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.     

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.     

Investigation of the elastic properties of friction plastics with ultrasound

Using data on the rate of propagation of longitudinal vibrations and the dynamic Young's modulus, we studied two-component friction plastics over the temperature range 20–150°C by an ultrasonic pulse method at a frequency of 1 Mc. The changes in acoustic characteristics were investigated in relation to the degree of vulcanization, plasticization and polarity of rubber at 20°C.Mekhanika Polimerov, Vol. 1, No. 2, pp. 152–158, 1965     

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     

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     

Rubber wear during friction against a metallic surface (with reference to packing glands for high-speed machine elements)

The wear of rubber in sliding against a metallic surface at high sliding velocities, which causes temperatures at the point of contact of the order of 100–250°C, has been studied. The theoretical equation obtained relates the wear of rubber during sliding against a metallic surface to its elastic-strength and friction properties and to the geometrical characteristics of the metal surface. Satisfactory agreement between theory and experiment is found.Mekhanika Polimerov, Vol. 1, No. 6, pp. 120–126, 1965     

Modification of glass-filled polyamide 66 by reactive oligoorganosilane

Properties of glass-filled polyamide 66 modified by reactive oligoorganosilane were investigated. It was found that modification led to the improvement of the rheological properties of polyamide. The addition of the modifier decreased the glass transition temperature T_g of the polyamide from 60 to 50–59°C, without affecting the melting point. Composites modified by oligoorganosilane are characterized by higher (10–40°C) temperatures of onset and 50% weight loss as compared to the initial composite. It was found that chemical reaction of oligoorganosilane with polyamide and glass fibers took place during coextrusion of the modifier and polyamide, which formed firm chemical bonds between the polyamide and filler and thus favored a considerable improvement in the physicomechanical properties of the composite. The change in the structure and properties of the polyamide observed during modification by oligoorganosilane significantly affected its behavior during friction. The modification made it possible to increase the wear resistance of the composite 1.5 to 2 times and to decrease its friction coefficient from 0.38 to 0.27–0.33. It was also found that the ability of oligoorganosilane to react during its processing with water in the polyamide allowed for a significant decrease in the intensity of hydrolytic processes in the polymer. Because of this, the physicomechanical, rheological, and antifrictional properties of modified composites with an increased content of moisture (up to 3%) in the initial polyamide surpass similar characteristics of the composites containing no modifier, with not only enhanced but also optimum (0.2%) humidity of polymer granules.Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 4, pp. 545–553, July–August, 1998.     

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.     

Effect of temperature on the mechanical properties of boron fibers

The effect of exposure to temperatures on the interval 20–600°C for up to 1000 h on the physicomechanical properties of boron fibers at room temperature has been investigated. Prolonged exposure to temperatures up to 200°C does not have much effect on the mechanical characteristics of the fibers, whereas heating for one hour at 300–350°C increases the strength of the fibers by 10–12%.All-Union Scientific Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 329–332, March–April, 1971.     

Effect of temperature on the nature of the tear surface of styrene polymers

The tear surfaces of polystyrene and SKS-85 butadiene-styrene copolymer (85% styrene) have been investigated at temperatures from –45 to +100°C and from –60 to +40°C, respectively. The fracture surface of these polymers changes not only on transition from the glassy to the high-elastic state, but also within the glassy state itself, changes being observed both in the relative extent of the individual zones contributing to the fracture surface and in the nature of those zones. Changes in the nature of the fracture surface associated with a slowing of the fracture process occur at 0 and 40°C in the case of polystyrene and at –10°C in the case of copolymer SKS-85 and are attributable to secondary transitions in the polymers.Moscow Technological Institute of the Meat and Dairy Industry. State Institute of Polymer Adhesives, Kirovakan. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 257–264, 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.     

Behavior of filled polyphenylquinoxalines during friction

Conclusion 1. It has been established that, as the chain of polyphenylquinoxalines becomes more rigid by addition of aromatic nuclei of the naphthylimide group to the macromolecule part, the wear resistance of graphite-filled polymer systems increases.2. It has been demonstrated that during friction with filled polyphenylquinoxalines in the polymer binder there occur complex destructive-structurizing processes whose penetration depth is determined by the chemical constitution of the selected polymers.3. It has been established that in the rigid-chain polyphenylquinoxaline during friction at high temperatures, just below the glass-transition point but within the range of faster relaxation processes, the destructive-structurizing processes abate and then at temperatures above 250°C active gelling occurs.Institute of Heteroorganic Compounds, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1049–1054, November–December, 1978.     

Polymer fractography and fracture kinetics

The fractographic method makes it possible to determine the test temperature and time at which anomalies appear in the temperature-time dependence of the strength of polymethyl methacrylate and polycaprolactam by finding the conditions of disappearance of specular zones from the fracture surfaces of these polymers. For PMMA these values are –40°C and 10^–2 sec, for PCL –120°C and 10^–7 sec, respectively.For communication 1 see [2].Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 232–237, March–April, 1971.     

A study of the physicomechanical properties of carbon fibers at high temperatures

Conclusions 1. Carbon fibers, similar to graphite materials, are heat-resistant and do not Iose their short-term tensile strength in the temperature range studied — 20 to 2000°C.2. Young's modulus of carbon fibers hardly changes in the temperature range 20 to 1200°C, but a significant decrease is observed upon a further increase in temperature.Translated from Mekhanika Polimerov, No. 4, pp. 626–630, July–August, 1977.     

Some laws of plastics friction

The dependence of the actual contact area S of plastics on temperature, specific load, and sliding speed has been investigated. The value of S increases exponentially with the specific load, the maximum value at large specific loads being less than the nominal contact area. The temperature dependence of S under static conditions between 20 and 130° C is attributable to the decrease in the static modulus of elasticity of the plastic near the glass transition point and to the development of high-elastic and plastic deformations at elevated temperatures. There is practically no change in S as the sliding speed varies from 10^–3 to 10 cm/min; at the same time the force of friction increases slightly.Mekhanika Polimerov, Vol. 3, No. 6, pp. 1078–1081, 1967     

Reversible changes in the adhesion of polymers to solid surfaces

The adhesion properties of coatings of polycrystalline hexafluoropropylene—vinylidene fluoride copolymer on steel and glass have been investigated. Coatings formed at 200–240° C suffer a reversible loss of adhesion following the diffusion of water and acid molecules to the interface, which is attributable to the mobile adsorption-desorption nature of the adhesion of this particular copolymer to steel and glass. Heat treatment at 280° C gives the coating improved resistance to the debonding action of water.Ural Scientific-Research Chemical Institute, Sverdlovsk. Moscow Institute of Fine Chemical Technology. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1065–1070, November–December, 1968.     

Regulation of the mechanical properties of thermoplastic carbon fiber-reinforced plastics by changing their production conditions and surface treatment of the fibers

The effect of technological parameters of processing and surface treatment of carbon fibers on the mechanical properties of carbon fiber-reinforced plastics (CFRPs) was investigated. The copolymer of 1,3,5-trioxane with 1,3-dioxolane was used as the polymer matrix, and medium-modulus hydrated cellulose Ural LO-24 carbon fibers served as the reinforcing filler. The polymer matrix was mixed with the carbon fibers by the method of combined extrusion. The dependence of the mechanical properties of CFRPs on the technological parameters of screw-disk extrusion was studied. It was found that the properties of the composites were greatly affected by the size of the working disk gap, the disk rotation rate, and the temperature in the zone of normal stresses. The surface of the carbon fibers was activated with atmospheric oxygen in the temperature range of 450–600°C, with mass loss of the fibers no greater than 3–4%. A 30–40% increase in the mechanical properties of the CFRPs was achieved. A decrease in the melt index of the 1,3,5-trioxane copolymer with 1,3-dioxolane reinforced with oxidized carbon fibers was observed, which should be taken into account in processing the composites into products. Introduction of carbon fibers in the 1,3,5-trioxane copolymer with 1,3-dioxolane allows us to increase the wear resistance and decrease the friction coefficient, which makes it possibile to use these materials in the friction units of machines and mechanisms, such as plain bearings, gears, and flange packings.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Ukrainian State University of Chemical Technology, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 5, pp. 673–682, September–October, 1998.     

Nature and mechanism of friction of rubberlike polymers in different physical states

We have investigated the frictional properties of crosslinked butadiene-nitrile and butadiene-styrene copolymers and natural rubber in friction against polished steel under vacuum conditions in the temperature interval from –200 to +150° C, which embraces the glassy and high-elastic states, as well as the transition region between them. The temperature dependence of polymer friction is characterized by two maxima, a principal and a low-temperature maximum. The principal maximum, observed in the glass transition region, is not associated with the mechanical loss maximum observed in the polymers themselves. The temperature dependence of the force of friction is composed of three parts. In the high-elastic region there is an increase in the force of friction with fall in temperature, in accordance with the molecular-kinetic theory of friction of rubberlike polymers. In this region the nature of friction is associated with mechanical losses in the surface layer of polymer. The mechanical losses inside the polymer itself are unimportant. The deviation from the theoretical curve and the fall in the force of friction below a certain temperature in the transition region are chiefly associated with a decrease in the actual area of contact as the polymer passes into the glassy state. In the glassy region the friction is significantly determined by the mechanical losses in the polymer itself associated with the repeated elastic and forced-elastic deformation of the asperities in the layer of polymer in contact with the rigid surface. Therefore the low-temperature maximum is closely related to the mechanical loss maximum observed in the same temperature region in dynamic tests. Apart from this, the friction maximum is also associated with the increase in the forces of adhesion and the reduction of the actual area of contact at temperatures at which a forced-elastic mechanism of compression of the polymer asperities is not realized.Mekhanika Polimerov, Vol. 3, No. 1, pp. 123–135, 1967     

Thermal effects in a glass laminate in tension

The results of a calorimetric investigation of a glass-reinforced textolite in uniaxial tension are presented. The specimens were deformed on the interval of strain rates from 0.3 to 10.5 mm/min at test temperatures from –30 to 80°C. The thermal effects are shown to depend on strain rate and test temperature.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 599–604, July–August, 1971.     

Properties of multicomponent polymers systems

In order to design materials having different mechanical properties combined with a permittivity of 2.2–2.6 and tg =2·10^–4-4.10^–4 at 20±1° C and 10⁶ Hz, it is possible to use compositions consisting of polystyrene, polyisobutylene and polyethylene. Projections of the three-dimensional triangular composition-property diagrams are presented for selecting the composition corresponding to spcified properties (hardness at 20 and 50° C and breaking stress and elongation).Central Scientific-Research Institute of Communications, Moscow. Moscow Krupskaya Regional Pedagogical Institute. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 133–1135, November–December, 1968.