Statistical theory of elasticity of reinforced plastics

A method of solving statistical boundary value problems in the stresses is proposed for microinhomogeneous composite media simulating the structure and properties of reinforced plastics. The coefficients of variation of the physical properties of the medium are not assumed small. Numerical examples are presented.Mekhanika Polimerov, Vol. 4, No. 3, pp. 438–444, 1968Presented on 5 June 1967 at a scientific seminar held at the Institute of Polymer Mechanics of the Academy of Sciences of the Latvian SSR.     

Structural theory of the strength of reinforced plastics

Conclusions In the present study, we developed structural criteria that make it possible to predict at the component level (polymer binder, fibers) and interface level the long-term strength of laminated reinforced plastics in a plane stress state. The proposed relations make it possible to evaluate the effect of the rheological properties of the components, their volume fractions, and the geometry of the structure of the laminated packet on the long-term strength of reinforced plastics. The relations also permit resolution of the inverse problem: efficiently design the structure of such materials for specific loading conditions.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 833–839, September–October, 1989.     

Fundamentals of the theory of non-fabric glass-reinforced plastics

Starting from the known mechanical properties of the components (glass reinforcement and resin) the stress-strain relations for an anisotropic viscoelastic material (glass-reinforced plastic) are determined. Using Volterra's principle [2] of replacing the elastic constants in the solution of the problem of the theory of elasticity [5] by integral operators, relations for the given material are obtained and found to be in fairly good agreement with the experimental data. In a separate study the high-temperature behavior of GRP is investigated by calculating the integral operators, which are functions of the viscous properties of the resin and the temperature.Mekhanika polimerov, Vol. 1, No. 1, pp. 151–158, 1965     

On the theory of anisotropic creep of unidirectional glass-reinforced plastics

The basic relations of the theory of anisotropic creep of unidirectional glass-reinforced plastics (GRPs) in a three-dimensional stress state are found using a model of a material with inhomogeneous structure and the rheological properties of the resin. These relations are suitable for investigating the stress state of GRPs for resin stresses not exceeding certain values. The phenomena of simple creep and stress relaxation are studied with reference to a unidirectional GRP with an epoxy-maleic resin matrix.Mekhanika Polimerov, Vol. 1, No. 2, pp. 64–69, 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.     

Statistical theory of elasticity of reinforced plastics with internal stresses of shrinkage origin

The statistical boundary value problem of the theory of elasticity of macrohomogeneous composite media in the natural (unstressed) starting state is extended to media with internal stresses of shrinkage origin. It is established that the moduli of elasticity of the composite do not depend on the magnitude of the shrinkage stresses. The conditions, under which shrinkage of the resin in materials of the glass-reinforced plastic type does not lead to warping, are determined. Applications of the results to the computation of structural reliability characteristics are noted.Kirov Ural Polytechnical Institute, Sverdlovsk. Translated from Mekhanika Polimerov, No. 4, pp. 676–681, July–August, 1970.     

Basic relations of the theory of oriented glass-reinforced plastics (GRP) with hollow fibers

A method has been developed for theoretically determining the physico-mechanical properties of glass-reinforced plastics (GRP) with hollow fibers. Approximate formulas for the rapid determination of the principal mechanical characteristics are derived.Mekhanika Polimerov, Vol. 2, No. 5, pp. 763–772, 1966     

Determination of residual stresses in plastics

A method is proposed for calculating the residual stresses in hot-molded plastics parts. Data are presented for a polyester glass-reinforced plastic.Mekhanika Polimerov, Vol. 3, No. 5, pp. 827–832, 1967     

Structural stresses in reinforced plastics

The safety parameters at any given point of a microinhomogeneous medium simulating the structure and properties of reinforced plastics are determined by solving the statistical boundary value problem. The results are illustrated in relation to randomly reinforced glass laminates.Mekhanika Polimerov, Vol. 3, No. 3, pp. 413–420, 1967     

Glass-reinforced plastics based on matrices combining thermoplastics and thermosetting plastics

The conditions of fabrication and the physicomechanical properties of glass-reinforced plastics based on polysulfone combined in different ratios with epoxy resin and Rolivsan were investigated. It was found that realization of the strength of the fibers in glass-reinforced plastics based on three types of binders and mixtures of them at room temperature is approximately the same. The lower strength of glass-reinforced plastics based on polysulfone is determined by the lower concentration of fibers. Modification of thermosetting plastics with polysulfone significantly increases (by 5–8 times) the specific energy of delamination of the glass-reinforced plastics G_1c, which should be manifested by an increase in their crack resistance and other operating characteristics. Modification of ED-20 with polysulfone and polysulfone with Rolivsan significantly increases the glass transition temperature of the polymer and affects the character of the temperature curves of the strength of the glass-reinforced plastics.Institute of Chemical Physics, Russian Academy of Sciences, Moscow. D. I. Mendeleev Russian Chemical Technological University, Moscow. Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 111–117, January–February, 1996.     

Theory of thermostructural stresses in reinforced plastics

A method is proposed for determining the mean values of the initial thermostructural stresses in reinforcement and matrix resulting from the uniform cooling of a two-component unloaded elastic body from the natural state (resin hardening temeprature) to the working temperature (external loading).V. A. Steklov Mathematical Institute, Sverdlovsk Branch, Academy of Sciences of the USSR. S. M. Kirov Ural Polytechnic Institute, Sverdlovsk. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 822–828, September–October, 1968.     

Deformation characteristics of glass-reinforced plastics in tension

It has been shown experimentally with reference to two glass-reinforced plastics (reinforced with fabric and rovings) that at stresses above the break on the stress-strain curves the ratio of the transverse strains ₃ developing at right angles to the layers and the longitudinal strains ₁ changes. Raising the test temperature of the glass laminate intensifies this change.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 373–375, March–April, 1969.     

Variation of prestress in filament-wound glass-reinforced plastics

The authors examine the process of winding prestressed parts from oriented glass-reinforced plastics. It is shown that the essential anisotropy of the properties of these materials in responsible for variation of the specified prestress. The law of distribution of the tensile forces is investigated in the linear-elastic approximation for the case of a ring wound onto a rigid mandrel. A method of calculation is proposed that permits the change in prestress to be estimated and gives the critical number of turns beyond which the pressure on the mandrel ceases to increase.Mekhanika Polimerov, Vol. 2, No. 2, pp. 278–284, 1966     

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     

Wear of glass-reinforced plastics in aggressive media

The effect of certain aggressive media on the wear of glass-reinforced plastics has been investigated. It is shown that as the angle of inclination of the glass reinforcing fibers relative to the friction surface increases, the wear of the material is sharply reduced.Ukrainian Agricultural Academy, Kiev. Translated from Mekhanika Polimerov, No. 2, pp. 364–366, March–April, 1974.