Analitical Description of the Creep of Expanded Polystyrene under Compressive Loading

Data obtained in testing the creep of expanded polystyrene plates in compression are discussed. Power-type and exponential regression equations are used for describing the compression creep curves. Within the limits of data spread, both these equations represent experimental results equally well. A correlation between the creep strain and density, the compressive stress at a 10% strain, and the elastic modulus in compression is revealed for the material investigated.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 4, pp. 525–534, July–August, 2005     

Creep of polymer materials under periodically varying loads

A method is proposed for constructing the creep curves of a material whose nonlinear memory properties are described by Rozovskii's nonlinear integral equation [2] (with allowance for the stress dependence of the relaxation time) under given periodic loading from known creep curves recorded at constant stress. In deriving the theoretical relation certain simplifying assumptions are made (the creep strain accumulated in 1–2 cycles is small, no vibration [4–6]). An experimental check shows that the proposed method can be used to predict the behavior of a material under periodic loading with an accuracy sufficient for practical purposes.Mekhanika Polimerov, Vol. 2, No. 3, pp. 330–336, 1966     

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.     

Structural diagram of furfural-acetone plastic concrete in compression

The attenuation of plastic concrete creep is analyzed on the basis of the structural diagram, and a formula relating total strain and compressive stress is derived. This formula is in good agreement with the experimental data, as demonstrated by fitting the experimental creep curves.Mekhanika Polimerov, Vol. 4, No. 3, pp. 454–461, 1968     

Investigation of the one-dimensional problem of nonlinear creep

A method of analyzing experimental creep curves of a nonlinear viscoelastic material to obtain relaxation curves is examined. It is assumed that the family of creep curves in question cannot be represented as a product of the stress function and a function of time. The investigation is carried out using the memory theory. The sum of the exponentials for curves not having a singularity at the start of the process is taken as the creep kernel [1]. A method of approximation by the sum of the exponentials is given. For processes with an initial singularity it is proposed to use the corresponding kernel, for which the resolvent is given.Mekhanika Polimerov, Vol. 2, No. 5, pp. 678–687, 1966     

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.     

Choice of kernels in solving problems involving creep and relaxation

For the memory theory analysis of creep and relaxation processes whose rates have a singularity at the beginning of the process it is proposed to employ a kernel and the corresponding resolvent in the form of a series whose convergence is proved. An estimate of the convergence and an asymptotic formula for large times are also presented. The kernel, the resolvent and their integrals have been tabulated. Theoretical curves are constructed for certain parameters, and it is shown how they can be used in analyzing creep problems when the object is to find relaxation (creep) curves from experimental creep (relaxation) curves. It is noted that, given a suitable choice of parameters, it is possible to use the proposed functions to describe both finite and unlimited creep.Mekhanika Polimerov, Vol. 2, No. 4, pp. 483–497, 1966     

Determination of regular discrete relaxation spectra from the viscoelastic functions

A procedure for determining regular discrete relaxation spectra from the viscoelastic functions is presented as a generalization of a previously proposed procedure for determining the conditional rheological characteristics in a piecewise-exponential approximation of the experimental creep, relaxation, and – curves. The calculated data are in good agreement with the experimental results.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 801–807, September–October, 1971.     

Analysis of nonlinear polymer creep

The relaxation properties of polyethylene are analyzed. The nonlinear time-dependent stress-strain relations and the creep and relaxation equations are obtained from the experimental creep data. The analysis is based on an appropriate variant of the nonlinear memory theory with singular functions whose parameters, together with the modulus of elasticity, are determined by the method described in [1].Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 410–414, May–June, 1969.     

Investigation of the integral creep equations (cubic nonlinearity) for different loading paths

Expressions for the creep strain obtained in accordance with the Leaderman-Rozovskii theory and in the form of a multiple-integral Volterra series are compared for different loading paths. The influence functions are assumed to be symmetrical. The strain intensity-time curves are calculated for a complex loading path for which the stress intensity is constant. It is found that these curves are nonmonotonic for both linear and nonlinear creep.Read at Fourth Symposium on Rheology, Moscow, May 27–30, 1969.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 35–42, January–February, 1970.     

Creep of unidirectional glass-reinforced plastics based on new types of fibers

Theoretical and experimental compressive creep relations for a unidirectional glass-reinforced plastic based on hollow fibers are presented. The agreement between the theoretical and experimental data is shown to be satisfactory. The effect of fiber capillarity on the creep process is unimportant.All-Union Scientific-Research Institute of Glass-Reinforced Plastics and Fiber Glass, Moscow; Institute of Mechanics of Machines and Polymeric Materials, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Mekhanika Polimerov, No. 4, pp. 747–750, July–August, 1971.     

Applicability of influence functions determined from quasi-static experiments for solving dynamic problems of vibration protection

Creep of shock-absorbing foamed materials and a vibration-protecting structure is investigated. The parameters of the influence functions, whose numerical realization is conducted in solving the dynamic problem of vibration protection, are determined from the creep curves by the method of logarithmic matches. The conclusions agree with the experimental.Moscow Institute of Electronic Machinery. Translated from Mekhanika Polimerov, No. 3, pp. 537–540, May–June, 1975.     

Photoelastic determination of polymer creep stresses and strains

A physical basis provided for the relation between the measured optical quantities and the unknown mechanical quantities in the photoelastic determination of stresses and strains. Questions relating to the "freezing in" of strains are considered in connection with creep tests on models made of optically sensitive polymeric materials. The determination of the stress concentration at the edge of an opening in a strip tested in creep is considered as an example of the application of the theory.Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 739–746, July–August, 1970.     

Influence of physical aging on creep of rubber

The effect of physical aging on the creep response of chloropren rubber filled with carbon black was studied. The method of reduced variables and analytical method of determination of influence of physical aging on the creep compliance in short creep time test are proposed.Glówny Instytut Górnictwa, Pl. Gwarków 1, 40–166 Katowice, Poland. Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 112–118, January–February, 1997.     

Nonlinear creep of a glass fabric-reinforced plastic in several complex states of stress

Tensile, compressive, torsional, and combined creep tests have been performed on tubular specimens of a glass fabric-reinforced plastic. The sign of the normal stress has been found to have an important influence on the development of the shear creep strains. The rheological parameters of the material necessary for approximating the test curves have been determined and the results of the calculations compared with experiment.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 212–218, March–April, 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.     

Creep of polyester resin PN-3 under moisture-absorption conditions

A procedure is described for testing samples for creep in a climatic chamber of the Feutron 3001 type. Results of an experimental study of forward and back creep of polyester resin PN-3 under simultaneous moistening of samples in an air medium with elevated humidity are discussed. It is shown that the rate of the creep process depends greatly on the humidity state of the material.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 579–584, July–August, 1972.     

Lifetime analysis with allowance for bond stress distribution

A fracture model consisting of a set of bonds assigned various stress concentration coefficients is proposed. The bond lifetime is determined from Zhurkov's equation; the relative number of bonds with a particular _* being taken in accordance with a Weibull distribution. The model explains the similarity of the shapes of the submicrocrack accumulation and creep curves.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 227–231, March–April, 1973.     

Determination of coupled creep functions from experimental creep curves

A method is given for constructing the coupled creep functions g(t) from the experimental longitudinal creep curves and the known Poisson's ratio. It is shown that for this purpose it is sufficient to substitute for one of the parameters of the singular kernel a quantity containing the Poisson's ratio and the parameter determined from the solution of the elastic problem.I. M. Gubkin Moscow Institute of the Petrochemical and Gas Industry. Translated from Mekhanika Polimerov, No. 2, pp. 216–220, March–April, 1974.     

Determination of the rheological characteristics of polymer materials from the static σ-ε curves and creep and relaxation curves

A method is proposed for determining the rheological characteristics of polymer materials from the experimental - curves and the creep and relaxation curves, when the behavior of the material is described exactly and approximately by the equation of a standard solid, together with a method of determining the conditional rheological characteristics when only a certain section of these curves is approximately described by the equation of a standard solid. The proposed method makes it possible to eliminate the ambiguity in the determination of the rheological characteristics due to difficulties in the exact determination of the coordinates of the beginning and end of the static curves. The use of conditional rheological characteristics makes it possible to describe the behavior of polymer materials over a broad time interval under static loading conditions by means of the equation of a standard solid without resorting to the use of complex spectral functions. A relation is established between the spectral viscoelastic functions and the conditional rheological characteristics.Mekhanika Polimerov, Vol. 3, No. 6, pp. 977–988, 1967