Determination of the magnitude and distribution of the initial stresses in glass-reinforced plastics

Photoelastic stress analysis is used to demonstrate the effect of coupling agents on the residual microstresses, i.e., the stresses that develop at near the glass-resin interface during the curing of polyester and epoxy glass-reinforced plastics and, as a rule, remain throughout the life of the product. Coupling agents of different chemical composition applied to the surface of the glass fibers have different effects on the components of the state of stress and thus can act as a powerful regulating factor.     

Residual stresses in glass-reinforced plastics parts

The determination of the residual stresses in glass-reinforced plastics elements is considered. It is shown that these stresses reach appreciable values and should be taken into account in strength calculations. Quantitative data are supplied for a series of materials. At normal operating temperatures the residual stresses are stable.Moscow Aviation Technological Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1117–1119, November–December, 1969.     

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     

Structural residual stresses in oriented glass-reinforced plastics

A previously proposed method is used to obtain expressions for calculating the residual stresses as a function of the physicomechanical properties of the polymer matrix and the reinforcement ratio. The calculation results are presented and the corresponding state of stress and strain analyzed. There are considerable deviations (in the magnitude and distribution of the stresses) from models that neglect or only take partly into account the interaction of the fibers.Moscow Ordzhonikidze Aviation Institute. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1051–1058, November–December, 1968.     

Calculation of the residual stresses in wound glass-reinforced plastics

The effect of the winding and polymerization conditions on the residual stress distribution in wound glass-reinforced plastic cylinders is subjected to a numerical analysis. The calculations are based on the method proposed in [1]. The computer data are examined and the theoretical and experimental results compared.Moscow Power Engineering Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1026–1030, November–December, 1970.     

Theory of shrinkage stresses in oriented glass-reinforced plastics

The problem of shrinkage stress distribution in glass-reinforced plastics is examined on the basis of an improved model under certain assumptions concerning the nature of the curing process. Cylindrical tubes of epoxy glass-reinforced plastic are investigated under stepped temperature conditions.Mekhanika Polimerov, Vol. 1, No. 6, pp. 61–68, 1965     

Fiber distribution in oriented glass-reinforced plastics

The distribution of the fibers in the structure of a glass-reinforced plastic has been experimentally investigated. Data have been obtained on the distribution of interfiber distances, fiber diameters, and the angles between the lines of centers. Experimental histograms and distribution curves are constructed.Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 282–287, March–April, 1969.     

Experimental determination of residual stresses in wound unidirectional glass-reinforced plastics

The residual stresses in prestressed ring-shaped systems of wound unidirectional glass-reinforced tape have been investigated experimentally. The relation between the residual stress and the winding force has been established. A decrease in the specified prestress is demonstrated. The results of tensile tests on free rings of wound glass-reinforced tape are presented.Mekhanika Polimerov, Vol. 2, No. 1, pp. 123–129, 1966     

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.     

Results of an experimental investigation of the residual stresses in wound glass-reinforced plastics

The results of an experimental investigation of the residual stresses in wound glass-reinforced plastic rings are presented. The residual stresses were determined by the Davidenkov method. The dependence of the maximum tensile and compressive circumferential stresses on ring thickness and polymerization temperature is investigated. The experimental data are compared with the results of calculations based on the theory proposed in [1, 2].Moscow Power Engineering Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1116–1119, November–December, 1970.     

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     

Determination of the residual stresses in wound glass-reinforced plastic rings

The stresses that develop during winding in wound glass-reinforced plastic rings change during polymerization, when the modulus of elasticity in the radial direction is reduced by heating. Further changes occur in connection with cooling and removal from the mandrel. The theoretical relations obtained for determining these stresses are found to be confirmed by experiment.Bauman Moscow Higher Technical College. Translated from Mekhanika Polimerov, No. 5, pp. 892–898, September–October, 1969.     

Statistical strength of glass-reinforced plastics

The failure of glass-reinforced plastics is treated as an aggregate of successive failures of the individual fibers. A method of estimating the statistical strength from the distribution curve is proposed.Mekhanika Polimerov, Vol. 3, No. 3, pp. 498–502, 1967     

Programmed winding of glass-reinforced plastics

It is proposed to employ a variable winding tension designed to give a required initial stress distribution. The program is constructed on the basis of solutions describing the loss of tension associated with winding and the softening of the resin during heat treatment. The problems are solved in the elastic formulation. Programs are obtained for three cases: constant tension in a ring sill on the mandrel, compensation of the stresses that develop after removal from the mandrel, and compensation of the thermoelastic stresses that develop during cooling.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 48–53, January–February, 1970.     

Static fatigue of glass-reinforced plastics

Nonlinear damage accumulation rules are usually constructed on the basis of certain hypotheses derived from semiempirical considerations. A method is proposed for constructing an averaged nonlinear damage accumulation rule based on the direct utilization of the results of static fatigue tests on glass-reinforced plastic specimens. Numerical examples of the calculation of the static fatigue strength under repeat loading with a given strength criterion are presented.Sverdlovsk Branch of the Steklov Mathematical Institute, Academy of Sciences of the USSR. Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 492–497, May–June, 1969.     

Relaxation characteristics of glass-reinforced plastics

A study was made of the relaxation properties of glass-reinforced plastics KAST-V, ÉDF, SVAM, and Textolite. The article gives experimental and theoretical values of the pliabilities and tables of the values of the relaxation properties required for the solution of boundary value problems in viscoelasticity.M. V. Lomonosov State University, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 560–562, May–June, 1970.     

Residual stresses in glass-reinforced polyethylene

The variation of the axial and radial components of the residual stresses in fiber-reinforced polyethylene with distance from the fiber has been investigated. It is shown that, irrespective of the agent employed, coupling leads to an increase in stresses. The values obtained for the residual stresses are compared with the adhesion strength determined by the shearing method. The effect of a structure-forming agent on the residual stresses is investigated.Mendeleev Moscow Chemical Engineering Institute. Translated from Mekhanika Polimerov, No. 4, pp. 722–724, July–August, 1971.     

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.