Acoustic fatigue of polymer materials

Methods are proposed for experimentally estimating the temperature-time aging of a filled rubber and the degree of damage accumulation in high-frequency fatigue tests. A procedure for experimentally determining the energy dissipation function of a material from the specimen temperature kinetics is described. The results of an investigation of the fatigue properties of two series of filled rubbers at a vibration frequency of 20 kHz are presented. It is shown that the fatigue failure of the materials tested is thermal in character. No accumulation of mechanical damage in the material in the course of intense vibration could be detected.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 662–668, July–August, 1969.     

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.     

Change in the optical properties of ski-3 rubber in deformation,fatigue, and thermal and radiation aging

Conclusion Optical methods can be used in studying the kinetics of mechanical fatigue, thermal, and radiation aging; some general characteristics and differences in the development of these processes in elastomers with higher extinction can be detected with them. The sensitivity of the measurements is increased by the rational selection of the light wave-length of preliminary homogeneous biaxial stretching. A decrease in the thickness attained by deformation by one order of magnitude did not convert the optical medium to the class of singly scattering media, but the changes in the optical properties in aging were more pronounced against the background of decreasing extinction.Translated from Mekhanika Kompozitnykh Materialov, No. 2, pp. 261–265, March–April, 1991.     

Mathematical modeling of temperature pulsation in a thick anode in optoelectronic systems

A numerical method is applied to analyze the one-dimensional model of temperature pulsation inside a two-layer anode with temperature-dependent thermophysical coefficients. The analysis allows for surface thermal radiation, secondary electron emission, and distribution of electron energy losses by penetration depth into the target. Penetration of pulsations deep into the target is observed.Translated from Matematicheskoe Modelirovanie i Reshenie Obratnykh Zadach Matematicheskoi Fiziki, pp. 215–217, 1993.     

Damping properties of soft viscoelastic materials for certain combinations of a planar stress distribution

The results of experimental studies of the energy scattering by soft, viscoelastic materials with certain combinations of a planar stress distribution, established by the superposition of a cyclic shear on tension-compression, are given. Special graphs were used for evaluating the damping properties of the materials, i.e., lines of equal damping, which enabled the equivalent uniaxial stress to be found for each combination of planar stress distribution, which produced the same specific scattering of energy. It is shown that the use of the superposition principle for calculating the mechanical losses in a planar stress distribution from experimental data obtained in uniaxial cyclic loading leads to large errors.Volgogradskii Polytechnic Institute. Translated from Mekhanika Polimerov, No. 6, pp. 999–1005, November–December, 1972.     

Study on the impact-shear viscosity of block polymers

The temperature dependence of the specific impact viscosity of several amorphous and amorphous-crystalline polymers as measured in tests by means of the authors' impact-cutting method is discussed. It is shown that this dependence agrees fairly well with the mechanical losses determined at the same interaction frequencies and, hence, is sensitive to the relaxation transitions in polymers (an enhanced impact stability corresponds to the transition regions). The similarity mentioned above and the correspondence between the temperature dependences of the density, the Poisson coefficient, and the elasticity modulus suggests that mechanical energy supplied is dissipated by a molecular-motion type including segment motion and relating to melting of the crystallites.S. M. Kirov Leningrad Institute of Textile and Light Industry. Translated from Mekhanika Polimerov, No. 2, pp. 226–230, March–April, 1972.     

Investigation of the energy effects accompanying the elastic deformation of uniaxially oriented crystalline polymers

The energy (thermal and mechanical) effects accompanying the elastic deformation of uniaxially oriented crystalline polymers have been investigated; it has been established that, when these polymers are stretched, heat is released. It is shown that the heat release in uniaxial tension is a consequence of localization of the elastic deformation in the poorly ordered regions of the polymer. The relation between the thermoelasticity of uniaxially oriented crystalline polymers and their supermolecular structure is examined.Institute of Heteroorganic Compounds, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 785–798, September–October, 1970.     

Relationship between the molecular structure and certain mechanical properties of oriented polymers

The correlations between the molecular structure and intermolecular energy and the fatigue and elastic properties of fibers are considered. It is shown that the maximum of these properties corresponds to an optimal value of the intermolecular energy.Leningrad Branch of the All-Union Scientific-Research Institute of Synthetic Fibers. Translated from Mekhanika Polimerov, No. 4, pp. 734–735, July–August, 1969.     

Change in the properties of the membrane of the left ventricle of an artificial heart after operating in an animal

Conclusion After 53-day operation of a biomer membrane of an AH in a calf its physical and mechanical properties changed little. The membrane retained the greater part of its fatigue life and a high surface quality; as a consequence of insignificant creep, its functional properties also changed little.Translated from Mekhanika Kompozitnykh Materialov, No. 3, pp. 533–536, May–June, 1985.     

Accumulation of fatigue defects in polymethyl methacrylate in rotational bending

The results of tests on polymethyl methacrylate for fatigue during polycyclic rotational bending through an angle under thermostatic conditions are analyzed. A method of calculation is given for the determination of the defects. The observed changes in the mechanical characteristics and the fractography of the fractures are taken into account comprehensively. Possibilities for the simplification of the method of calculation, and the acceptable methods for the indication of defects before the formation of the main crack are discussed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1038–1045, November–December, 1974.     

Polymer breakdown and fatigue

Problems of the mechanical breakdown of polymer materials are discussed on the basis of kinetic considerations on such breakdown, viewed as a thermofluctuation-induced process of an accumulation of breaks in interatomic bonds (either break or damage). The present state of this problem is analyzed, both for static and for cyclic loads (fatigue). Some approaches for developing a theory of breakdown are reviewed. Theories related to the accumulation of damage in the volume of the sample receive particular attention. Recent studies on fatigue in polymer materials are listed.Paper presented at the 2nd All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1971.A. I. Ioffe Physicotechnical Institute, Academy of Sciences of the SSSR, Leningrad. Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 597–611, July–August, 1972.     

Molecular mobility in polymers under cyclic loading

Using the NMR method the authors have investigated thermal molecular movement in polymers under the conditions of fatigue tests. They have found that the increase in molecular mobility under cyclic loading (cycle frequency 1–10 Hz) is due only to general self-heating of the polymer. Heating of the specimens as a result of hysteresis heat release takes place uniformly throughout the volume.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 1035–1038, November–December, 1972.     

Apparatus for testing samples of glass plastic subject to high-frequency fatigue in the symmetrical extension-compression mode

Using an instrument of the UM-20 type (made by the Scientific-Research and Design Institute of Testing Instruments, Moscow) as a basis, an apparatus is designed for subjecting glass-plastic samples to high-frequency fatigue tests at frequencies of 10–20 kHz. In order to stabilize the thermal state of the sample, water cooling is incorporated.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 756–758, July–August, 1972.     

Current state and prospects for development of the physical theory of brittle strength of polymers

Various mechanisms of brittle fracture and theories of the time dependence of the strength of rigid polymers are examined. The effect of various types of mechanical losses (deformation, dynamical, surface) on polymer strength and life is analyzed. The principal shortcomings of Griffith's theory of strength are pointed out. From an examination of the two basic mechanisms of brittle fracture of polymers-nonthermal and thermal (thermal fluctuation)-it is concluded that the latter is the more important. A comparison is made of the fluctuation theory of polymer strength with new experimental data on polymethyl methacrylate, and the causes of the transition from brittle to nonbrittle fracture are discussed. The effect of molecular orientation on the strength of polymers is examined on the basis of the fluctuation theory of strength.Mekhanika Polimerov, Vol. 2, No. 5, pp. 700–721, 1966     

Consideration of nonelastic losses in the determination of rigidity parameters of anisotropic polymers by ultrasonic methods

The propagation of oscillations in an orthogonally anisotropic medium with losses is investigated, using Hooke's law with complex coefficients. Functions are derived relating the complex modules of an orthotropic body to the parameters of propagation of ultrasonic oscillations. The effect of nonelastic anisotropy on the mechanical properties of the material is investigated. Equations are derived for the transition from complex modules to complex technical characteristics.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 32–38, January–February, 1972.     

Fatigue of a glass-fiber-reinforced plastic under sonic-frequency vibrations

A procedure is described for fatigue tests of glass-fiber-reinforced plastics specimens under conditions of symmetrical extension and compression with a steady peak of dynamic stress at a vibration frequency of approximately 500 Hz. As a test for fatigue failure we chose the steep increase in the mechanical loss angle of the vibrating system which occurs when a macrocrack is formed in the specimen. The time dependence has been plotted for the mechanical loss angle, the resonance frequency of the vibrations system, a parameter proportional to the peak deformation of the specimen, and the temperature of vibrational heating-up in its cross section where there is the greatest stress. The progress of these dependences has been analyzed in the build-up of fatigue damage in the material. An experimental relation has been obtained between the resultant dissipative function of the material and the peak dynamic stress. Results are given of fatigue tests on specimens of a glass-reinforced plastic winding cut in the weft direction of the reinforcing fabric.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1039–1043, November–December, 1972.     

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.     

Comparison of the mass spectra of the volatile products liberated from polymers in the course of mechanical destruction and thermal degradation

The compositions of the volatile products liberated from polymers in the course of mechanical destruction and thermal degradation have been studied and compared by means of mass spectrometry. For those polymers in which in both cases breakdown of the macromolecules begins with the basic chain, the volatile products are the same. For polymers in which breakdown of the molecules in thermal degradation begins with the stripping of side groups, the volatile products of thermal and mechanical degradation are different. This confirms and extends the ideas of the kinetic theory of fracture concerning the relationship between the processes of mechanical fracture and thermal degradation of polymers.Mekhanika Polimerov, Vol. 3, No. 1, pp. 80–88, 1967     

Design of Steel-Composite Multirim Cylindrical Flywheels Manufactured by Winding with High Tensioning and <Emphasis Type="Italic">in situ</Emphasis> Curing. 1. Basic Relations

The possibility of using force winding coupled with in situ curing to increase the energy storage capacity of hybrid steel-composite cylindrical flywheels is estimated and analyzed. Relations describing the rotational, thermal, and winding stresses are considered and discussed. These relations are used for a numerical analysis of the stress state and energy capacity of hybrid flywheels in the second part of the paper.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 203–224, March–April, 2005.     

Nature and mechanism of friction of rubberlike polymers in different physical states

We have investigated the frictional properties of crosslinked butadiene-nitrile and butadiene-styrene copolymers and natural rubber in friction against polished steel under vacuum conditions in the temperature interval from –200 to +150° C, which embraces the glassy and high-elastic states, as well as the transition region between them. The temperature dependence of polymer friction is characterized by two maxima, a principal and a low-temperature maximum. The principal maximum, observed in the glass transition region, is not associated with the mechanical loss maximum observed in the polymers themselves. The temperature dependence of the force of friction is composed of three parts. In the high-elastic region there is an increase in the force of friction with fall in temperature, in accordance with the molecular-kinetic theory of friction of rubberlike polymers. In this region the nature of friction is associated with mechanical losses in the surface layer of polymer. The mechanical losses inside the polymer itself are unimportant. The deviation from the theoretical curve and the fall in the force of friction below a certain temperature in the transition region are chiefly associated with a decrease in the actual area of contact as the polymer passes into the glassy state. In the glassy region the friction is significantly determined by the mechanical losses in the polymer itself associated with the repeated elastic and forced-elastic deformation of the asperities in the layer of polymer in contact with the rigid surface. Therefore the low-temperature maximum is closely related to the mechanical loss maximum observed in the same temperature region in dynamic tests. Apart from this, the friction maximum is also associated with the increase in the forces of adhesion and the reduction of the actual area of contact at temperatures at which a forced-elastic mechanism of compression of the polymer asperities is not realized.Mekhanika Polimerov, Vol. 3, No. 1, pp. 123–135, 1967