Friction of polymeric materials

The case of contact of polymer and metallic surface has been examined. A formula is proposed for calculating the contact area as a function of time of holding the compression surface under load and for calculating the coefficient of friction, the dependence of Young's modulus and shear strength on temperature, deformation rate, and average force on the contact surface being taken into account. The nature of deformation of irregularities on the surfaces of polymeric materials under the action of normal and tangential loading has been examined.See [1] for Communication 1.Institute for Polymer Mechanics, Academy of Sciences of the Latvian SSSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 809–815, September–October, 1972.     

Friction of polymeric materials

The dry friction between a polymeric and a metallic surface is considered on the assumption that the friction power is such that heating of the surfaces can be neglected. The effect of the dimensionless specific load (ratio of nominal stress to elastic hardness of the polymer) on the friction process of elastomers and rigid polymers is analyzed and expressions are given for calculating the coefficients of friction of these materials at large values of the nominal stress.

     

Effect of sliding velocity on area of real contact and on force of friction in high-elastic materials

The velocity dependence of the force of friction and the area of real contact of SKN-18, SKN-26, and SKN-40 rubbers has been simultaneously determined on an optical instrument. In the region of small sliding velocities the area of real contact is virtually independent of the sliding velocity, while the force of friction increases in proportion to the logarithm of the sliding velocity, in accordance with the molecular-kinetic theory of friction. At high sliding velocities a deviation in the velocity dependences of both quantities is observed. The constant of friction has been determined over the entire velocity range and the resulting velocity dependence is examined in molecular terms.Mekhanika Polimerov, Vol. 3, No. 2, pp. 309–311, 1967     

Effect of normal load on the temperature and velocity dependence of the force of friction for high-elastic materials

The problem of the effect of normal load on the temperature and velocity dependence of the force of friction is examined for rubbers based on SKN-18, SKN-26, and SKN-40. In the temperature range from 18°–100°C the force of friction for these rubbers falls linearly with increase in temperature. The effect of loads up to 10⁷N/cm² on the temperature dependence of the force of friction for SKN-18, SKN-26, and SKN-40 rubbers reduces to a change in the real contact area or an increase in the temperature dependence with increase in load.The velocity dependence of the force of friction for SKN-18 rubber reveals a weak dependence of the activation energy and the average "jump distance" of the molecular chains on specific load. In the low-velocity region the force of friction depends linearly on the logarithm of velocity, at velocities above 0.44 cm/min and pressures of 30×10⁵ N/cm² the force of friction increases sharply due to an increase in uncontrolled heating of the friction surfaces.Mekhanika Polimerov, Vol. 1, No. 4, pp. 123–129, 1965     

Influence of temperature and humidity on the creep of polymeric materials. 4. Prediction on the basis of field test results

Conclusions Comparison was made of the results of prolonged (from 2 to 6 years) control experiments of tubular specimens of PN-3 for creep during tension, torsion, and simultaneous tension and torsion under various temperature-humidity conditions with calculation based on data of short-term (up to 5 h) experiments, in which the creep process was accelerated by increase in temperature and humidity of the material. Calculation of the prolonged creep deformations expected was done from the relationships of viscoelastic properties of a linearly changing solid, generalized for the case of influence of temperature and humidity under the assumption that the volume changes only elastically. On the basis of this generalization, adherence to the temperature-humidity-time analogy is assumed to be experimentally confirmed. Satisfactory agreement of results of prediction and prolonged control experiments is established.For communication 3 see [3].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 982–987, November–December, 1976.     

Temperature dependence of Young's modulus and the absorption coefficient of certain polymeric materials

The procedure and the results are described of the experimental determination of Young's modulus and the absorption coefficient as a function of temperature of polymeric materials, polystyrene foam, polyarylite, and others, obtained in dynamic investigations.     

Applicability of the hysteresis friction model for estimation of the degree of inelasticity of polymeric materials. I

Conclusions It has been established that the inclusion of the hysteresis friction model as an approximate method of taking into account the degree of inelasticity of polymeric materials is useful in many cases, and the investigations in this direction are promising in particular for the purpose of refining in this approximation those procedures of acoustical measurements which do not at present yet have a proper theoretical basis in the viscoelastic formulation of the problem.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 147–153, January–February, 1978.     

Effect of temperature and moisture on the creep of polymeric materials 1. One-dimensional extension under stationary temperature-moisture conditions

Creep tests have been carried out on PN-3 polyester resin for one-dimensional tension in the linear region of the stress-strain relation at various fixed values of the temperature and moisture content of the material. The temperature and moisture dependence of the instantaneous elasticity and creep characteristics of the material have been determined. It is shown that time-temperature-moisture superposition can apply in creep under various fixed temperature-moisture conditions.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 393–399, May–June, 1975.     

Deformation and sliding friction of polyurethane in the presence of a lubricant

The relation between coefficient of friction and elastic and high-elastic strains is investigated with reference to polyurethane subjected to friction in various liquid media. It is shown that a definite relationship between these parameters does exist. The effect of various liquids on the elastic and high-elastic deformation of polyurethane is studied.Kiev Institute of Civil Aviation Engineers. Translated from Mekhanika Polimerov, Vol. 5, No. 2. pp. 357–359, March–April, 1969.     

Effect of lubricating greases on rubber-metal sliding friction at high temperatures

The effect of sliding velocity and temperature on the lubricating action of greases has been investigated under constant and variable temperature conditions. The most important factor is the friction temperature. Two different temperature regions, separated by a change in the type of friction, have been detected. A method has been developed for evaluating the lubricating effect of greases.Scientific-Research Institute of the Rubber Industry, Moscow. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 876–880, September–October, 1968.     

Prediction of the deformation and fracture of polymeric materials

Research on the development of express methods of estimating the long-term deformation of polymeric materials based on the use of the time-temperature, time-stress, time-vibration, and time-moisture analogies (superposition) is briefly reviewed. Questions of the multiparameter prediction of the creep of plastics with parallel and serial application of the various analogies are considered. A program of further research is outlined. The possibility of predicting the fracture processes of polymeric composites and estimating the comparative strength of the products obtained from them on the basis of the acoustic emission and thermal radiation effects is demonstrated.Presented at the 2nd All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1971.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 498–514, May–June, 1972.     

Temperature dependence of the coefficient of friction of Ftorlon-graphite fiber

The reduced friction of Ftorlon (fluoroplastic) — graphite fiber against steel on the temperature interval 120–190°C is examined.Khmel'nitskii Technological Institute of Maintenance and Repairs. Translated from Mekhanika Polimerov, No. 6, pp. 1120–1121, November–December, 1973.     

Method of determining the coefficient of friction of polymer monofilaments

An instrument for determining the coefficient of friction of technical polymer monofilaments (100 µ or more in diameter) under various conditions is described and the experimental procedure is explained.Gubkin Moscow Institute of the Petrochemical and Gas Industry. Translated from Mekhanika Polimerov, No. 4, pp. 729–731, July–August, 1971.     

Approximation and numerical realization of 3D contact problems with given friction and a coefficient of friction depending on the solution

The paper presents the analysis, approximation and numerical realization of 3D contact problems for an elastic body unilaterally supported by a rigid half space taking into account friction on the common surface. Friction obeys the simplest Tresca model (a slip bound is given a priori) but with a coefficient of friction $ \mathcal{F} $ \mathcal{F} which depends on a solution. It is shown that a solution exists for a large class of $ \mathcal{F} $ \mathcal{F} and is unique provided that $ \mathcal{F} $ \mathcal{F} is Lipschitz continuous with a sufficiently small modulus of the Lipschitz continuity. The problem is discretized by finite elements, and convergence of discrete solutions is established. Finally, methods for numerical realization are described and several model examples illustrate the efficiency of the proposed approach.