Effect of long-term storage of polycarbonates on stress relaxation

The effect of long-term storage (three-five years) on the mechanical properties of polycarbonates and Makrolon has been experimentally investigated under conditions of stress relaxation at normal and elevated temperatures.Scientific-Research Institute of Mechanics, Lomonosov Moscow State University. Translated from Mekhanika Polimerov, No. 1, pp. 149–151, January–February, 1973.     

Notch sensitivity of polymethyl methacrylate

It is shown that acrylics have a notch sensitivity determined by the nature of the state of stress produced by the loading.Lenin Riga Komsomol Institute of Civil Aviation Engineers. Translated from Mekhanika Polimerov, No. 3, pp. 562–564, May–June, 1971.     

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     

Effect of the type of state of stress on the characteristics of the mechanical glass transition process in polymers

The effect of the type of state of stress on the activation energy and relaxation time is investigated with reference to the mechanical glass transition (softening) process in polymers. An expression relating the mechanical glass transition temperature with the structural glass transition temperature, the mean stress, and the stress intensity is obtained for isotropic homogeneous polymers. Experimental data obtained for polymethyl methacrylate in uniaxial tension and compression, pure bending, and shear are presented.All-Union Scientific Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 195–199, 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.     

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.     

Stress relaxation in a polymer disk

The stress relaxation in a polymer disk with a central hole, into which a rigid metal rod is press-fitted, is considered. The progressive redistribution of the stresses in the disk has been observed by a photoelastic method. In the theoretical solution of the problem the relaxation properties of the polymer are taken into account by means of a generalized nonlinear Maxwell equation with two terms of the relaxation spectrum. It is shown that the linear, as distinct from the nonlinear, theory is not capable of conveying the characteristics of the stress relaxation process in a rigid polymer disk.Institute of Chemical Physics, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1064–1070, November–December, 1971.     

Study of behavior of plastics during production and aging. Polycaprolactam

The effect of molding conditions on the mechanical properties of polycaprolactam (nylon-6) is examined, together with the variation in these properties with time. The experimental data lead to the conclusion that the mechanical properties of polycaprolactam depend on the degree of interaction between two processes: relaxation of the internal residual stresses and the ordering of the structure.Mekhanika polimerov, Vol. 1, No. 1, pp. 17–25, 1965     

Mechanical relaxation processes in polymers

The various kinetic processes are classified and the place of relaxation effects among them is established. The theoretical basis of mechanical relaxation phenomena in polymers is outlined. The characteristics of relaxation processes associated with molecular mobility are examined with reference to various classes of polymers, in particular, amorphous and crystalline polymers, copolymers, and mechanical mixtures. The characteristics of relaxation processes associated with rearrangement of the supermolecular structures in amorphous and crystalline polymers are considered.This article is a review of mechanical relaxation effects in polymers with particular attention to research conducted in the Problem Laboratory of Polymer Physics of the Moscow Lenin State Pedagogical Institute.Problem Laboratory of Polymer Physics, Lenin Moscow State Pedagogical Institute. Translated from Mekhanika Polimerov, Vol. 5, No. 1, pp. 30–53, January–February, 1969.     

Features of viscoelastic behavior of materials based on heat-resistant polymers

Conclusions In the example of polybenzoxazole, the relationships of viscoelastic behavior have been investigated for monolithic heat-resistant polymers over a wide range of temperatures (from 22° to 230°C) and initial deformations (from 0.5 to 2.5%). The experimental data on stress relaxation, covering the regions of linear and nonlinear viscoelasticity, are approximated by the basic equation of the primary cubic theory of Il'yushin, using the singular kernel of Rzhanitsyn. For the first time, the region of stable mechanical capability of monolithic heat-resistant polymers has been defined with due regard for relaxation characteristics.Paper presented at Fourth All-Union Conference on Polymer Mechanics and Composite Materials (Riga, October 1980).Translated from Mekhanika Kompozitnykh Materialov, No. 6, pp. 978–983, November–December, 1980.     

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     

Deformation of elastic polyurethanes with a bimodal cellular structure

This article examines the cellular structure and mechanical properties of elastic foamed polyurethanes with a bimodal cellular structure (BFPUs). It is shown that the sizes of the oval cells (3–12 mm) in the elastic foamed polyurethenes that are studied are a tenth of an order greater than the sizes of the polyhedral cells (0.1–0.6 mm). Conversely, for rigid foamed polyurethanes, the polyhedral cells are more than a tenth of an order larger than the oval cells (microcells). The equations of the compression curve of BFFUs are found, and it is established that the deformation of BFPUs is determined by the deformation function of the cellular structure and the viscoelastic properties of the polymer matrix. The deformation functions of the cellular structure and the relaxation properties of BFPUs are determined. It is shown that choosing BFPUs with a cellular structure improves the comfort properties of the foamed material: the softness coefficient increased by 8–19% in the investigated case, while the support coefficient increased by 15–35%.Paper presented at the IX International Conference on the Mechanics of Composite Materials (Riga, 1995).Translated from Mekhanika Kompozitnykh Materialov, Vol. 32, No. 3, pp. 330–339, May–June, 1996.     

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     

On the theory of anisotropic creep of unidirectional glass-reinforced plastics

The basic relations of the theory of anisotropic creep of unidirectional glass-reinforced plastics (GRPs) in a three-dimensional stress state are found using a model of a material with inhomogeneous structure and the rheological properties of the resin. These relations are suitable for investigating the stress state of GRPs for resin stresses not exceeding certain values. The phenomena of simple creep and stress relaxation are studied with reference to a unidirectional GRP with an epoxy-maleic resin matrix.Mekhanika Polimerov, Vol. 1, No. 2, pp. 64–69, 1965     

Macromolecular mechanics

The fundamentals of "macromolecular" mechanics are outlined and approximate quantitative relations are established between the parameters of the mechanical properties of elastically stretched macromolecules and the characteristics of the mechanical properties of polymers determined at significant uniaxial deformations. This new scientific approach is based on the assumption of "framework connectivity." The conditions of internally compensated mechanical equilibrium at the molecular level are investigated. Several variants of simple geometric models of the "framework" reinforcing the stretched polymer are proposed. A system of quantities characterizing the mechanical properties of the polymer and the "framework" is developed. According to the theory, the stress in the "framework" macromolecules, considered as a molecular elastic continuum, substantially exceeds the stress in the stretched polymer. The nature of the internal stresses and elastic aftereffect in glassy crystalline polymers subjected to significant deformation is reinterpreted.Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 221–231, March–April, 1971.     

Variation of the elasticoviscous characteristics of a heavily filled rubber after periodic shear deformation

The results of an investigation of the recovery of the elasticoviscous characteristics after thixotropic reduction by periodic deformation in the nonlinear zone are reported. The rate of recovery of the mechanical properties depends on the deformation frequency and the previous history of dynamic deformation is shown to affect the dependence of the elasticoviscous characteristics on the shear rate gradient. The effects of stationary and dynamic deformation regimes on the relaxation spectrum of the material are compared.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 528–533, May–June, 1969.     

Estimation of the molecular characteristics of polymers by the SPRT method and study of their influence on the properties of compositions

Pressure relaxation was examined in the cylinder of an MPT Monsanto processability tester after stopping the piston. The experimental function of the pressure drop F(t) was smoothed over and approximated by cubic splines. The spectra of pressure relaxation times (SPRT) were obtained according to the method of Schwarzl-Staverman. The SPRT method served well for estimating the spectra of the molecular-mass distribution (MMD) of polymers close in their physical sense to the SPRT. The correlation of the characteristic relaxation times and average molecular mass of ethylene-propylene rubbers and polyethylenes obtained by gel permeation chromatography was approximated by optimum models used for calculating the the molecular mass of rubbers according to the measurement results of the relaxation pressure of melts. The SPRT and characteristic relaxation times were used to analyze the significant technical properties of compositions based on polyethylene and rubber. The SPRT method was used to examine the failure of the cure network of butyl rubber and the dependence of the mechanical properties of thermoplastic elastomers on the molecular features of the decomposite.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Kazan State Technological University, Tatarstan, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 5, pp. 691–698, September–October, 1998.     

A type of mechanically anisotropic,optically sensitive material

The technology for obtaining a mechanically anisotropic, optically sensitive material that can be used in photoelastic stress analysis is described. The mechanically anisotropic, photoelastic materials obtained by this method (method 3) are free of initial birefringence, have a sufficiently high degree of mechanical anisotropy, and possess high optical sensitivity. The elastic and piezooptic properties of specimens of orthotropic material have been investigated and it has been found that the isochromatics (lines of equal path differences ) are lines of equal principal strain differences. Experimental results are presented for the stress distribution in an orthotropic disk compressed by a pair of opposing concentrated forces.Translated from Mekhanika Polimerov, No. 5, pp. 835–839, September–October, 1971.     

Effect of molecular mobility,state of stress,orientation, and plasticization on the temperature dependence of the mechanical properties of linear polymers

The temperature dependence of the breaking stress and ultimate creep strain has been investigated in relation to preorientation, plasticization, and state of stress for polymethyl methacrylate, high-pressure polyethylene, polystyrene, and polyvinyl alcohol. The results of the mechanical tests are compared with the NMR data on the molecular mobility. The causes of the observed effects are discussed.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 30–35, January–February, 1971.     

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.