elliptic equation, respectively. In order to solve numerically this system we decouple it into mechanical and thermal parts. Finite element method is used as a discretization method. Numerical examples showing the influence of the temperature dependent friction coefficient on the temperature distribution and the length of the contact zone are provided. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Wear resistance of steel and brass in friction against filled polyethylene

The wear resistance of a shaft in friction against polyethylene filled with abrasive filler particles (fiberglass, SiO₂) has been investigated. Compositions containing fiberglass can be successfully employed in combination with steel, but are not recommended in combination with brass. Compositions containing SiO₂ cause considerable wear of the steel shaft.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 940–942, September–October, 1969.