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.     

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.     

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.     

Tensile tests on glass-reinforced plastics

The mechanism of failure of glass-reinforced plastics in short-time tensile tests is considered from the statistical viewpoint. It is thus possible to calculate for various materials the damage suffered by the test piece up to failure. This depends on the dispersion of the static properties but not on the absolute dimensions.Mekhanika Polimerov, Vol. 1, No. 2, pp. 93–103, 1965     

Wear resistance of filled epoxypolyamide composites in aggressive media

The authors investigate the influence of certain aggressive media (toxic chemicals) on the wear resistance of filled epoxypolyamide composites. The presence of toxic chemicals in the zone of friction causes a sharp fall in the wear of the polymers. The maximum wear resistance is displayed by epoxypolyamide composites filled with iron powder, cement, or graphite.     

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     

Effect of aggressive media on the fatigue life of plastics

The dependence of fatigue life on concentration has been obtained for PVC and polystyrene exposed to the action of acetone solutions. As the mechanical stress increases, the role of the aggressivity of the medium diminishes, and its corrosion activitya tends to a minimum (a=1). When a polymer is exposed to the action of a binary liquid, both of whose components are aggressive, a transition region is observed on the log 1/-log C curve. In this region the fracture rate increases sharply.Mekhanika Polimerov, Vol. 4, No. 3, pp. 489–493, 1968     

Bending strength of oriented glass-reinforced plastics

The authors consider the effect of the low shear strength and shear stiffness of oriented glass-reinforced plastics (GRP) on the stress distribution and type of failure in bending. On the basis of relations obtained in [1] it is shown that the effect of shears on the magnitude and law of distribution of the normal and shear stresses is important only for very short beams made of materials with a low shear stiffness. An experimental study of the nature of failure in bending has revealed that the chief cause of extension of the region of shear failure of oriented GRP is the low shear strength of the material, and has made it possible to establish the limits of this region for three typical materials. Anisotropy of the elastic properties has little effect on the type of failure in bending.Mekhanika Polimerov, Vol. 2, No. 4, pp. 535–542, 1966     

Mechanical characteristics of radiation-cured glass-reinforced plastics

Data are presented on the mechanical characteristics of oligoester maleates copolymerized with styrene and the corresponding glass-reinforced plastics crosslinked by the thermochemical and radiation methods. It is established that the radiation-cured glass-reinforced plastics have improved strength and stiffness as compared with similar specimens obtained by thermochemical curing.Institute of Mechanics, Institute of High Molecular Compounds, Institute of Physical Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 4, pp. 704–710, July–August, 1969.     

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.