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.     

Creep and long-time strength of unidirectional reinforced plastics in compression

An attempt is made to predict the creep and long-time strength of unidirectional reinforced plastics in compression in the direction of the reinforcement from the properties of the components. The reinforcement is assumed to be elastic, while the resin is described by a Boltzmann-Volterraintegral equation with fractional-exponential Rabotnov kernel. Experimentally obtained creep and long-time strength curves are presented for unidirectional reinforced plastics.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 830–835, September–October, 1970.     

Mechanical properties of a hollow-fiber glass-reinforced plastic

The strength and elastic properties of a hollow-fiber glass-reinforced plastic are investigated together with the effect of temperature, and long-time and cyclic loading on its mechanical characteristics. The instantaneous moduli of elasticity and the creep kernel parameters are obtained on the basis of the creep diagrams.Translated from Mekhanika Polimerov, No. 2, pp. 341–345, March–April, 1971.     

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.     

Performance characteristics of plastic pipes

Within the framework of a review of a number of articles concerned with the performance characteristics of plastic pipes, an analysis of the known methods of determining the creep strength of polyethylene pipes is presented, and the shortcomings of the usual method of testing plastic pipes under constant internal hydrostatic pressure (as applied to polyethylene pipes) are discussed. The possibility of using tensile tests on rod specimens at constant stress to determine the long-time brittle strength of polyethylene pipes is considered.Mekhanika Polimerov, Vol. 1, No. 3, pp. 120–128, 1965     

Creep and long-time strength of tubular specimens of asbopolyethylene

Results are presented of an experimental investigation into the mechanical properties of asbopolyethylene obtained by adding 25 parts by weight of asbestos to pure low-density polyethylene to improve strength and stiffness characteristics. Test data on the creep and static strength of tubular specimens of asbopolyethylene at room temperature in uniaxial tension are given. The long-time strength of asbopolyethylene was determined at 20°, 50°, 80° and 100° C. To estimate the effect of adding asbestos to the polyethylene the mechanical characteristics of pure polyethylene and asbopolyethylene are compared.Mekhanika Polimerov, Vol. 1, No. 5, pp. 51–57, 1965     

Determination of the mechanical characteristics of a glass-reinforced plastic during winding

Problems associated with the determination of the transverse modulus of the material under compression during winding are examined. The rheological characteristics of the material are investigated on the basis of the short-time and long-time creep curves for winding processes conducted at normal and elevated temperatures.Ordzhonikidze Moscow Aviation Institute. Translated from Mekhanika Polimerov, No. 1, pp. 162–164, January–February, 1973.     

Time — Moisture superposition

The results of creep tests on PN-3 polyester resin are given for various values of the temperature and moisture content of the material. It is shown that moisture content and time, like temperature and time, have an interchangeable effect on creep; i.e., in addition to a time-temperature (T-t) there is also a time-moisture (w-t) analogy. The (w-t) analogy can be used to predict the long-time creep from accelerated test data.Institute of Polymer Mechanics, Academy of Sciences of the Latian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 780–786, September–October, 1972.     

Deformation and strength properties of carbon-reinforced plastics in compression

The deformation and strength properties of unidirectionally reinforced carbon plastics have been experimentally investigated for uniaxial compression in the longitudinal and transverse directions and at 45° to the direction of reinforcement in both short-time and long-time tests. On the basis of the deformation properties of the components an attempt is made to describe the creep curve of the plastic in all three loading directions. The Mohr theory is used to predict the compressive strengths in the direction of reinforcement and at right angles to the reinforcement.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 29–35, January–February, 1973.     

Method of testing polymer monofilaments for compressive deformability in the radial direction

A method and an apparatus for testing polymer monofilaments in short-time and long-time compressive creep in the radial direction are proposed. By this means it is possible to test five specimens simultaneously with indenters of selected shape at a constant givenload.I. M. Gubkin Moscow Institute of the Petrochemical and Gas Industry. Translated from Mekhanika Polimerov, No. 6, pp. 1112–1114, November–December, 1971.     

Creep strength of anisotropic plates taking account of transverse shear strains

Cylindrical creep buckling of an orthotropic glass-reinforced plastic plate is investigated with consideration of shear creep in the plane xz. In this case the rheology of buckling is not described by the Kirchhoff-Love model, therefore the investigation is carried out using the modified theory of plates [3]. The long-time and instantaneous critical forces are obtained.Mekhanika Polimerov, Vol. 1, No. 5, pp. 114–117, 1965     

Acoustic creep of glass-fiber-reinforced plastic

A method of investigating acoustic creep of polymer composites developing under the effect of static tensile forces and small amplitudes of dynamic stresses with a frequency of 20 kHz acting coaxially with the static loads is considered. Results of investigating acoustic creep of glass-fabric-reinforced plastic are presented. It is shown that the presence of a high-frequency stress component regularly accelerates relaxation processes and reduces considerably the deformation resistance of the material. Generalized curves simulating the long-time static creep of reinforced plastic are constructed by the method of temperature-time, stress-time, and vibration-time analogies. The results of prediction are compared with the control experiment.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 397–404, May–June, 1973.     

Vibrocreep of polymeric materials

Experimental data on the static and vibrational creep of rigid porous polyurethane are used in an analysis of the time dependence of the vibrocreep coefficient and its dependence on the derivative of the stresses created by the incremental vibrational load and the static stress level. It is shown that at a constant value of the static stresses and the incremental vibrational load the vibrocreep coefficient decreases with time and in long-time vibrocreep tends to unity. As the parameter characterizing the vibrocreep coefficient for a given moment of time it is possible to employ the amplitude of the dynamic stress rate. The dependence proposed for describing the vibrocreep coefficient curves satisfactorily describes the experimental data. It is shown that the value of the vibrocreep coefficient does not depend on the static stress level (up to 0.5 of the short-time strength).For Communication 5, see [9].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 643–647, July–August, 1970.     

Testing methods for predicting the life of polymeric materials

On the assumption that the performance of polymeric materials can be predicted only on the basis of long-time tests under conditions similar to those that obtain in practice, the authors consider creep, stress relaxation, and dynamic measurements at various temperatures and frequencies. Theoretical methods of estimating the life of polymeric materials are investigated with allowance for changes in the physical and chemical structure of the polymer and the nonconstancy of the activation energy of the relaxation processes over a broad temperature interval.Lenin Moscow State Pedagogical Institute, Laboratory of Problems Polymer Physics. Translated from Mekhanika Polimerov, No. 2, pp. 212–220, March–April, 1971.     

Creep and length of life of polycarbonate in aggressive media

Experimental data regarding creep of polycarbonate in air, water, and 10% citric acid are presented. It is shown that there is a correlation between the rate of creep and the length of life of polycarbonate, which enables its long term strength to be predicted.Food Industry Technological Institute, Moscow. D. I. Medeleev Institute of Chemical Technology, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 725–727, July–August, 1972.     

Creep stability of anisotropic shallow spherical shells with account for transverse shear strains

The deformation properties of glass-reinforced plastics are approximated by the relations for a homogeneous anisotropic material, only the shear creep strains being taken into account, since the normal forces, coinciding with the direction of the reinforcement, produce much less creep. Deflections commensurable with the thickness of the shell are considered (geometric nonlinearity), but the strain components are assumed small. The nonlinear relations obtained for this problem have been solved (for a particular case) on a computer. At loads less than the long-time critical value the growth of deflections in time is damped; at large loads the rate of growth of deflections increases.Mekhanika Polimerov, Vol. 2, No. 6, pp. 875–885, 1966     

On the construction of a variant of the theory of fracture

A theory of long-time strength that takes into account the accumulation of damage in the material in different directions is used as a basis for obtaining isochronous fatigue strength curves in stress space for complex states of stress.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 648–653, July–August, 1970.     

Long-time strength of high-elastic polymers

This article examines the question of the inadequacy of the Zhurkov equation for describing the laws of long-time strength of polymers, loading of which is accompanied by the development of high-elastic or induced-elastic deformations. On the basis of general considerations concerning the deformation dependence of the stress concentration coefficient and orientation hardening of polymers, a more general relation between static fatigue life and long-time strength is proposed.Mekhanika Polimerov, Vol. 1, No. 6, pp. 85–91, 1965     

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.     

Limiting states of rigid polyvinyl chloride in creep

Creep tests at constant stresses have been carried out on crystalline polyvinyl chloride (PVC) at 16, 40, and 60° to determine its limiting states (i.e., states defining its creep strength, complete cessation of creep strain, and the boundary of the range of invariance of the mechanical properties), which are shown to be described by exponential functions. An approximate method of determining creep is developed; in this method the creep strength is defined as the stress corresponding to the point of intersection of the limiting equilibrium curves and the stress/time-to-rupture curves.Mekhanika Polimerov, Vol. 1, No. 3, pp. 81–86, 1965