Creep and long-time strength of unidirectional reinforced plastics in compression

An attempt is made to predict the creep and long-time strength of unidirectional reinforced plastics in compression in the direction of the reinforcement from the properties of the components. The reinforcement is assumed to be elastic, while the resin is described by a Boltzmann-Volterraintegral equation with fractional-exponential Rabotnov kernel. Experimentally obtained creep and long-time strength curves are presented for unidirectional reinforced plastics.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 830–835, September–October, 1970.     

Investigation of internal stresses in glass-reinforced plastics

The strength properties of and internal stresses in epoxy and epoxyphenol resins and GRPs based on them are investigated using an optical method of determining internal stresses. The GRPs had tape and fabric reinforcement. Compared with the internal stresses in unplasticized specimens, the stresses in pure resin films and in GRPs based on plasticized resins are found to be smaller. It is shown that the distribution of internal stresses in GRPs is anisotropic. The highest internal stresses are observed in tape-reinforced GRPs in a direction normal to the fibers. Glass reinforcement in two directions at right angles reduces the internal stresses in GRPs as compared with pure resin films. In both reinforced and unreinforced films, the internal stresses depend on the curing conditions.Mekhanika polimerov, Vol. 1, No. 1, pp. 82–88, 1965     

Tensile strength of unidirectionally reinforced plates stretched at an angle to the direction of reinforcement

Conditions for the fracture of a unidirectionally reinforced plate under uniaxial tension at an arbitrary angle to the direction of reinforcement are proposed. The fracture conditions are applicable to the case where the adhesion strength between the bond and reinforcement is greater than the strength of the polymer bond. The strength of the polymer bond in the volume stressed state is determined by an energy criterion.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 482–486 May–June, 1973.     

Strength and deformability of reinforced polymers in tension normal to the fibers

The strength and deformability of reinforced polymers in tension across the fibers is investigated. It is assumed that the polymer deforms as an ideal elastoplastic body. Relations are obtained for the nature of the deformation of the polymer between the fibers and the strength and deformability of the composite with allowance for the structural distribution of the components. Theoretical stress-strain diagrams are presented for composites with different reinforcement densities and resin elasticities. The theoretical values of the strength and deformation of reinforced polymers with the load applied across the fibers are compared with the results of experiments on model specimens of epoxy-Thiokol polymers.Leningrad Mechanical Institute. Translated from Mekhanika Polimerov, No. 4, pp. 682–687, July–August, 1970.     

Continuity condition for orthogonally reinforced plastics in tension

The proposed continuity condition is based on the hypothesis that the time dependence of the strength and limiting strain of the resin is determined by the limiting value of the specific work done by the stresses. The case when the reinforcement is elastic and the rheological properties of the resin are described by a linear differential equation is considered.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 844–852, September–October, 1968.     

Creep of reinforced plastics in uniaxial tension along the fibers

Relations are proposed for determining at any moment of time the strains in a reinforced plastic stressed in the resin and the reinforcement by a constant tensile load as a function of the reinforcement ratio and the rheological properties of the reinforcement and resin. The proposed relations agree quite well with the experimental data.Mekhanika Polimerov, Vol. 1, No. 6, pp. 69–77, 1965     

Structural theory of the tensile and compressive strengths of reinforced plastics

The strength conditions of unidirectionally and orthogonally reinforced plastics subjected to uniaxial tension and compression in the direction of, and at an angle to, the reinforcement are developed, with consideration given to possible failure of the fibers, binder, or the bond between the fibers and binder. Proposed strength conditions take into account the structure of the material, the properties of its components, and stress concentration.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 988–995, November–December, 1975.     

Effect of fillers on the structure and properties of cured resins

It is shown for the first time that the increased strength of filled plastics is associated with an increase of the internal pressure in the resin determined by the nature of the filler surface and the curing conditions.For communication 1, see [1].Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 54–58, January–February, 1970.     

Study of the residual (internal) stresses in reinforced epoxy resin

An optical polarization method has been used to study the residual (internal) stresses in reinforced ED-6 epoxy resin cured with maleic anhydride. The effects of "chemical" shrinkage, volume change relaxation during during curing, and the difference linear coefficients of thermal expansion for reinforcement and resin are elucidated. It is shown that adjacent reinforcing elements interact. The stress state is investigated with reference to a model of the elementary cell of the regular structure of a unidirectional glass-reinforced plastic. The residual stresses are found as a function of the resin/reinforcement ratio.Mekhanika Polimerov, Vol. 1, No. 4, pp. 76–80, 1965     

Possibilities of a nondestructive one-parameter method of checking the strength of anisotropic glass-reinforced plastics in uniaxial compression

A nondestructive method of checking the strength of glass-reinforced plastics (GRP) in finished products is proposed. This method is based on the correlation, investigated by the authors, between the modulus of elasticity and the compressive strength determined by a standard method. Various orientations in the plane of reinforcement of glass-reinforced plastics with different ratios of the orthogonally arranged fibers are investigated. It is proposed to determine the modulus of elasticity from the propagation velocity of an ultrasonic pulse measured under conditions of one-sided access to the surface of the product."Ritm" Research-Production Association, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 909–919, September–October, 1974.     

Mechanism of failure of reinforced beams in bending

The mechanism of shear failure is investigated. A theoretical analysis makes it possible to determine the limits of shear failure of reinforced beams in relation to the geometric parameters of the beam, the mechanical properties of the reinforcement and the resin, their volume content, and the loading and support conditions. The results obtained are consistent with the experimental data of [1]. It is shown that in the process of shear failure the axial displacement distribution is modified and that the shear failure mechanism depends on the type of loading and the support conditions.Institute of Hydrodynamics, Siberian Branch, Academy of Sciences of the USSR, Novosibirsk. Translated from Mekahnika Polimerov, No. 4, pp. 698–709, July–August, 1973.     

Tensile testing of high-strength unidirectional composites

Conclusions 1. In order to obtain stable values of the tensile strength of high-strength unidirectional composites it is necessary to use bar specimens with pressboard end reinforcement 90–110 mm in length.2. In determining the strength on specimens without end reinforcement it is necessary to select their size and shape with allowance for the transverse compressive strength, the shear strength and the taper of the grip jaws.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 717–723, July–August, 1978.     

Effectiveness of using hollow fibers to improve the rigidity of glass-reinforced plastics

Calculated and experimental relations between the modulus of elasticity and rigidity of unidirectional glass-reinforced plastics (GRP) and the capillarity coefficient of the hollow fiber reinforcement are presented. It is established that in calculating the flexural rigidity ratio of hollow- and solid-fiber GRP specimens of equal weight it is not permissible to neglect the mass and modulus of elasticity of the resin. The potentialities of hollow fibers as reinforcement for GRP shells subjected to external pressure are demonstrated.All-Union Scientific-Research Institute of Glass-Reinforced Plastics and Glass Fibers, Moscow Region. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 672–676, July–August, 1968.     

Optimal reinforcement of a material in a known state of stress

The problem of minimizing the total reinforcement of a material in a known state of stress is considered. In the proposed geometric formulation the problem reduces to the determination in normal stress space of the shortest path from a point representing the state of stress to the region of strength. Examples of the determination of the relative area of reinforcement in three-dimensional and plane states of stress are given for characteristic regions of strength: for plane stress and plane strain the calculations lead to expressions that permit the relative areas of reinforcement to be determined directly.Kucherenko Central Scientific-Research Institute of Building Structures, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 922–930, September–October, 1971.     

Effect of elevated temperatures on the strength of cured resins and resin-based materials

An analysis of the relationship between the relative changes of compressive strength and weight loss for glass laminates has shown that at elevated temperatures (to 600° C) the changes in strength are primarily caused by processes of mechanical destruction of the resin phase. The process of thermo-oxidative degradation of the resin in the laminate is described by the same stages as were detected in studying cured resins.Moscow Aviation-Engineering Institute. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 832–838, September–October, 1968.     

Dependence of elastic and strength characteristics of high-modulus composites on schemes of reinforcement

The elastic and strength characteristics of high-modulus composites with 12 different reinforcement schemes have been studied thoroughly. The effect of reinforcement schemes on change in elastic and strength characteristics of composites has been evaluated. A calculation of the elastic characteristics of high-modulus composites has been performed from the properties of the reinforcement and binder, and a comparison of the results with experimental data is given. Diagrams of deformation upon extension of the composites studied are given.All-Union Scientific-Research Institute of Aviation Materials, Moscow. Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1019–1027, November–December, 1974.     

Investigation of the anisotropy of the properties of glass-reinforced plastic shells

The load-carrying capacity and deformation of cylindrical and conical glass-reinforced plastic (ÉDT-10 resin) shells loaded in axial compression have been investigated experimentally in relation to the orientation of the fabric reinforcement. The results of the tests are compared with the relations of the theory of elasticity of an orthotropic body.Zhukovskii Central Aerohydrodynamics Institute, Moscow Region; Scientific Research Institute of Production Technology and Organization, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 814–818, September–October, 1969.     

Critical compressive stresses in cylindrical shells composed of orthotropic layers with different orientations

The laws of variation of the strains and critical stresses for smooth thin circular cylindrical glass-reinforced plastic shells based on ÉDT-10P resin have been experimentally investigated at different orientations of the fabric reinforcement. The results of the tests are compared with the theoretical data obtained from the relations of the theory of elasticity of an orthotropic body and orthotropic shells.N. E. Zhukovskii Central Aerohydrodynamic Institute of Production Technology and Organization, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 684–690, July–August, 1973.     

Deformation and strength properties of carbon-reinforced plastics in compression

The deformation and strength properties of unidirectionally reinforced carbon plastics have been experimentally investigated for uniaxial compression in the longitudinal and transverse directions and at 45° to the direction of reinforcement in both short-time and long-time tests. On the basis of the deformation properties of the components an attempt is made to describe the creep curve of the plastic in all three loading directions. The Mohr theory is used to predict the compressive strengths in the direction of reinforcement and at right angles to the reinforcement.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 29–35, January–February, 1973.     

Effect of a filler on the strength properties of thermosets

The effect of a filler on the strength properties of polymers in tension is investigated. The thermostructural stresses that develop in the composite during cure are taken into account. Relations are given for the strength of the filled polymer as a function of the percentage filler content. In the process of analyzing the thermostructural stresses an analytic expression is obtained for the linear expansion coefficient of the composite with allowance for the structural distribution of the components. Calculated values of the strength and thermostructural stresses are presented for composites with different filler contents. The theoretical determination of the strength of filled polymers is compared with the results of experimental investigations of composites based on epoxy resin filled with quartz dust.Leningrad Mechanical Institute. Translated from Mekhanika Polimerov, No. 1, pp. 97–101, January–February, 1973.