The short-term creep and strength of fibrous polypropylene structures are investigated. On the basis of these characteristics, we develop the models of linear and nonlinear viscoelastic deformation of materials, specify the fields of their applicability, and study criteria used for the evaluation of the static strength and durability of these composites.Keywords: short-term creep, static strength, durability, fibrous structures, models of viscoelastic deformation of materials, equations of state.Introduction. Fibrous structures and frames produced according to the technologies used in the textile industry are now more and more extensively applied in various fields of the national economy, namely, in machine building, light industry, transport, civil engineering, materials science (for the development of new composite materials), production of consumer goods, etc. Elements of machine parts and mechanisms produced by using these structures decrease the consumption of materials and the amount energy required for manufacturing the products, improve their functional parameters, increase their reliability and service life, and decrease the cost of production.As source materials for the major part textile structures, it is customary to use polyamide (capron and anid), polyester (lavsan), and staple threads. A thread is a linear combination of fibers (filaments) in the form of a continuous strand whose properties are typical of textile materials, including high tensile strength and flexibility. It may consist of a single fiber or of a family of continuous or discontinuous fibers. To avoid the possibility of sliding of the fibers and form a functional thread, the fibers are twisted or woven.The mechanical properties of threads depend on the properties of fibers or monofibers and the structure of the thread. The serviceability of the thread is determined by the packing density of the fibers, their geometric dimensions, the length of the segment of a fiber between the points of linking, its mobility, and the orientation of fibers about the axis of the thread. The structure of the thread plays the principal role in the mechanism of transformation of the properties of fibers into the properties of the thread.The structure of threads and its influence on the mechanical characteristics of the materials for different types of thermal and force loading were especially comprehensively investigated in [1][2][3][4][5][6][7]. Thus, it was indicated that, for each thread (depending on its design), it is possible to choose the optimal thickness of filaments allowing one to get a substantial improvement of the initial moduli of longitudinal elasticity and shear, ultimate strength, ultimate fracture strain, wear resistance, fatigue strength under multicycle loading, etc.Numerous models were proposed for the prediction of the stress-strain diagrams of twisted threads according to their structure and the mechanical properties of constituents [7]. However, only for systems formed by continuous fibers, it is possible to attain satisfactory a...

The elastic-deformation behavior of unidirectional carbon-fiber-reinforced epoxy laminates is investigated. The effect of operating temperature decrease to 77 K on their deformation and strength is studied. The effectiveness of prediction of stiffness and compliance parameters and load-carrying ability of laminated carbon-fiber-reinforced composites has been analyzed on the basis of mechanical characteristics of the fiber and matrix.Introduction. The demand for higher load-carrying ability of constructions, their higher reliability and longer service life, as well as for smaller weight and material consumption for equipment necessitates the development of new composite materials and a wider use of the existing ones. Remarkable among composite materials are carbon-fiber-reinforced composites. The reasons limiting their use in the engineering practice are the lack of reliable experimental procedures for the determination of mechanical characteristics of reinforced composites, difficulties in the mathematical modeling of deformation processes and evaluation of the load-carrying ability of reinforced structures, and the need for new, more economical manufacturing techniques.The mechanical properties of composite materials are determined by the properties of the constituents, the structure of composites, mode of interaction at matrix-fiber interfaces, and manufacturing technique. Many mechanical parameters of composites can be calculated from known properties of constituents. However, because of the high sensitivity of some parameters (e.g., strength) to the action of many factors, which cannot be fully allowed for, the application of rigorous mathematical solutions is not always possible.The deformation and fracturing behavior of laminated fiber composites is described in numerous papers [1][2][3][4][5][6][7][8]. The most developed branch of the mechanics of heterogeneous media is apparently the branch dealing with the determination of the effective characteristics of composite materials. Expressing mechanical parameters of a composite in terms of characteristics of individual constituents gives ample scope for the design of materials with tailor-made properties. The main advantage of laminated fiber composites is the possibility to give material the anisotropy that is optimal for each particular case of its application.Deformation processes in heterogeneous media were investigated in most cases at room temperature and elevated temperatures. The use of such materials at low or cryogenic temperatures, e.g., in cryogenics or space technology, requires more detailed study of deformation and fracture processes under deep freezing conditions. The aim of the present work was to study the load-carrying ability of unidirectional carbon-fiber-reinforced epoxy laminates under static loading at room temperature and cryogenic temperatures (down to 77 K) and to examine the possibilities of predicting their strength from the structure, volume fraction and mechanical properties of the fibers and matrix.

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The procedures of bearing strength prediction for composite laminates reinforced with high-strength unidirectional fibers at room and cryogenic temperatures are discussed. The best agreement between the calculated and experimental data is observed when the temperature dependence of effective mechanical parameters of plies is allowed for within the framework of the elastic theory of laminated heterogeneous bodies.Introduction. The current tendencies in machine, aircraft, and rocket industries are towards reducing the materials consumption of manufacture while raising the service life and reliability of products. These mutually exclusive requirements can be met by means of novel composite materials. The use of composites in rocket and aircraft structures is among the greatest recent advances in aeronautics and space exploration [1][2][3].Composites, specifically carbon-, glass-, and boron-reinforced laminates, offer a high specific strength and rigidity, a required heat resistance, thermal stability and erosion resistance under various thermomechanical loading conditions. An outstanding example of composites for cryogenic service is a superconducting cable made up of dozens of thousands of fibers embedded in a copper matrix.Properties of composite materials depend on the properties of their components, the component ratios, the interactions at matrix-fiber interfaces, and the manufacturing processes. Many of mechanical parameters of composites can be calculated from the known properties of their components, based on the component ratios, the type of matrix-fiber interactions, and fabrication techniques. However, since some of the parameters, such as strength, are highly sensitive to numerous factors that cannot be fully allowed for, the application of exact mathematical solutions are not always feasible.The deformation and fracture behavior of fiber-reinforced laminates has been addressed in the publications [4][5][6][7][8][9]. Apparently, the section dealing with the determination of effective characteristics of composites should be considered the best elaborated section of the mechanics of heterogeneous media. When expressing mechanical parameters of a composite in terms of characteristics of its individual components, great possibilities are opened up for designing materials with preset properties. The major benefit offered by fiber-filled composites is that a material can be endowed with an optimal anisotropy for each particular application. No optimal combination of thermomechanical and functional characteristics of a composite can be achieved unless reliable and comprehensive experimental evidence of their mechanical behavior in a wide range of temperatures, down to ultra low temperatures, is available.Thermomechanical behavior of unidirectional fiber-reinforced polymer composites has been the objective of much research [10][11][12][13][14][15][16]. It has been found that deformation of these materials with symmetric fiber stacking configurations can be adequately described in the context of the theory of ort...

We study the elastic deformation behavior of laminated epoxy composites reinforced with unidirectional carbon fibers and satin-woven glass fabric. The efficiency of various experimental procedures of determination of averaged elastic characteristics of laminates is analyzed. The effect of decreasing the test temperature to 77 K on the mechanical behavior of the above-mentioned materials is studied. The possibility of predicting stiffness and compliance parameters of unidirectional or satin-woven fabric composites is discussed. Introduction.Owing to the ever-growing use of composite materials in various modern technological areas, considerable recent attention has been focused on the theories of reinforced materials and advanced processes for producing such materials. Prominent among them are polymeric composites reinforced with high-strength fibers [1]. They offer significant advantages over metals: higher values of specific strength and elastic characteristics, corrosion resistance, lower thermal and electrical conductivities. However, these materials have a low strength and stiffness in compression and shear, their physico-mechanical characteristics are affected by ageing, and the labor input and thus production costs are rather high.During the last decades textile structures have come into use for composite applications. These technologies reduce composite material production costs, allow 3D reinforcement structuring, and ensure a higher product's resistance to mechanical damaging. Furthermore, owing to such reinforcement structures a high interaction between fibers is achieved in the whole volume and the product takes on the form that requires no further surface treatment [2,3]. However, the level of application of textile composites is still to reach that of unidirectional laminates. Among the factors that retard the applications of textile composites are the lack of reliable experimental procedures of determination of material mechanical characteristics, the difficulties associated with mathematical modeling of deformation and strength of textile composite members, and the need for advanced composite production processes.Properties of composite materials depend on the properties of their components, the component ratios, the interactions at matrix-fiber interfaces, and manufacturing processes. Deformation, strength, heat resistance, thermostability, and frost resistance of polymers impose the temperature limits on the composite application. Usually, polymeric materials provides reliable operation in the temperature range between their vitrification point and brittleness temperature. For example, operating temperatures for composites with ÉD-10, ÉD-20 type resins are recommended to be between 393 and 473 K. As far as we know, the potential of using these materials at low temperatures, in particular in cryogenic engineering components, has not been adequately explored and an in-depth study of their mechanical behavior under various thermomechanical loading conditions is needed.