Consideration of friction between layers in determining the stress-strain state of structures with nonideal layer contact

A mathematical model for calculation of structures in a three-dimensional installation allowing for layer slippage with friction was constructed. The examples examined show that consideration of friction in problems of calculating laminated structures with nonideal layer contact can introduce an essential correction in the stress—strain state of the structure. In slabs with a freely sagging lower surface, friction is perceived for important friction coefficients and increases when the slippage surface approaches the loaded surface. In masses with a rigidly attached lower surface, even insignificant friction coefficients lead to essential redistribution of the stress—strain state.Ukraine Transportation University, Kiev, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 2, pp. 192–199, March–April, 1997.     

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     

Removing "silver" type microcracks in polymethyl methacrylate glass by dry friction

"Silver" type microcracks in polymethyl methacrylate are self-removed on aging. Dry friction can assist in their accelerated removal; by intensifying relaxation processes and causing flow in the surface layer of the polymer, it is able to restore both the polymer structure in the zones of "silver" type microcracks and also to age obvious microcracks. The restored polymer quality is stable. Dry friction raises the resistance of polymethyl methacrylate to splitting in failure.Lenin Civil Aviation Engineering Institute. Translated from Mekhanika Polimerov, No. 3, pp. 465–470, May–June, 1970.     

Cold flow and melting of plastics under severe friction conditions

Dry friction of a series of crystalline polymers (polypropylene, nylon, PTFE) against steel over a wide range of sliding velocities (4.4–4.4×10^–4 cm/sec) and loads (P=7.5–360 kg) with almost complete mutual overlap of the friction surfaces is studied. It is shown that friction of polymer materials against steel may be accompanied by melting of the crystalline polymer (at high velocities) or cold flow (at low velocities) in the surface layers associated with an orientation effect and the appearance of anisotropy.Mekhanika Polimerov, Vol. 1, No. 5, pp. 95–100, 1965     

Static friction of metal - polymer pairs under vacuum conditions

The static friction of a series of polymer — steel friction pairs has been investigated as a function of the stationary contact time at temperatures from –150°C to +200°C. The experimental technique is described and the results of the experiments are evaluated.Novocherkassk Sergo Ordzhonikidze Polytechnic Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1065–1069, November–December, 1970.     

The transfer mechanism in polymer friction

The process of material transfer in polymer friction has been investigated. The effect of the molecular and supermolecular structure of the polymer on the kinetics of the process is examined.Institute of Mechanics of Metal-Polymer Systems, Academy of Sciences of the Belorussian SSR, Gomel'. Translated from Mekhanika Polimerov, No. 4, pp. 668–672, July–August, 1973.     

Study of the strength and coefficients of friction of metal-containing polymers based on heteropolyacids

The strength and coefficients of friction of new heat-resistant composite materials consisting of metallopolymers of iron and cobalt based on molybdosilicic and tungstosilicic heteropolyacids have been studied. It has been established that the use of a lubricant in the frication of metallopolymers over steel brings about a sharper deerease in the coefficients of friction than in the case of the friction of the compact material; this is due to the ability of the metallopolymers to absorb the lubricant material.Kiev Automobile-Road Institute. Translated from Mekhanika Polimerov, No. 5, pp. 931–933, September–October, 1973.     

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.     

Friction properties of highly elastic materials at high contact pressures

A newly designed high-pressure tribometer has been employed to investigate the pressure dependence of the friction force of SKN-40 crosslinked butadiene-nitrile rubber in contact with a steel surface on the pressure range to 1200 kgf/cm² (20°C). Over the entire range of contact pressures the friction process is molecular-kinetic in nature and characterized by a linear dependence of the friction force on the logarithm of the sliding velocity. In the region of normal pressures up to 200 kgf/cm², where the effect of pressure on the friction force reduces to the formation of the actual contact area, the friction constant (proportionality factor relating the friction force and the actual contact area) is practically independent of the pressure. At pressures above 200–300 kgf/cm² the increase in the friction force at fixed actual contact area is attributable to the effect of pressure on the friction constant. The nature of this effect is related not with an increase in the chain-surface interaction energy (the activation energy does not increase), but with an increase in the forces of adhesion owing to the greater number of polymer chain-steel surface contacts on the actual contact area (increase in contact density).Lenin Moscow State Pedagogical Institute, Laboratory for Problems of Polymer Physics. Translated from Mekhanika Polimerov, No. 1, pp. 140–146, January–February, 1971.     

Investigation of the friction of rubber under constant compressive strain conditions at low pressure

A vacuum tribometer was developed which was used to investigate the maximum friction force occurring at the initial instant of slipping in rubber-metal friction pairs under conditions of a given (from 5 to 40%) compressive strain at a low pressure in the temperature range from +100 to –100°C. Filled rubbers on a base of nitrile-butadiene rubbers were studied. Up to the glass transition temperature T_g the vacuum had practically no effect on the maximum friction frocef _m; at temperatures T_g and lower the values off _m obtained in a vacuum were 10–15% higher than those obtained in the atmosphere. It is shown that with a decrease of temperature from 20°C to the glass transition temperature T_g the slope of the dependence of the maximum friction force on the degree of deformation increases, and below T_g decreases. The effect of the slipping speed v on the maximum friction forcef _m was also studied.Laboratory of Polymer Physics, V. I. Lenin Moscow State Pedagogical Institute. Leningrad Branch, Scientific Research Institute of the Rubber Industry. Translated from Mekhanika Polimerov, No. 3, pp. 486–492, May–June, 1970.     

Some features of the frictional behavior of polymeric crystalline materials

The coefficients of friction for thin polymeric films are calculated, and it is shown that the coefficient of friction of the films is much less than that of a homogenous block. This may be due to some features of the antifriction properties of polymeric crystalline materials.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1053–1058, November–December, 1972.     

Low-frequency internal friction in complex composite strands

Conclusion A method was proposed which makes it possible to study the low-frequency internal friction of complex fibers. This method was used to study the internal friction of complex composite fibers based on PCA and PE. We observed a relaxation process which is typical of the composite and is absent in the pure materials.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 11–15, January–February, 1989.     

The design of low-wear friction materials

The relation between the elastoplastic characteristics of the friction surface and contact pressure is analyzed on the basis of the molecular-mechanical theory of friction. A criterion for predicting certain physico-mechanical properties necessary to ensure high wear resistance over a broad temperature interval is proposed.State Scientific-Research Institute of Machine Science, Moscow. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 298–302, March–April, 1969.     

Effect of liquid media on the deformation of the surface layers of a polymer-metal pair in sliding friction

The relation between the high-elastic component of polyurethane deformation and the deformation of the surface layers of metals has been investigated for sliding friction in various media. The surface layers of polymer and metal are plastically deformed. There is a certain correlation between the coefficient of friction and the amount of deformation.Kiev Institute of Civil Aviation Engineers. Translated from Mekhanika Polimerov, No. 1, pp. 147–149, January–February, 1970.     

Maximum force of friction in rubber-metal friction pairs under conditions of constant compressive deformation of the rubber

The maximum force of friction at the initial moment of slip has been investigated on rubber-metal friction pairs under conditions of constant compressive deformation of the rubber during transition from the high-elastic to the glassy state. Filled butadiene-nitrile rubber compounds were studied in the temperature range from +20 to –50°C. The temperature dependence of the maximum force of friction has a sharply expressed maximum near the glass transition temperature. As the temperature falls, the force of friction at first increases, in accordance with the molecular-kinetic theory. As the temperature continues to fall, in the transition region the maximum force of friction begins to rise more sharply owing to a sharp increase in the volume-mechanical friction component. The fall in the maximum force of friction below the glass transition point associated with a decrease in the deformed volume of rubber due to shrinkage and with the reduced mechanical loss factor.Mekhanika Polimerov, Vol. 3, No. 3, pp. 533–538, 1967     

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.     

Experimental study of the effect of friction and bending on the strain distribution around the perimeter of a glass-reinforced plastic ring with unidirectional structure

The effect of friction and bending on the circumferential strain distribution in glass-reinforced plastic rings with unidirectional structure, stretched by two rigid half-disks, has been experimentally investigated. Strain distribution curves for rings of various thicknesses are given. The strain distribution at different levels over the thickness of the ring and the change in compressive strain along the radius have been studied.Institute of Chemical Physics, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 947–949, September–October, 1971.     

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.     

Friction and rheological properties of resin-impregnated glass tape

The dependence of the dynamic coefficient of friction of resin-impregnated glass tape on the sliding speed over the mandrel surface and the viscosity of the resin is derived. The formulas obtained are confirmed by the results of experiments which indicate a linear dependence of the coefficient of friction on the sliding speed of the tape over a metal mandrel. Graphically, this dependence is expressed by straight lines with a common origin and a slope that increases with the viscosity of the resin. The coefficient of friction of glass tape sliding over a prewound layer at low speeds also has a linear dependence. At high speeds the dependence takes the form of a damped curve.Translated from Mekhanika Polimoerov, No. 1, pp. 166–170, January–February, 1976.     

Polyformaldehyde as an antifriction material

The antifriction properties of polyformaldehyde have been studied on the velocity interval from 4 · 10^–4 to 10 m/sec and at loads to 300 kgf/cm². Tests were conducted with and without lubrication on laboratory friction machines of various types and under service conditions. Steel, emery cloth, and polyformaldehyde were used as the second member of the friction pair. The values of the coefficients of friction, temperatures and performance limits for polyformaldehyde are compared with those for polycaprolactam.All-Union Scientific Research Institute of Railroad Transport, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 850–856, September–October, 1969.