Investigation of the mechanical properties of acrylics under conditions of creep,stress relaxation,and harmonic vibration

The dynamic and static (creep, stress relaxation) mechanical properties of various acrylics have been investigated. A relation is established between the structure and the macroscopic mechanical properties. The previous thermal history and the characteristics of the state of stress are shown to affect the nature of the relaxation processes and the mechanical properties of the acrylics. Generalized stress relaxation curves are constructed. The mechanical glass transition temperatures of the acrylics investigated are determined.Lenin Moscow State Pedagogic Institute. Translated from Mekhanika Polimerov, No. 1, pp. 157–159, January–February, 1973.     

Uniform,uniaxial elongation of polyethylenes

The uniform, uniaxial elongation of polyethylenes of various crystallinity and the effect of strain rate on this process are analyzed. Quantitative relations between the stress, the degree of elongation, and the strain rate are established, and the factors controlling the uniform, uniaxial elongation of polyethylenes are defined.M. I. Kalinin Polytechnic Institute, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 987–992, November–December, 1972.     

Analogues of the Kolosov–Muskhelishvili General Representation Formulas and Cauchy–Riemann Conditions in the Theory of Elastic Mixtures

Analogues of the well-known Kolosov–Muskhelishvili formulas of general representations are obtained for nonhomogeneous equations of statics in the case of the theory of elastic mixtures. It is shown that in this theory the displacement and stress vector components, as well as the stress tensor components, are represented through four arbitrary analytic functions.The usual Cauchy–Riemann conditions are generalized for homogeneous equations of statics in the theory of elastic mixtures.     

Experimental investigation of the impact strength of Caprolon in linear and plane stress

An apparatus for investigating the impact strength of materials in plane stress is described. The results of testing Caprolon in plane stress and linear tension over a broad range of strain rates are presented.Leningrad Kalinin Polytechnic Institute. Translated from Mekhanika Polimerov, No. 2, pp. 332–334, March–April, 1971.     

General criteria of the strength of isotropic media

The limit surfaces of isotropic materials are considered in the invariant spaces of the stress tensor. The general requirements that must be met by limit surfaces are formulated. A three-invariant strength criterion for isotropic media sensitive and insensitive to hydrostatic pressure is given in general form. The convenience of analyzing strength criteria in the two-dimensional space of the base invariants of the stress tensor is demonstrated.Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 251–261, March–April, 1971.     

Questions relating to the design of multilayer glass-reinforced-plastic systems in compression

The stability and states of stress and strain of five-layer orthogonally reinforced and unidirectional systems loaded in compression are investigated. The calculations are based on the system of differential-difference equilibrium equations for a multilayer composite in a complex state of stress [1, 2].All-Union Scientific-Research Institute of Glass-Reinforced Plastics and Glass Fiber, Moscow Region. Translated from Mekhanika Polimerov, No. 6, pp. 1019–1028, November–December, 1973.     

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.     

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.     

State of stress and strain of plates with two equal openings in the presence of high-elastic deformation

The apparatus of the nonlinear theory of elasticity [1–3] is used to investigate the high-elastic deformation of a plate with two equal circular openings and a massive block with two cylindrical channels. Computer-calculated stress concentration factors are given for compressible and incompressible materials.Translated from Mekhanika Polimerov, No. 4, pp. 687–692, July–August, 1969.     

Effect of the starting structure of a polymer on the time dependence of its strength under cyclic loading

The stress dependence of the logarithm of the cyclic life for different modifications of the same polymer is represented by a fan of straight lines that converge upon extrapolation to zero stress at a single point log A_cy, which differs from the analogous extrapolation point log A_st. The possible causes of this effect are discussed.Ioffe Physico-Technical Institute, AS USSR, Leningrad. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1008–1013, November–December, 1968.     

Statistical interpretation of the temperature and stress shift factors

Expressions for the temperature and stress shift factors are derived on the basis of a statistical-probability treatment of the segmental motion of the macromolecules using the theory of energy level transitions. It is shown that in the general case the temperature shift factor should depend on stress, and the stress shift factor on temperature.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 528–531, May–June, 1976.     

Fatigue performance of glass/polyester laminates and the monitoring of material degradation

Experiments are performed on glass/polyester composites under fatigue loading. The stiffness degradation is recorded as an indirect measure of material damage. The stiffness decrease rate is described by a power dependence on stress; this relationship allows the fatigue law to be derived. Stiffness-controlled fatigue curves are generated and presented in an S-N-diagram based on normalized stress (equivalent to strain). Such stiffness controlled fatigue curves can be used as a basis for design criteria for components.Presented at the 9th International Conference on Mechanics of Composite Materials, 17–20 October 1995, Riga, Latvia.Materials Department, Risø National Laboratory, Roskilde, Denmark. Published in Mekhanika Kompozitnykh Materialov, Vol. 32, No. 1, pp. 32–41, January–February, 1996.     

Predicting the Deformability of Expanded Polystyrene in Short-Term Compression

A regressive model is presented for the relationship between the compressive stress and strain of expanded polystyrene (EPS) on a 0–35% strain range. On the whole, the model agrees well with experimental data. A practical way is suggested for determining the coefficients of the model from the known density of EPS plates and their compressive stress at a 10% strain. The model allows one to predict the critical compressive stress and the elastic modulus of EPS.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 157–162, March–April, 2005.     

Calculation of the residual stresses in wound glass-reinforced plastics

The effect of the winding and polymerization conditions on the residual stress distribution in wound glass-reinforced plastic cylinders is subjected to a numerical analysis. The calculations are based on the method proposed in [1]. The computer data are examined and the theoretical and experimental results compared.Moscow Power Engineering Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1026–1030, November–December, 1970.     

Some features of the unwinding of glass-reinforced plastic rings

The reasons for the nonhomogeneity of the material of wound glass-reinforced plastic tubes are discussed. Formulas are given for constructing the shrinkage or temperature stress diagrams for nonhomogeneous tubes by the unwinding method.S. M. Kirov Ural Polytechnic Institute, Sverdlovsk. Translated from Mekhanika Polimerov, No. 6, pp. 1076–1081, November–December, 1973.     

Methods of taking into account the nonlinearity of the deformation properties of the material in calculating thick-walled composite rings

The results of an investigation of the deformation properties of unidirectional composites are presented, and engineering models which take into account the effect of the nonlinearity of the properties in the radial direction on the state of stress of rings under pressure are proposed. The relations obtained are checked theoretically — by means of a refined calculation based on the nonlinear theory of elasticity — and experimentally — by loading rings with internal and external pressure by means of rubber cuffs in specially designed apparatus.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 73–84, January–February, 1976.     

Anisotropy of the mechanical properties of cross-linked poly(n-butyl methacrylate)

Mechanical properties of cross-linked poly(n-butyl methacrylate) synthesized under shear stress are reviewed. The effect of shear stress rate and of the cross-linking agent concentration on the resulting polymer properties was demonstrated.Kiev Branch, All-Union Scientific-Research Institute of Complex Polygraphy Problems in Special Types of Printing. Institute of the Chemistry of High-Molecular-Weight Compounds, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 1, pp. 150–152, January–February, 1972.     

One model of a nonlinear viscoelastic medium,taking into account the influence of accumulated damage

We have proposed extremely simple equations for the state of a nonlinear viscoelastic medium of the inherent type, containing the scalar function of the accumulated damage as one of the decisive parameters. The equations take into account the influence of the type of stress pattern; they also contain the long-term strength condition. Equations of this type permit determination of the stress and deformation patterns developing immediately before failure, which is very important for experimental verification of the theory of long-term strength. The proposed model also takes into account the aging of the material.M. V. Lomonosov Moscow State University. Translated from Mekhanika Polimerov, Vol. 8, No. 2, pp. 241–246, March–April, 1972.     

Evaluating the effectiveness of structural stress concentrators on the surface of polymethylmethacrylate glasses produced by an equivalent mechanical stress raiser

The possibility of determining the parameters of a notch-type mechanical stress raiser which is equal in effectiveness to structural stress concentrators on the surface of flat glasses is indicated.Lenin Young Communist's League Institute of Civil Aviation Engineers, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 181–182, January–February, 1972.     

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.