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     

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.     

On the statistical mechanics of deformable media

Random stress and strain fields are examined in relation to machine parts made of materials of the randomly reinforced fiberglass type subjected to random external loads. The conditions of existence of the principal axes of the fourth-order tensor representing the second-order central moments of a plane random stress or strain field are determined. A method of determining the principal axes and principal values is described. A numerical example is worked.V. A. Steklov Mathematical Institute, Sverdlovsk Branch, Academy of Sciences of the USSR. S. M. Kirov Ural Polytechnic Institute, Sverdlovsk. Translated from Mechanika Polimerov, Vol. 4, No. 4, pp. 618–623, July–August, 1968.     

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.     

Creep of a nonlinear viscoelastic beam bent by a random moment

The moments of the stress distribution are calculated for a beam made of unidirectional glass-reinforced plastic bent by a random moment. The method previously proposed in [1] is used to solve the statistical boundary value problem.V. A. Steklov Mathematical Institute, Sverdlovsk Branch, Academy of Sciences of the USSR, Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 731–734, July–August, 1968.     

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.     

A more precise definition of the method of determining the fatigue life of polymer materials from the reheat temperature

Conclusions 1. The rate of increase in the reheat temperature on the linear segment remains constant (for a periodic loading with higher stress levels) until a critical damage is sustained for the stress in question.2. The magnitude of T_c for a given stress is independent of the loading history, provided the critical damage has not been sustained for this stress.3. With decreasing stress T_c decreases slightly. A method for the accelerated determination of T_c from a single specimen for different stress levels has been developed.4. A method of predicting the fatigue life from the results of short-term tests, which take into account the variation of T_c due to stress level, has been developed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 906–913, September–October, 1977.     

Photoelastic investigation of stress concentrations in model glass-reinforced plastics under static load

The title investigation was carried out using a double-beam polarimeter for studying the stress patterns in "sandwich" models of glass-reinforced plastics. The same experimental technique can be adapted to a wide range of reinforced materials. A comparison of the experimental results with calculations based on the theory for quasi-homogeneous anisotropic plates shows that it is not always permissible to assume that the laminated material has a quasi-homogeneous structure.Translated from Mekhanika Polimerov, No. 4, pp. 711–718, July–August, 1969.     

Analysis of the state of stress of massive multichannel high-pressure chambers

The state of stress of multichannel high-pressure chambers made of polymeric materials with low rigidity is analyzed using the apparatus of the nonlinear theory of elasticity [1, 2].Translated from Mekhanika Polimerov, No. 4, pp. 732–733, July–August, 1969.     

Three-dimensional model of the deformation of twisted multilayered rods of composite materials

Conclusion An analytical approach based on certain assumptions regarding the character of the kinematic relations and equilibrium conditions was developed to calculate the stress-strain state of naturally twisted rods of composite materials. A computer program for calculating the stress and strain parameters in each layer was also developed. The results of calculations performed in accordance with the linearized variant (Eq. (5)) of general relations (4) agree satisfactorily with experimental data within a broad range of acting longitudinal loads. The method that was developed has been widely used in the design and optimization of several types of structures.Translated from Mekhanika Kompozitnykh Materialov, No. 4, pp. 610–614, July–August, 1990.     

Compression of an orthotropic prism

The formulation and mathematically correct solution of a three-dimensional boundary value problem are given. A numerical calculation is presented for a prism of Canadian spruce and the displacement and stress fields are determined.Presented at a scientific seminar on polymer mechanics held in the Mechanics-Mathematics Department of Moscow State University, February 7, 1968.M. V. Lomonosov Moscow State University. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 810–815, September–October, 1968.     

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.     

Methods of exploiting natural internal stresses to strengthen composites

A method of strengthening nonuniformly reinforced composites is proposed. A rational scheme for coordinating the external stress field, the resistance field, and the internal stress field is examined in relation to the case when the internal stresses are caused by shrinkage of the resin.Ural Kirov Polytechnic Institute, Sverdlovsk. Translated from Mekhanika Polimerov, No. 5, pp. 870–875, September–October, 1970.     

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     

Properties of multicomponent polymers systems

In order to design materials having different mechanical properties combined with a permittivity of 2.2–2.6 and tg =2·10^–4-4.10^–4 at 20±1° C and 10⁶ Hz, it is possible to use compositions consisting of polystyrene, polyisobutylene and polyethylene. Projections of the three-dimensional triangular composition-property diagrams are presented for selecting the composition corresponding to spcified properties (hardness at 20 and 50° C and breaking stress and elongation).Central Scientific-Research Institute of Communications, Moscow. Moscow Krupskaya Regional Pedagogical Institute. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 133–1135, November–December, 1968.     

A study of the special features of stress relaxation in irradiated polytetrafluoroethylene

As a result of experimental studies of stress relaxation in polytetrafluoroethylene irradiated with various doses (from 2×10⁴ to 1×10⁶ rads), data have been obtained which make it possible to judge the rate of occurrence of relaxation processes in the polymer. A number of special features have been revealed which distinguish the character of occurrence of relaxation processes in the irradiated and nonirradiated material.Plastics Scientific-Research Institute, Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 148–150, January–February, 1972.     

Resistance of composite flywheel rim to radial tensile stresses from centrifugal forces based on results of pure bending of a rim segment

A method is proposed for evaluating the resistance of a flywheel rim to radial stresses in free rotation. The method is based on loading a rim segment in pure bending and calculating the limiting moment and the corresponding limiting angular velocity. Applicability of the method is substantiated theoretically by investigating the similarity of the radial stress diagrams in rotation and pure bending. The method is verified experimentally for the strained state of a rim segment in pure bending.Translated from Mekhanika Kompozitnykh Materialov, Vol. 29, No. 4, pp. 521–526, July–August, 1993.     

Experimental investigation of the propagation of longitudinal stress waves in optically active polymeric rods

A photoelastic technique has been used to investigate the propagation of longitudinal stress waves in free rods. The experiments have made it possible to establish the mechanism of stress wave formation under impulsive loading, explore the dynamic state of stress of the rod, and estimate the effect of the inelastic resistance of the material.B. E. Vedeneev All-Union Scientific-Research Institute of Hydroengineering, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 68–75, January–February, 1970.     

Effect of the third stress invariant on the characteristic curves of a material

The effect of the third invariant of the stress tensor (deviator) on the stress-strain intensity curve and the Lode diagram is investigated.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 612–617, July–August, 1968.     

Yield surfaces in local strain theory

The initial yield surfaces for biaxial tension and combined tension and torsion are determined on the basis of the local strain theory. The limit surfaces of the resultant stress on a local plane in tension (torsion) are obtained. A plastic strain probability factor is introduced and its values are calculated for various loading paths.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 594–598, July–August, 1971.