Viscoelastic parameters of certain polymers in the temperature interval 4.2–240°K

The principal elastic constants of Nylon 6, Nylon 7, Nylon 6.10, Nylon 11, Nylon 12, PVC, PMMA, polystyrene, and polyvinylfluoride have been calculated from data on the velocity of ultrasonic longitudinal and shear waves measured at a frequency of 5 MHz on the temperature interval 4.2–240°K. It is shown that at cryogenic temperatures the dynamic moduli of elasticity are, to a considerable extent, determined by the characteristics of the chemical structure of the polymers. It is suggested that the Poisson's ratios of the polymers depend on their free volume.Scientific-Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 604–609, July–August, 1973.     

Calculation of the elastic moduli of inhomogeneous materials

The effective shear and bulk moduli of an inhomogeneous medium consisting of isotropic components are calculated on the basis of the theory of random functions. The calculation is made in accordance with the Reuss model in the pair correlation approximation. It is shown that, generally speaking, the true elastic moduli are not equal to the arithmetic mean of the values found by Voigt and Reuss averaging without allowance for correlations. The equality holds only if the mean bulk K and shear moduli are in the ratio K/=4/3.Moscow Institute of Electronic Engineering. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 624–630, July–August, 1968.     

Biaxial orientation of amorphous linear polymers

The dependence of the birefringence and orientation stress on the biaxial stretch ratio and orientation conditions has been experimentally investigated. The temperature dependence of these characteristics is explained in terms of the network structure of amorphous polymers. It is shown that the transformations of the supermolecular structures in the process of biaxial orientation depend on the orientation temperature — at higher temperatures better organized structures are formed. There is a formal relationship between the effect of orientation temperature on supermolecular structure formation and on the relaxation process responsible for the formation of a more thermally stable molecular network.Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 17–23, January–February, 1971.     

Breakdown of high-pressure polyethylene in bulk

The mechanism of polyethylene breakdown in bulk at low initial stresses, relaxing during the breakdown process, is discussed. Optical, electron, and scanning microscopy were used to investigate the surface of disintegrating polyethylene for cable insulation. It was found that in prolonged tests the breakdown surface has an appearance typical for the brittle breakdown of glass polymers. It was also established that in the case of brittle breakdown with clearly expressed mirror-like and rough zones, the disintegration process passess passes through an evident deformation of the surface layer and the formation of micronecks prior to rupture.Translated from Mekhanika Polimerov, No. 5, pp. 935–936, September–October, 1972.     

Shear of orthogonally reinforced spherofibrous composites

The problem of determining the shear characteristics and interphase stress concentration of fibrous composites with spherical inclusions is examined on the basis of a three-phase model. Stress fields caused by diffusion interaction of phases are neglected. The elastic moduli of the composite are investigated and compared with those obtained from a two-phase model. The general formula for determination of the shear modulus of triorthogonally reinforced compsites is derived using previously investigated relationships for averaged stress fields. The matrix of these compsites contained spherical cavities. The dependence of integral characteristics of three-phase composites on their bulk phase concentration was investigated. The stresses between phases were studied as a function of composite structure.A. A. Blagonravov Machine-Science Institute, Russian Academy of Sciences, Moscow, Russia. Translated from Mekhanika Kompozitnykh Materialov, No. 1, 104–111, January–February, 1997.     

Elastic properties of certain polymer matrices at low temperatures

A study is made of the viscoelastic behavior of the polyimide DFO and polybenzoxasol (PBZ) at low temperatures. Pulsed ultrasound is used to measure ultrasonic velocity in polymers at the frequency f=5 MHz within the temperature interval 4.2–240 K. Data obtained from acoustic measurements is used to calculate the dynamic elastic modulus, shear modulus, compressive bulk modulus, Poisson's ratio, and certain thermophysical characteristics (Debye temperature, specific heat, coefficient of linear expansion, Grünheisen parameter). It is established that the investigated polymers have low dynamic moduli at 4.2 K. Their values change by 18–20% within the temperature range 4.2–240 K. The polymers also have a large free volume at the temperature of liquid helium. The results show that polyimide DFO and PBZ have good service properties at low temperatures.Paper presented at the IX International Conference on the Mechanics of Composite Materials, Riga, October, 1995.Moscow State Academy of Automotive and Tractor Engineering, Russia. Translated from Mekhanika Kompozitmykh Materialov, No. 4, pp. 454–459, July–August, 1996.     

Second-approximation shear theory for shallow layered shells and plates

Analysis of a second-approximation refined shear model for shallow layered composite shells and plates with a substantially inhomogeneous structure over the thickness is presented. The tangential displacements and corresponding normal stresses are expressed in the form of a polynomial of the fith degree in the transverse coordinate and contain squared rigidity characteristics. In this way, the accuracy of results and practical coincidence with the 3D solutions is ensured. Based on the refined model, a theory of shallow layered shells is developed. A system of resolving equations of sixteenth power together with appropriate boundary conditions was obtained and solved analytically. It is shown that the area of application of the formed model is extended as compared with the model of the first approximation. The model proposed allows us to examine the stress-strain state of layered composite structures of substantially different thickness and physical-mechanical characteristics of the layers, including the possibility of simulating relatively large shear deformations of rigid layers separated by a low-modulus thin interlayer pliable to transverse shear.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Ukrainian Transport University, Kiev, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 3, pp. 363–370, May–June, 1998.     

Rheological properties of polymers in the fluid state

The possibilities and conditions of correlation are determined for the principal rheological characteristics of single-phase polymer systems measured for one-dimensional shear deformation in steady-state flow regimes, on transition from rest to steady-state flow, and in harmonic vibration regimes. Special significance attaches to the quantitative results of measuring the high-elastic properties of the polymer systems. It is shown that the Lodge theory, describing the flow behavior of high-elastic media, is well-founded in the linear region of deformation, i.e., for the limiting case of shear rates and shear stresses tending to zero, whereas the Mooney-Rivlin-Weissenberg theories are not in accord with the experimental data even in this limiting deformation regime.Topcheiv Institute of Petrochemical Synthesis, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, Vol. 5, No. 1, pp. 164–181, January–February, 1969.     

Lamellar structure and plasticity micromechanisms in bulk crystalline polymers. Communication 2

Conclusions 1. It has been experimentally established that the deformation of crystalline polymers is accompanied by the shear transitions between lamellar crystals of different orientations characteristic of martensitic structures.2. It is concluded that the reversibility of the large deformations of linear polymers is martensitic in nature.For communication 1 see [1].E. O. Paton Electrowelding Institute, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 6, pp. 963–969, November–December, 1976.     

Dynamic bending of plates with low shear strength

The dynamic problem of the natural vibrations of glass-reinforced plastic plates with low shear strength is examined. The calculations are based on the Timoshenko model (allowance for shear strains and rotational inertia). It is shown that disregarding effects associated with the large shear compliance of glass-reinforced plastic plates leads to appreciable errors in determining the dynamic characteristics.Institute of Polymer Mechanics, Academy of Sciencies of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 698–704, July–August, 1968.     

Viscosity,rubber elasticity,and viscoelasticity of concentrated polymer solutions

The results of a comparative investigation of the effect of the nature of the polymer and the solvent on the viscosity, rubber elasticity, and viscoelasticity of concentrated polymer solutions in the region of linear mechanical behavior are presented. It is established that in the case of nonpolar polymers the solvent affects only the free volume of the solution, whereas for polar polymers it also affects the entanglement network. This leads to the equality of the viscosities of solutions of nonpolar polymers in different solvents when compared in corresponding states (relative to the glass transition temperature) and to the dependence of the shear modulus of solutions of polar polymers on the nature of the solvent and temperature. It is shown that there is a universal relaxation spectrum in the flow zone for solutions of different polydisperse polymers after normalization with the shear modulus and the natural relaxation time determined as the ratio of the viscosity to the shear modulus.A. M. Gor'kii Ural State University, Sverdlovsk, A. V. Topchiev Institute of Petrochemical Synthesis, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 729–736, July–August, 1973.     

Multicritical phenomena in flow of viscoelastic liquids. 3. Liquid-crystalline polymers. The Akay-Leslie anisotropic liquid. Viscometric functions

The advances in determination of the rheological material functions of liquid-crystalline polymers (LCP) in a wide range of concentrations or temperatures are briefly examined. Special attention is focused on a discussion of the concentration region of the existence of liquid-crystalline order and textures initiated by shear flow. The phenomenological rheological equation for an anisotropic liquid proposed by Akay and Leslie (A-L model) was selected for describing the flow resistance of LCP, and the problem of simple shear flow of a liquid was solved. It was shown that the A-L model can describe all of the basic characteristics of the viscometric functions of LCP, including the phenomenon of negative values of the first normal stress difference for some range of concentrations and shear rates. The available data on the initial viscosity of lyotropic LCP were classified based on the types of cohesion (dimensionality) of the system, characterized by the exponent of the concentration dependence of the viscosity. It was found that each type of cohesion has its own kind of viscometric functions and that the A-L rheological model can reflect their basic characteristics. It was shown that by varying the initial ordering parameter of the A-L model, linear (or almost linear) functions N₁(q) and ₁₂(q) can be described in the region of low shear rates. It was hypothesized that region 1 of the flow curve (Onogi and Asada) inevitably exists in the continuous liquid crystalline phase, which could be outside of the region of measurements accessible to rheometry.See [23] for Communication 2.Institute of Polymer Mechanics. Riga. LV-1047 Latvia. Translated from Mekhanika Kompozitnykh Materialov. No. 6. pp. 821–839. November–December, 1997.     

Effect of fiber tension on the unwinding resistance of hardening layers of glass-reinforced plastic

The shear fracture toughness characteristics of glass-reinforced plastics used for strengthening metal pressure vessels have been determined by testing metal-GRP rings. The shear fracture toughness characteristics are statistically estimated for a unidirectional GRP as a function of the winding tension.K. É. Tsiolkovskii Moscow Aviation Engineering Institute. Translated from Mekhanika Polimerov, No. 5, pp. 935–938, September–October, 1975.     

Rheological characteristics of orthotropically reinforced polymeric materials

It is proposed to calculate the rheological characteristics of orthotropically reinforced polymeric materials using a model in accordance with which the composite is assumed to consist of layered blocks, the planes of the layers having one of three possible orientations with given probabilities. The effective rheological characteristics of each block are exactly determined, while those of the composite as a whole are determined in the Voight or Reuss approximations. The first scheme is convenient for calcuating the shear modulus operators, the second for calculating the Young's modulus and Poisson's ratio operators. A numerical computer analysis has been made for the Young's moduli. It is shown that for the anisotropic composites in question each of the technical elastic moduli is characterized by two resolvent Q* operators of real or complex argument. The conditions under which one of the Q* operators can be neglected are determined. The integral representation of the kernel of the Q* operator of complex argument is given in the case where the latter is fractional-exponential with fractional index =–1/2 and the corresponding curves are presented.Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 276–283, March–April, 1972.     

Bending features of a sandwich panel with asymmetric structure under local loads

The bending characteristics of a composite panel with asymmetric layered structure under local surface loads are obtained. A refined version of the applied theory is developed using the analytical solution of the bending problem of a sandwich plate with arbitrary asymmetric structure under a point load. Local effects are investigated within the limits of a discrete model allowing for the specific character of elastic properties of a soft filler. The advantages of the solution are expressions of bending characteristics — layer curvatures, displacements, and stresses — in a closed form. It is shown that these characteristics can vary several times depending on the asymmetry parameters of the structure. Degeneration peculiarities of the solution, stemming from the slipping of layers or, otherwise, their rigid linking by the Kirchoff—Love hypothesis, as well as from account of the transverse shear and compression of the normal, are examined in line with the degeneration of geometric and physical parameters of the discrete model adopted. The results obtained are illustrated by curves and surfaces for the characteristics studied.Submitted for the 11th International Conference on the Mechanics of Composite Materials (Riga, June 11–15, 2000).Institute of Polymer Mechanics, Latvian University, Riga, LV-1006 Latvia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 6, pp. 717–742, November–December, 1999.     

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.     

Physical and physicochemical modification of polymers

Research on the modification of the properties of crystalline polymers by changing their physical structure is reviewed. Two different modification principles are considered — the creation of a homogeneous physical structure (introduction of small amount of highly dispersed regulators of the structure-forming processes) and the creation of an inhomogeneous physical structure (by contact with large regulating surfaces) in order to differentiate the surface from the bulk properties and improve resistance to the development of defects. The question of regulation of the processes of physical structure formation by the introduction of chemically reacting substances is also investigated. The possibilities of using antioxidants as physical modifiers and the possibility of physical modification during both the processing and synthesis of polymers are stressed.L. Ya. Karpov Scientific-Research Physicochemical Institute, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 395–408, May–June, 1972.     

Control of the mechanical properties of polymers by modification of their supramolecular structure

Modern ideas on the main types of supramolecular structure in polymers and their various characteristics are discussed, and the possibility of controlling these formations by introducing small amounts of finely dispersed solids is considered. It is noted that crystalline polymers containing artificial nuclei are more resistant to the action of heat and various mechanical influences.Mekhanika Polimerov, Vol. 2, No. 5, pp. 643–650, 1966Presented at the First Conference on Polymer Mechanics (Riga, November 1965).     

The acoustic properties of polymers with an asymmetric potential barrier at liquid-helium temperatures

The pulse-phase compensation method has been used to measure the propagation velocities of longitudinal and shear waves in polyvinyl chloride, polyvinyl fluoride, and polystyrene at frequencies of 1 and 5 MHz on the temperature interval 2.1–240°K. It has been established that as the temperature falls to 2.1°K the speed of ultrasound in these polymers monotonically increases, the dispersion (frequency dependence) of the speed of sound being preserved over the entire temperature interval. Two possible causes of the viscoelastic relaxation observed in the investigated polymers in the region of helium temperatures are considered.Scientific-Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 749–751, July–August, 1973.     

Study of the impact shear strength of polymer materials

A method is proposed for studying the dynamic strength of block polymers in terms of their resistance to impact shear. An original instrument for conducting tests are room and elevated temperatures is described. The results obtained with this instrument for alkathene and styrene carylonitrile copolymer are discussed. It is found that there is a considerable increase in specific shear energy in the region of transition from the glassy to the high elastic state. In the case of alkathene the investigated characteristic falls linearly on the temperature interval studied.Leningrad Kirov Institute of the Textile and Light Industries. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1135–1137, November–December, 1968.