Effect of supermolecular structure on the relaxation properties of polyformaldehyde in tension and compression

An experimental investigation of the stress relaxation at various strain values in polyformaldehyde blocks has revealed two regions with different stress relaxation mechanisms. The effect of the supermolecular structure on each of these regions is discussed.Scientific Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 787–792, September–October, 1969.     

Calculation of relaxation spectra from dynamic test data

A procedure is proposed for calculating relaxation spectra from experimental data on uniaxial tension over a broad range of strain rates. The relaxation spectra are calculated for low-density polyethylene and for a fabric-reinforced glass laminate in three directions relative to the reinforcement.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 349–353, March–April, 1971.     

Relaxation and optical properties of cured epoxy resin

Epoxy resin cured with methyltetrahydrophthalic and maleic anhydrides has been tested in relaxation, creep, and compression at constant strain rate. The constants characterizing the relaxation properties and the approximate limits of the spectrum of most probable relaxation times have been determined; it is shown that the mechanical properties can be described by means of equations with two relaxation times. The residual optical effect has also been investigated. A linear relationship between the high-elastic strains and the path difference in the birefringent state is preserved at temperatures below the glass transition region.Read at Moscow State University polymer mechanics seminar.Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 15–23, January–February, 1970.     

Stress relaxation in glassy polymers

Stress relaxation in amorphous linear polymers has been investigated below the glass transition point at various strain rates, temperatures, and strains. A model of a nonlinear viscoelastic body is proposed as a means of describing the effect. It is shown that stress relaxation is well described by the model considered and is correlated with the deformation characteristics of the polymers.A. F. Ioffe Physico-Technical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 987–994, November–December, 1971.     

On the theory of orientation of linear amorphous polymers

The previously derived orientation equations are solved for uniaxial extension at constant true stress, unloading, stress relaxation, and biaxial orientation at constant strain rate. The dependence of the birefringence of biaxially oriented PMMA on the magnitude and conditions of preliminary orientation has been experimentally investigated. There is good qualitative agreement between the theoretical and experimental results.For communication 1 see [1].Lenin Moscow State Pedagogic Institute. Translated from Mekhanika Polimerov, No. 1, pp. 14–21, January–February, 1973.     

Relaxation phenomena in rubber-like polymers with small deformation above the glass transition temperature

In the temperature region in which rubber-like polymers have a high elasticity, a high-temperature subregion has been observed which is characterized by the presence on the extension curve of a critical strain at a small deformation (1–2%). The rigidity of the polymer below and above the critical value is different. The relaxation character of this phenomenon is considered.V. I. Lenin Moscow State Pedagogical Institute. Laboratory of Polymer Physics Problems. Translated from Mekhanika Polimerov, No. 3, pp. 544–546, May–June, 1970.     

Experimental investigation of the correspondence between quasistatic tension and longitudinal wave propagation in a polyethylene rod

The propagation of longitudinal waves created by the impact of a rigid mass against a polyethylene rod of finite length has been investigated. The experimental procedure is described and oscillograms of the process are presented. The relaxation spectrum is calculated from the experimental data on the mechanical behavior of the material over a broad range of strain rates. The results of the experiments are compared with a numberical solution of the problem of the impact of a rigid mass against a rod whose material is characterized by a relaxation spectrum.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 564–567, May–June, 1971.     

The relationship between stress and deformation of polymers in the linear stress state

The relation between stress, strain and strain rate is proposed as a means of describing the deformation properties of polymers. The equation describes the stress-strain curve, aftereffect, and stress relaxation in polymers. The theoretical conclusions are in good agreement with the results of creep tests on kapron (nylon-6).Mekhanika Polimerov, Vol. 1, No. 5, pp. 25–29, 1965     

Graphoanalytical method of calculating the mechanical characteristics of a material from the stress relaxation at constant strain

A graphoanalytical method of calculating the stress relaxation curves at constant strain is described. By its means the constants characterizing the mechanical properties of polymers can be easily and rapidly determined.Mekhanika Polimerov, Vol. 1, No. 6, pp. 15–19, 1965     

Intensity of the relaxation processes in statically loaded,highly oriented synthetic fibers

An experimental study of the stress relaxation and creep of a series of synthetic fibers has revealed a reduction in the intensity of these processes as the tensile strain increases. On the basis of a comparison of the relations obtained and the results of previous studies of loaded oriented polymers using small-angle x-ray scattering and NMR techniques it is suggested that the observed effect is attributable to orientational ordering of the through macromolecules in the amorphous regions of the fiber. It is also concluded that in oriented polymers at strains considerably below breaking values the elementary relaxation events are physical (and not mechanochemical) in nature.Kirov Leningrad Institute of the Textile and Light Industries. Translated from Mekhanika Polimerov, No. 1, pp. 154–157, January–February, 1973.     

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     

Nonlinear shear response of fluid polymers during periodic deformation. Basic harmonics

Conclusions 1. A model with a relaxation spectrum independent of accumulated elastic strains describes the combination of data on the amplitude and frequency dependences of the components of the shear modulus in terms of basic harmonics for low-molecular-weight polyisobutylene and a filled-polyethylene melt.2. The greater the amplitude of the shear strain, the broader the region of invariance of the relaxation functions relative to the amplitude of the rate of oscillatory shear.3. The kinetic (s) function affects the amplitude dependences of the modulus in terms of basic harmonics. Its effect is significantly greater on the real component of the modulus than on the imaginary one.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1093–1100, November–December, 1977.     

Relaxation processes in oriented amorphous polymers

Values of the birefringence and high-elastic strain are presented for amorphous polystyrene subjected to stretching and annealing. The laws of the relaxation processes that occur in linear polymers under these conditions are discussed.Mekhanika Polimerov, Vol. 2, No. 3, pp. 323–329, 1966     

On the number of relaxation regions in polyformaldehyde

The mechanical relaxation of a polyformaldehyde homopolymer free from surface grease and the additives normally used as stabilizers has been studied at a frequency of 10^–2 Hz in the temperature region 77–413°K. Six relaxation regions are observed on the curve of tangent of angle of mechanical losses as a function of temperature.T. G. Shevchenko Kiev State University. Translated from Mekhanika Polimerov, No. 5, pp. 925–927, September–October, 1973.     

Uniaxial extension of polystyrene with a constant true stress

A apparatus designed for the extension (stretching) of yielding polymers at a constant true stress is described. The changes taking place in the general, rubber-elastic, and irreversible deformations aredetermined, together with the corresponding rates of deformation, as well as the viscosity and relaxation characteristics, during the extension (tensile strain) of block polystyrene at various constant true stresses and a temperatore of 130°C.All-Union Scientific-Research Institute of Synthetic Fiber, Kalinin. Translated from Mekhanika Polimerov, No. 6, pp. 1104–1109, November–December, 1972.     

Influence of temperature and humidity on the creep of polymer materials

Conclusions By analyzing the results of the original creep tests under shear and tensile conditions subject to various temperatures and humidities, and also analyzing some control experiments involving simultaneous shear and tensile strain, we have shown that the displacement function of the relaxation spectrum expressing the maintenance of the temperature-humidity-time analogy is independent of the form of the stressed state in the range of linear viscoelasticity for a Poisson coefficient close to 0.5.For Communication 2 see [2].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 627–632, July–August, 1976.     

Calculation of damage and of force relaxation in amorpho-crystalline polymers

The dynamics of damage and of the relaxing force in amorpho-crystalline polymers under constant strain are calculated using the formulas for the probability of rupture of a deformed polymer molecule and a model representation of amorphous interlayers. The main parameters of the model are the maximum and minimum possible deformations of molecular chains, the energy of rupture activation, the function of the chain length distribution, the temperature, the macroscopic strain, and the relative dimensions of the amorphous interlayer. The conformity of the theoretical model and the association of the relaxation spectrum with the internal molecular and structural characteristics of the material are established.Zhambyl Technical Institute of Light and Food Industry, Taraz, Kazakhstan. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 4, pp. 499–508, July–August, 1999.     

Determination of the distribution function of the dielectric relaxation times of polymer materials

An exposition is presented of a phenomenological theory of dielectric relaxation. A brief review is given of the existing procedures for finding the distribution function of the dielectric relaxation times. A procedure is suggested for determining the distribution of the relaxation times of polymer materials from an experimentally measured current-decay function by means of the numerical solution of an integral equation on a computer.Institute of the Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 348–353, March–April, 1976.     

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.     

Equations of three-dimensional deformation of linear viscoelastic media

An equation is proposed relating the stress and strain tensors in time for the three-dimensional deformation of linear viscoelastic media whose properties are determined by four parameters. A method is indicated for determining these parameters based on simple creep or relaxation tests. Values of the parameters are given for certain polymer materials. For such materials, there is an upper limit of the stress state below which an equilibrium limit state is possible. A creep kernel is proposed for the case of no equilibrium limit state, and a resolvent constructed with account for the variation of stress and strain in time.Mekhanika Polimerov, Vol. 1, No. 4, pp. 35–42, 1965