Three-dimensional reinforced fabric materials

Three-dimensional materials whose principle of construction is based on marked curvature of the fibers of multilayered three-dimensionally woven fabric are discussed. The effect of the law and degree of curvature of fibers on the deformative properties of the composite material is investigated on the basis of the model proposed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 311–318, March–April, 1970.     

Theoretical and maximum attainable strength of various uniaxially oriented polymers (film,fibers)

The theoretical strength of various ideally oriented synthetic fibers was calculated. The calculation was based on an assumption that the rupture of polymers involves simultaneous breaking of molecular chains and pulling asunder the chain ends. The temperature-time dependence of the strength of fibers was analyzed and the maximum attainable strength of fibers of various kinds was calculated to show that it is 2–5 times higher than that recorded in practice. The main causes of the difference between the attainable and attained levels of strength are associated with imperfections of the supermolecular structure and an insufficient degree of orientation of materials of this kind. The principal means of obtaining high strength levels of synthetic fibers were discussed.Mekhanika Polimerov, Vol. 2, no. 6, pp. 845–856, 1966     

Effect of hot-drawing conditions on the orientation characteristics of carbon-chain fibers determined by the acoustic method

The orientation characteristics of polypropylene, polyacrylonitrile, and chlorinated PVC fibers, determined by the acoustic method, have been investigated in relation to the fiber drawing conditions (draw ratio, speed, and temperature). It is shown that there is a correlation between the mechanical characteristics and the degree of acoustic anisotropy.Tashkent Institute of the Textile and Light Industries. Translated from Mekhanika Polimerov, No. 3, pp. 552–554, May–June, 1971.     

Temperature dependence of the mechanical properties of oriented kapron fibers crosslinked with formaldehyde

Comparative regions of effective performance of oriented kapron fibers crosslinked with various amounts of formaldehyde are obtained on the basis of tensile test data in a broad temperature interval. As the degree of crosslinking increases, the region of softening of the crosslinked fibers is displaced in the direction of higher temperatures.Mekhanika Polimerov, Vol. 4, No. 2, pp. 304–308, 1968     

Effect of surface treatment of carbon fibers on the strength properties of carbon fiber plastics

Conclusions The strength characteristics of composites based on carbon fibers having a coating of silicon carbide are in direct dependence on the coating thickness and on the porosity, which makes it possible to assume the possibility of increasing the degree of realization of the strength characteristics of fibers having a coating in a composite by increasing the degree of impregnation of the carbon cord with the binder. The latter finds confirmation also in the fact that at a small coating thickness on the carbon fiber (of the order of 5 nm) the porosity of the composite obtained is equal to the porosity of the material based on the carbon fiber without coating. Moreover, as is evident from Fig. 3c, the casing of silicon carbide does not form a continuous coatting over the whole perimeter of the cord. The presence of these prerequisites, and also the high resistance of carbon fibers having a silicon carbide coating to oxidation [9], open up wide prospects for creating new composite materials based on them.Translated from Mekhanika Kompozitnykh Materialov, No. 4, pp. 603–606, July–August, 1979.     

Effect of thermal treatment temperature on the structure and properties of carbon fibers

Conclusions 1. It has been shown that the presence of a maximum in the dependence of strength on Young's modulus for carbon fibers made from PAN fiber may be explained by an effect of the process of temperature stress accumulation which takes place under the conditions of isometric heating. The start of this process, which causes a rearrangement of the internal structure of the high-modulus fiber, coincides with the start of the anomalous rise in fiber density.2. The interconnection between surface and internal defects and the elastic-strength properties of carbon fibers made in the temperature treatment range 600–3000°C has been studied.3. Original data on the elastic-strength properties of borided carbon fibers have been obtained; the structure of these is marked by a high degree of perfection. It has been shown that in boriding, which facilitates graphitization of the carbon, the process of regular reduction in fiber strength which is reached in the precrystallization stage is somewhat retarded.All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1036–1042, November–December, 1976.     

Effect of the crosslink density of elastic polyurethane fibers on their mechanical properties

The effect of the nature of the bonds and the degree of crosslinking on the properties of elastic polyurethane fibers has been investigated in relation to various fiber treatments. The fiber properties are mainly determined by the chemical bonds, the proportion of which should be not less than 40%.Leningrad Branch, All-Union Scientific-Research Institute of Artificial Fibers. Kaunas Artificial Fiber Plant. Translated from Mekhanika Polimerov, No. 3, pp. 515–516, May–June, 1976.     

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     

Comparative analysis of the structural order and defectiveness of reinforcing fibers on the basis of normalized values of mechanical properties

Experimental data on mechanical properties referred to their limiting values for a flawless polymer crystal with long molecular chains is used in a comparative analysis of the degree of ordering of the structure (crystallinity, orientation) and the defectiveness of the reinforcing fibers. The actual elastic moduli and limiting (theoretical) elastic modulus are used to obtain coefficients that characterize the overall order of the structure of the fibers but are independent of their defectiveness. Values of true strength in tension and the limitingly attainable or theoretical strength are used to calculate conditional coefficients that depend both on the overall order and the defectiveness of the fiber structure. The difference in the coefficients makes it possible to detect dangerous local defects that lead to fiber failure. Results are presented from calculations for more than 20 types of reinforcing fibers. Despite the approximate nature of these representations, the data that is obtained permits comparisons of different types of fibers, characterization of their quality, and evaluation of the degree of perfection of the fiber production technology.Paper presented at the IX International Conference on the Mechanics of Composite Materials, Riga, October, 1995.St. Petersburg State University for Technology and design, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 32, No. 4, pp. 444–453, July–August, 1996.     

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.     

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.     

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.     

A study of the causes of the reduced strength of glass-reinforced phenolformaldehyde plastics

A study of the curing kinetics of phenolformaldehyde resin in the presence of glass and quartz has shown that one of the chief causes of the reduced strength of glass-reinforced plastics based on phenol-formal-dehyde resin is the difference in the rate and degree of cure in layers close to the fibers and in the bulk of the resin. This is caused by the presence on the surface of the fibers of a hydrate sheath with increased concentration of hydroxyl ions and by the presence of hydrogen bonds between the oxyphenyl groups of the resin and the silanol groups on the surface of the fibers. Chemical treatment of the glass fibers has the effect of diminishing those factors responsible for the reduced rate and degree of cure, and in spite of the lower surface energy of the fibers, the strength of the glass-reinforced plastic increases.Mekhanika Polimerov, Vol. 1, No. 3. pp. 8–14, 1965     

Effect of modifying additions on the physicomechanical properties of composites based on polyethylene and wastes from linen yarn production

This article examines the feasibility of using coupling agents to alleviate the shortcomings characteristics of materials that contain natural fibers: low water resistance and a high degree of heterogeneity. A determination is made of the effect of additions of polyisocyanate and stearic acid on the fluidity of the melts and the strainstrength properties and water resistance of polyethylene composites containing mixtures of wastes from linen yarn production. It is shown that an addition of stearic acid significantly improves the dispersion of fibers in the composites, which in turn leads to a reduction in melt fluidity and an increase in elastic modulus in the high-filler-content region compared to composites that do not have additions of stearic acid. Additions of polyisocyanate appreciably increase the strength and water resistance of the given composites.Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 4, pp. 540–547, July–August, 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.     

Modification of the mechanical properties of synthetic fibers by grafting vinyl monomers

Graft polystyrene has been synthesized on polypropylene fibers. The isometric heating curves of the grafted fibers have two maxima. The first is associated with the preserved oriented polypropylene structures, the second with the oriented structures formed directly in the process of polystyrene synthesis. The maximum stress corresponding to the latter maximum is proportional to the amount of polystyrene and the degree of orientation of the starting polypropylene and depends on the mechanical stress in the fiber during the process of polystyrene synthesis.Mekhanika Polimerov, Vol. 3, No. 6, pp. 963–969, 1967     

Effect of residual stresses on the strength of oriented glass-reinforced plastics

The effect of structural residual stresses on the strength of a glass-reinforced plastic loaded along and across the fibers is investigated. It is established that the residual stresses lead to an increase in the strength of the glass-reinforced plastic across the fibers and to cracking of the polymer matrix in tension along the fibers, but have practically no effect on the combined deformation of the matrix and the fibers in compression.Moscow Ordzhonikidze Aviation Institute. Translated from Mekhanika Polimerov, No. 3, pp. 475–480, May–June, 1969.     

Quantitative evaluation of the brittleness of carbon fibers

A simple method is proposed for the rapid determination of the brittleness of fibers. Measurement data are given for glass and carbon fibers. It is shown that the conditions of heat processing for carbon fibers may fundamentally alter their brittleness.A. F. Ioffe Physical-Engineering Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 950–952, September–October, 1973.     

Interaction of a polymer matrix and short reinforcing fibers

A model of a glass-reinforced plastic with short unidirectional fibers is proposed. The distribution of tensile stresses in the polymer matrix and the fibers and the shear stress distribution at the interface in uniaxial tension are investigated in the elastic formulation.Riga Polytechnic Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1030–1035, November–December, 1971.     

Effect of the structure of a fibrous layer on its permeability for a nonlinearly viscous fluid

The solution of the problem of the percolation of a nonlinearly viscous (with a power flow law) fluid through unit cells is used to find the dependence of the permeability coefficient of a unidirectional layer of fibers on fiber concentration, parameters characterizing the location of the fibers, and the parameters of the fluid (the exponent in the flow law) for random and regular fiber configurations in the transverse plane. It is established that the degree of nonuniformity of the pore space of the layer has a significant effect on its permeability and that this effect increases with an increase in the nonlinearity of the fluid. Data from a model experiment and computer simulation are used to describe the mechanism of transformation of the pore space by the fluid front. It is shown that consolidation of the layer also affects its permeability.Belarus State Technological University (Minsk, Belarus). Translated from Mekhanik Kompozitnykh Materialov, Vol. 33, No. 4, pp. 554–563, July–August, 1997.