Study of the effect of the dressing of carbon fibers on the properties of carbon-fiber-reinforced plastics based on polyacetals

Studies are made of the mechanical and friction engineering properties of a copolymer of trioxane-1,3,5 with dioxolan-1,3 reinforced with dressed carbon fibers based on hydrated cellulose. Polyalkyloxysilanes are used as the finishes. The optimum concentrations of the finishes on the fibrous filler are determined. Relations are obtained to describe the dependence of the mechanical properties of carbon-fiber-reinforced plastics on the type of finish and its effect on the condition of the phase boundary between filler and the polymer matrix. The effect of adhesion of the polymer to the fibrous filler on the properties of a randomly reinforced thermoplastic composite is also determined. The dependences of the friction engineering properties of polyacetal-based carbon-plastics on the loading parameters of the friction-loading unit are examined. The material that is developed has high values of strength, elastic modulus, and notch toughness and low values of the friction coefficient and shrinkage. The material can be used as structural and anti-friction elements in rocketry, aviation, and the automobile industry.Ukrainian State Chemical Engineering University, Dnepropetrovsk. Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 90–97, January–February, 1997.     

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.     

Polypropylene reinforced with aramid and glass fibers

The effect of the chemical nature of the aramid fibers Phenylone, Terlon, Armos, and SVM on the mechanical, thermophysical, and antifriction properties of reinforced polypropylene was investigated. It was found that the composite filled with SVM fibers based on a stiff-chain polymer has high tensile strength and bending modulus. Reinforcement of polypropylene with Phenylone stiff-chain fibers produces a composite with a high impact viscosity. Organoplastics based on polypropylene and aramid fibers have a low density and friction coefficient and high durability. Reinforcement of polypropylene with aramid (SVM) and glass fibers increases the technological properties of the composites. The glass-filled organoplastics developed can be used in instrument making, radio engineering, and machine building as antifriction and construction materials.Ukrainian State Chemical Technological University, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 106–110, January–February, 1996.     

Mechanical properties of carbon fibers coated with refractory carbides

The internal friction method has been used to investigate the protective function of barrier coatings of silicon and zirconium carbide. The effect of the thickness of the coating on the mechanical characteristics of carbon fibers and their oxidation resistance is examined. The optimal coating thickness is established. A surface hardening effect of the coatings has been detected.Voronezh Polytechnic Institute, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 536–538, May–June, 1976.     

Physico-mechanical properties of polymer materials and the friction problem

Aspects of the friction behavior of polymer materials associated with their molecular structure and responsible for the relatively small value of the modulus of elasticity as compared with the ultimate strength are examined. It is shown that, in view of the important influence of hydrostatic pressure on the mechanical properties of polymer materials, the mechanical characteristics obtained from uniaxial testing cannot be used in calculating the contact area and the forces of friction. Formulas are presented for calculating the mechanical characteristics under these conditions. The results of indentation experiments designed to simulate contact processes are discussed. It is shown that the resistance to deformation of the asperities on the surface of polymer materials is of the order of the yield stress, and not two or three times greater, as with metals. The results of contact creep studies are described and evaluated. The results of investigations of the mechanical and antifriction properties of filled polymer materials show that the forces of friction are inversely proportional to the modulus of elasticity, while the thermophysical characteristics are a function not only of the thermophysical characteristics of the filler and the base, but also depend to a great extent on the shape of the filler particles; thus, when a fibrous filler with a low coefficient of linear expansion is used, the thermal stability of the friction material can be considerably improved. The results of a study of the adhesion interaction of polymer materials under conditions of omnidirectional nonuniform compression and simultaneous deformation are presented. It is shown that the adhesion interaction is strong even at room temperature. Aspects of the mechanical properties of lubricants that determine their effectiveness in polymer friction are considered.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 303–314, March–April, 1969.     

Effect of combined extrusion parameters on mechanical properties of basalt fiber-reinforced plastics based on polypropylene

Basalt fibers are efficient reinforcing fillers for polypropylene because they increase both the mechanical and the tribotechnical properties of composites. Basalt fibers can compete with traditional fillers (glass and asbestos fibers) of polypropylene with respect to technological, economic, and toxic properties. The effect of technological parameters of producing polypropylene-based basalt fiber-reinforced plastics (BFRPs) by combined extrusion on their mechanical properties has been investigated. The extrusion temperature was found to be the main parameter determining the mechanical properties of the BFRPs. With temperature growth from 180 to 240°C, the residual length of the basalt fibers in the composite, as well as the adhesive strength of the polymer-fiber system, increased, while the composite defectiveness decreased. The tensile strength and elastic modulus increased from 35 to 42 MPa and 3.2 to 4.2 GPa, respectively. At the same time, the growth in composite solidity led to its higher brittleness. Thus, a higher temperature of extrusion allows us to produce materials which can be subjected to tensile and bending loads, while the materials produced at a lower temperature of extrusion are impact stable. The effect of the gap size between the extruder body and moving disks on the mechanical properties of the BFRPs is less significant than that of temperature. An increase of the gap size from 2 to 8 mm improves the impregnation quality of the fibers, but the extruder productivity diminishes. The possibility of controling the properties of reinforced polypropylene by varying the technological parameters of combined extrusion is shown. The polypropylene-based BFRPs produced by the proposed method surpass the properties of glass and asbestos fiber-reinforced plastics.Submitted to the 10th International Conference on Mechanics of Composite Materials (Riga, April 20–23, 1998).Ukrainian State University of Chemical Technology, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 6, pp. 845–850, November–December, 1997.     

Effect of structural changes on the sorptivity and mechanical properties of polyformaldehyde fibers

The dependence of the mechanical and sorption properties and structure of polyformaldehyde fibers on the degree of extension has been investigated. By x-ray structural analysis and sorption techniques it is shown that an increase in stretch ratio is accompanied by an increase in structural orientation with a simultaneous increase in porosity. It is established that the change in the mechanical properties associated with drawing depends both on orientation and on the presence of macrodefects in the fiber.Kiev Technological Institute of Light Industry. Translated from Mekhanika Polimerov, No. 6, pp. 1103–1106, November–December, 1971.     

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.     

Polymer friction

The results of research on the antifriction properties of polymeric materials and expressions for calculating their coefficient of friction are presented. The effect of the mechanical properties of the materials on their antifriction characteristics is discussed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 421–429, May–June, 1975.     

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 preliminary orientation on polymer friction

It has been shown experimentally that preliminary orientation leads to a change in the mechanical properties of polymers, a decrease in the actual contact area and a corresponding reduction of the deformation and adhesion components of the forces of friction.Institute of Mechanics of Metal — Polymer Systems, Academy of Sciences of the Belorussian SSR, Gomel'. Translated from Mekhanika Polimerov, No. 4, pp. 692–696, July–August, 1971.     

Effect of annealing temperature on the mechanical properties of polyethylene terephthalate fiber

The mechanical properties of polyethylene terephthalate fibers stretched at 45 and 110° C have been investigated in relation to annealing temperature. It is shown that for fibers with the maximum degree of stretch the annealing temperature has no effect on mechanical strength. Reduction in the stretch of the fibers leads to an increase in strength upon annealing, and this may be associated with densification of the amorphous zones due to the formation of a large number of intermolecular bonds between the links of the polymer chains.Mekhanika Polimerov, Vol. 3, No. 3, pp. 503–506, 1967     

Temperature dependences of internal friction and shear modulus in glass-textolites irradiated with electrons

A study is made of mechanical relaxation mechanisms and the correlation between parameters characterizing the temperature dependence of internal friction and shear modulus when the mechanical and electrical properties of glass-textolites of grades ST-11 and ST-ETF are altered by exposure to different doses of high-energy electrons. High-temperature - and -transformation are observed, these transformations being due to the unfreezing of segmental mobility in the polymer matrix and the boundary layers at the surfaces of the glass fibers under the influence of the radiation. A discussion is presented of features of radiation-induced degradation processes in the polymer binder and at points where it contacts the filler. The data that is obtained shows that glass-texolites ST-ETF and ST-11 are highly resistant to radiation.Scientific-Research Institute of Experimental and Theoretical Physics of Kazakh State National University, Almaty, Kazakhstan. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 4, pp. 548–553, July–August, 1997.     

Strength of boron fibers

The tensile and flexural strength and elastic properties of continuous boron fibers 95–105 µ in diameter obtained by depositing boron on a tungsten filament 10–12 µ in diameter have been investigated. The strength properties are primarily determined by the defects present at the boron sheath-core interface and for the fibers investigated have a limit of approximately 400 kgf/mm². Coarse surface or internal defects are capable of reducing the strength of the fibers to 200–250 kfg/mm².All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1126–1127, November–December, 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     

Comparison of methods of investigating the components of the elongation of textile fibers

Resolving the elongation of textile fibers into its components (rapidly disappearing, slowly disappearing, and residual) provides valuable information on the mechanical properties and makes it possible to predict a series of mechanical characteristics of the fabrics into which they are made. The optimal methods of determining these components are established.Moscow Textile Institute. Translated from Mekhanika Polimerov, No. 3, pp. 444–450, May–June, 1972.     

Measuring the stresses in fibers of a loaded composite material by the method of infrared spectroscopy

Conclusions 1. Actual stresses in reinforcement fibers of a loaded composite have been measured by infrared spectroscopy.2. It has been shown that the plain rule of mixtures, not accounting for changes in mechanical properties of the matrix during processing of a composite, does not apply to a hot molded polyethylene-polypropylene composite.3. It is suggested that around the reinforcement fibers there exists an ordered layer of the matrix material capable of carrying a heavy load. A method is proposed, furthermore, for calculating the mechanical characteristics of the composite with such a layer. The volume fraction and the thickness of this hardened layer have been estimated from experimental data.Paper presented at the Third All-Union Conference on Polymer Mechanics in Riga, 1976.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 832–837, September–October, 1977.     

Intermolecular interactions in fiber-forming linear polymers and certain of their mechanical properties

Values of the specific volumetric intermolecular interaction energies of a series of linear polymers have been calculated on the basis of data on the interatomic and intermolecular interactions of the functional groups in the polymer molecules. It is shown that the specific volumetric intermolecular interaction energy is closely correlated with the elastic and relaxation properties of the polymers, which makes it possible to predict a series of mechanical properties of chemical fibers.Leningrad Branch, All-Union Scientific-Research Institute of Synthetic Fibers. Translated from Mekhanika Polimerov, No. 5, pp. 790–795, September–October, 1971.     

Structural stresses in composites reinforced with a system of anisotropic fibers

The effect of the anisotropy of the mechanical and thermophysical characteristics of the reinforcement on the temperature stresses in unidirectional composites has been investigated. The stresses near fibers forming a regular structure in the transverse plane are estimated as a function of the thermoelastic properties of the components and the structure parameters.Moscow Power Engineering Institute. Translated from Mekhanika Polimerov, No. 4, pp. 728–731, July–August, 1974.     

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