Influence of vibration on creep in glass-fiber-reinforced plastic in a complex state of stress

The author describes the method and results of tests on tubular specimens of glass-fiber-reinforced plastic for creep under simultaneous torsion (shear in the plane of reinforcement), compression, and vibration in the longitudinal direction. He finds that vibratory creep is not manifested if the amplitudes of the alternating component of the stress are up to 0.1 times the limit of short-term strength and the frequency is 20 kHz.Institute of Mechanics of Polymers, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 358–360, March–April, 1974.     

Strengthening of glass-fiber-reinforced plastic under biaxial tension

Conclusions 1. The effect of axial tension, applied at the first stage of loading under biaxial tension, on the increase in the hoop strength of an oriented glass-fiber-reinforced plastic was observed. The increase in the hoop strength depends both on the value of the axial tensile load, and on the angle of winding of the fibers.2. The effect observed is in this case apparently independent of the condition of loading of the sample under biaxial tension.Institute of Mechanics, Academy of Sciences of the Armenian SSR, Erevan. Translated from Mekhanika Polimerov, No. 6, pp. 1025–1029, November–December, 1976.     

Fatigue of a glass-fiber-reinforced plastic under sonic-frequency vibrations

A procedure is described for fatigue tests of glass-fiber-reinforced plastics specimens under conditions of symmetrical extension and compression with a steady peak of dynamic stress at a vibration frequency of approximately 500 Hz. As a test for fatigue failure we chose the steep increase in the mechanical loss angle of the vibrating system which occurs when a macrocrack is formed in the specimen. The time dependence has been plotted for the mechanical loss angle, the resonance frequency of the vibrations system, a parameter proportional to the peak deformation of the specimen, and the temperature of vibrational heating-up in its cross section where there is the greatest stress. The progress of these dependences has been analyzed in the build-up of fatigue damage in the material. An experimental relation has been obtained between the resultant dissipative function of the material and the peak dynamic stress. Results are given of fatigue tests on specimens of a glass-reinforced plastic winding cut in the weft direction of the reinforcing fabric.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1039–1043, November–December, 1972.     

Statistical analysis of some characteristics of cylindrical glass-fiber-reinforced plastic materials

The results are given of a statistical treatment of experimental data on several characteristics of glass-fiber-reinforced plastic cylindrical shells, prepared from glass fabric TS8/3-250 and epoxide binder IF-ÉD-6 (TU-26-59) at the "Électroizolit" factory by winding an impregnated fabric cloth on a mandrel. The experim ental data on the mechanical properties of the glass-fiber-reinforced plastic material were obtained in tests on representative samples cut from the margin of the cylindrical shells. The results of the statistical analysis can be used to evaluate the mechanical reliability of structures made of glass-fiber-reinforced plastic material of the above type.Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 906–910, September–October, 1973.     

Reaction of sloping spherical shells of glass-fiber-reinforced plastic during nonstationary loading

The behavior of spherical shells of glass-fiber-reinforced plastic under the action of exponentially changing dynamic loading was studied in a nonlinear formulation. The method of finite differences, used in the form of an explicit difference scheme, was used to solve the differential equations of the dynamics of sloping shells based on the Kirchhoff-Love hypotheses. The characteristic features of the deformation process and the influence of the degree of anistropy of the shell material operating under conditions of dynamic loading are noted.Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 311–314, March–April, 1975.     

Transient creep of glass-reinforced plastic

Short-time (up to 30 min) creep tests on SVAM glass-fiber orthotropic material at 20°C have shown that it is subject to creep even at room temperature. At the same time, the behavior of this material in creep is observed to be markedly anisotropic.Mekhanika Polimerov, Vol. 1, No. 2, pp. 47–54, 1965     

Plane-stress creep of a glass-reinforced plastic

The creep behavior of an orthotropic glass-reinforced plastic based on Polimal'-109 resin and 19-S4 glass fabric is described. A special device for testing tubular specimens in plane-stress creep has been designed. The loading conditions include combined torsion and tension, internal pressure, and loading along the principal directions of anisotropy. Constitutive equations describing creep and recovery are proposed for the two-dimensional case.Warsaw. Translated from Mekhanika Polimerov, No. 3, pp. 398–410, May–June, 1971.     

A method of preventing cracking during heat treatment of thick-walled glass-fiber-reinforced plastic shells

To avoid cracking of thick-walled glass-fiber-reinforced plastic shells during heat treatment, it is suggested that the shells should be heat treated under pressure. This method is based on a comparison between the kinetics of the internal stresses σ_r.max(T) and strength σ _r ^str (T) during cooling. The authors give expressions for the optimum pressure, based on an elastic model of the material.     

Compensation of thermal stresses in glass-fiber-reinforced plastic articles by the layerwise winding method

The contact pressures which must be created during winding with layerwise hardening in order to compensate radial stresses on the contact surfaces of the layers are determined. The tensions realizing the necessary pressures are calculated. The relations obtained are checked experimentally.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 640–645, July–August, 1972.     

Load-bearing capacity of compressible plates of glass-fiber-reinforced plastic with different placement of the reinforcement

The effect of placement of reinforcement on the load-bearing capacity of circular and rectangular plates compressible in the reinforcement plane was evaluated experimentally. Four placement schemes for circular plates and nine for rectangular plates were investigated. Different schemes of supporting the edges were studied. Two mechanisms of exhaustion of the bearing capacity were revealed. A numerical evaluation and comparison of different placement schemes with respect to the value of the critical and breaking load are given. The role of the actual realization of clamping and nonlinearity of the material is shown. A comparison with analytic relations taking into account the characteristics of the material is given.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 646–653, July–August, 1972.     

Modeling the creep stability of plastic shells

The problem of modeling the creep stability of shells is investigated on the basis of the strain compatibility, equilibrium and physical equations, and the boundary conditions. The mechanical similarity of physically nonlinear elastic and elasto-hereditary materials is examined in detail. The concept of an elastic potential and Volterra-type integral relations with increasing multiplicity are employed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1059–1063, November–December, 1969.     

Some creep properties of AG-4V glass-reinforced plastic

Creep test results for AG-4V glass-reinforced plastic in compression are presented for the temperature range 20–150° C. Some qualitative and quantitative characteristics of the dependence of strain on temperature, stress, and orientation are noted.Mekhanika Polimerov, Vol. 1, No. 5, pp. 30–33, 1965     

Effect of “rest” on creep of glass-reinforced plastic SVAM

The effect of rest on creep of glass-reinforced plastic SVAM is investigated. It is shown that for the cyclic loading regime used (24-h load, 24-h rest) the effect of rest is closely related with orientation of the specimen and with the magnitude of the load.Institute of Mechanics, Academy of Sciences of the Armenian SSR, Erevan. Translated from Mekhanika Polymerov, No. 3, pp. 547–550, May–June, 1974.     

Nonlinear creep of TS8/3-250 glass-reinforced plastic

The creep and recovery of a glass-reinforced plastic are investigated within the frame-work of a nonlinear hereditary model. The material characteristics are determined for the three principal directions. The proportionality of the kernels is established.State Scientific-Research Institute of Machine Science, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 391–397, May–June, 1971.