Probability characteristics of the shear modulus of glass-reinforced plastics

The results of tests on wound glass-reinforced plastic specimens based on ÉFB-4 epoxy-phenolic-butyral composition and NS 55/6 glass strand reinforcement with a paraffin finish have been subjected to a statistical analysis with the object of determining the probability characteristics of the shear modulus. The shear modulus is determined for unidirectional structures and structures with reinforcement ratios of 1:1, 1:2, and 3:2. The results of the tests are used to determine the mathematical expectation, variance, and probability density function of the shear modulus.Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 1, pp. 160–162, January–February, 1973.     

Relation between the interlaminar shear modulus and thermal conductivity of oriented glass-reinforced plastics

The relation between the interlaminar shear modulus G of oriented glass-reinforced plastics and their thermal conductivity in a direction orthogonal to the plane of reinforcement is investigated. It is shown that G can be predicted from the measured values of and the bending deformations from and the propagation velocity of ultrasound.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Makhanika Polimerov, No. 6, pp. 985–989, November–December, 1970.     

Resistance of glass-reinforced plastics to long-term shear failure

The time dependencies of the strength of glass-reinforced plastics in shear under steady, continuous and alternating loads are examined. Failure under steady and continuous loading is depicted by means of an exponential model of the build-up of damage.Moscow Aviation Technological Institute. Translated from Mekhanika Polimerov, No. 2, pp. 295–302, March–April, 1970.     

Mechanical characteristics of oriented glass-reinforced plastics in shear

The mechanical characteristics of oriented glass-reinforced plastics stressed in shear are considered. Various methods of determining them are compared. The dispersion of the shear strength is characterized and the possibility of glass-reinforced plastics elements failing as a result of low interlaminar shear strength is discussed.Moscow Aviation Technological Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1008–1013, November–December, 1969.     

Experimental determination of the transverse shear modulus of a wound glass-reinforced plastic in creep

It is proposed to determine the interlayer shear modulus in creep starting from the results of bending tests on simply supported beams with a concentrated load. It is assumed that the increase in deflection with time is caused by interlayer creep. The data of creep tests on wound glass-reinforced plastic beams are presented and used to determine the long-time interlayer shear modulus.Leningrad. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 370–372, March–April, 1969.     

Creep and long-time strength of oriented glass-reinforced plastics in interlaminar shear

The creep and long-time strength in interlaminar shear and the creep in compression in the direction of the reinforcement have been experimentally investigated for certain types of oriented glass-reinforced plastics. The specimens in the interlaminar creep tests took the form of short beams loaded in bending. The experimental creep data for shear and compression are well described by the hereditary theory with a kernel of the Abel type (shear) or in the form of a Rabotnov function (compression). If the stresses are constant in time, good agreement with experiment is also given by Findley's form of the aging theory. A deformation criterion of interlaminar shear strength is also obtained. The experimental curves and values of the creep and long-time strength constants are presented.Translated from Mekhanika Polimerov, No. 6, pp. 1003–1012, November–December, 1971.     

Effect of fiber curvature on the modulus of elasticity for unidirectional glass-reinforced plastics in tension

The effect of curvature of the fibers on the modulus of elasticity of unidirectional glass-reinforced plastics (GRP) in tension has been investigated on the basis of the theory of layered reinforced media with random initial irregularities [1,2]. It is shown experimentally that relatively minor distortion of the fibers during manufacture may result in important changes in the modulus of elasticity. A model is proposed for determining the effect of fiber curvature on Young's modulus; experiments on specimens with a given regular fiber curvature indicate good agreement with the theory. The effect of prestressing the fibers on the modulus of elasticity has been studied using commercial AG-4S material and the optimum prestress has been established.Mekhanika Polimerov, Vol. 3, No. 2, pp. 243–249, 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.     

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     

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.     

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

The stresses that develop in the resin at and near the glass-resin interface during the curing of polyester and epoxy glass-reinforced plastics have been experimentally studied by the photoelastic method. The volume state of stress in three mutually perpendicular directions in various sections and in the danger zones is qualitatively and quantiatively described. It is established that the stresses investigated may be the cause of cracking that reduces the tightness and strength of the glass-reinforced plastic.I. M. Gubkin Moscow Institute of the Petrochemical and Gas Industry. Translated from Mekhanika Polimerov, No. 4, pp. 661–667, July–August, 1973.     

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.     

Fatigue strength of glass-reinforced plastics (GRP) in shear in the plane of reinforcement

The results of an investigation of the fatigue strength of three grades of glass-reinforced plastic are described. It is shown that cyclic loading with gradually increasing stress amplitude can be used to determine the fatigue strength at a given ambient temperature and loading frequency.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 928–931, September–October, 1975.     

Resistance of wound glass-reinforced plastics to failure by unwinding

The debonding of wound glass-reinforced plastics is examined from the statistical standpoint. The statistical stress intensity distribution function characterizing the fracture toughness is obtained. The effect of defect size on the critical nominal stresses is discussed.Moscow Aviation Technological Institute. Translated from Mekhanika Polimerov, No. 5, pp. 881–885, September–October, 1969.     

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.     

Analysis of the tensile deformation of glass-reinforced plastics

The deformation of an orthotropic glass-reinforced plastic is considered with allowance for the failure of the resin in the transverse layers.Ordzhonikidze Moscow Aviation Institute. Translated from Mekhanika Polimerov, No. 1, pp. 144–147, January–February, 1970.