Effect of ultraviolet radiation on the creep rate of polymers

The effect of UV radiation on the creep rate of nine different polymers has been determined under load. A reversible increase in creep rate has been detected. This effect is attributable to radiation damage consisting in the breakage of bonds in the stressed polymer. The results obtained point to a close relationship between the processes of polymer fracture and deformation.Mekhanika Polimerov, Vol. 3, No. 3, pp. 404–408, 1967     

Molecular mechanism of oriented crystalline polymers

It is shown with reference to linear polyethylene that the deformation of an oriented crystalline polymer takes place as a result of elongation of the coiled parts of the macromolecules in the amorphous zones owing to conversion of gauche into extended trans isomers. The decrease in coiled isomer content when the specimen is deformed by approximately 5% is accompanied by a small number of chemical bond breakages. Repeat deformation by the same amount does not result in any additional breakage of polymer chains.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of The USSR, Leningrad. Translated from Mekhanika Polimerov, No. 4, pp. 584–588, July–August, 1973.     

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     

Effect of residual stresses on the strength of oriented glass-reinforced plastics

The effect of structural residual stresses on the strength of a glass-reinforced plastic loaded along and across the fibers is investigated. It is established that the residual stresses lead to an increase in the strength of the glass-reinforced plastic across the fibers and to cracking of the polymer matrix in tension along the fibers, but have practically no effect on the combined deformation of the matrix and the fibers in compression.Moscow Ordzhonikidze Aviation Institute. Translated from Mekhanika Polimerov, No. 3, pp. 475–480, May–June, 1969.     

Deformation of polymer materials in nonuniform omnidirectional compression

The author presents the results of experiments to determine the nature of the deformation of 12 polymer materials compressed in thick-walled metal tubes. It is shown that there is a considerable increase in the plasticity of the materials. Moreover, it has been found that all the materials are capable of adhesion when two specimens are deformed together. However, for most of the materials tested the strength declines with increase in strain owing to cracking.Mekhanika Polimerov, Vol. 2, No. 2, pp. 229–233, 1966     

Control of biopolymer poly-β-hydroxybutyrate characteristics by γ-irradiation

The influence of γ-irradiation on the structure and some mechanical properties of poly-β-hydroxybutyrate was studied. Specimens of PHB were γ-irradiated with various doses (1–20 Mrad) in air and vacuum. The molecular weight, structural characteristics of the crystalline and amorphous phases, characteristics of thermal degradation, and deformation of the polymer were determined. The crystallinity was found to increase with increase in the radiation dose and with the corresponding reduction in molecular weight. The increase of crystallinity was the greater the smaller the length of macromolecules (higher radiation dose). The melting temperature T _m , which characterizes the crystalline order, decreased with decrease in the molecular weight. The results of calorimetric studies suggest that radiation-caused degradation, which occurs at a temperature at which “cold” crystallization (60°C) is possible, might also affect the crystalline part of the polymer.     

Effect of the physical state on tearing of amorphous polymers

The temperature dependence of the basic tear characteristics of deformation and failure of SKS-85 copolymer in the range from Tg to T>T_f is examined. It is established that the total work done in tearing the polymer in the brittle state is determined by the work of deformation up to separation of the specimen into two parts. In contrast to this, the total work done in tearing the polymer in the high-elastic state is determined mainly by the work of formation of the tear surface.Mekhanika Polimerov, Vol. 1, No. 5, pp. 71–77, 1965     

Thermomechanical properties of spot-bonded nonwoven synthetic-fiber materials

The thermomechanical properties of spot-bonded nonwoven synthetic-fiber materials with a polymer binder have been investigated. The materials are composed of heterogeneous fibers, with low-melting polymers (binder) forming the surface layer. The change of deformation in uniaxial tension was studied from 20 to 150° C (rate of temperature increase 1.5° C/min) as a function of the nature of the fibers and the binder, their relative proportions, and the density and weight of the material. A theoretical explanation of the observed effects is offered.Mekhanika Polimerov, Vol. 4, No. 2, pp. 300–303, 1968     

Plastic deformation of models of a crystalline polymer with increased lattice defectivity

Conclusions 1. On the basis of two-dimensional models, the structure of a polymeric crystal containing more than one lattice defect has been determined on an electronic computer. The types of defects are: a) double vacancy, model I; b) two isolated vacancies, model II; c) a combination of isolated vacancies and double vacancies, model III. Plastic deformation curves have been calculated for all three models.2. It has been observed that increase in the degree of defectivity in a crystalline polymer significantly reduces the elastic limit and reduces the strength limit of the structure very little. The elastic limit falls particularly strongly with increase of the defectivity in a state of hydrostatic stress.3. Increase in the density of crystallographic defects causes significant mutual rearrangement of the coordination polygons of the crystal lattice, which occurs as the result of plastic deformation.Report presented at the Third All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1976.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 397–402, May–June, 1977.     

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.     

Effect of physicalstate on tearing of filled systems based on linear amorphous polymers

A study has been made of the temperature dependence of the service behavior, deformation, and tear rate of filled systems based on SKS-85. It is established that the introduction of fillers which enhance the strength of systems in the high-elastic state effect a loss of strength in the vitreous state. The observed reversal of the strengthening effect from positive to negative is explained by weakening of the adhesive strength of the bond between polymer and filler particles caused by the increase and concentration of shrinkage stresses during cooling of the specimens. This effect is called temperature inversion of the reinforcing action of fillers.Mekhanika Polimerov, Vol. 1, No. 6, pp. 98–102, 1965     

On the deformation of an extended viscoelastic rod subject to finite deformations

The deformation of a polymer material subjected to tensile strain is considered with due allowance for physically linear creep at finite deformations. The deformation process is only stable in time up to a certain value of the load; under heavier loads the deformation is unstable. An expression is derived for the critical time.Institute of the Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1130–1133, November–December, 1972.     

Strength and deformability of reinforced polymers in tension normal to the fibers

The strength and deformability of reinforced polymers in tension across the fibers is investigated. It is assumed that the polymer deforms as an ideal elastoplastic body. Relations are obtained for the nature of the deformation of the polymer between the fibers and the strength and deformability of the composite with allowance for the structural distribution of the components. Theoretical stress-strain diagrams are presented for composites with different reinforcement densities and resin elasticities. The theoretical values of the strength and deformation of reinforced polymers with the load applied across the fibers are compared with the results of experiments on model specimens of epoxy-Thiokol polymers.Leningrad Mechanical Institute. Translated from Mekhanika Polimerov, No. 4, pp. 682–687, July–August, 1970.     

Effect of liquid media on the deformation of the surface layers of a polymer-metal pair in sliding friction

The relation between the high-elastic component of polyurethane deformation and the deformation of the surface layers of metals has been investigated for sliding friction in various media. The surface layers of polymer and metal are plastically deformed. There is a certain correlation between the coefficient of friction and the amount of deformation.Kiev Institute of Civil Aviation Engineers. Translated from Mekhanika Polimerov, No. 1, pp. 147–149, January–February, 1970.     

Micromechanics of polymer fracture

Small-angle x-ray scattering has been used to investigate the formation of embryonic submicroscopic cracks in polymers under a load. The main characteristics of crack formation in various loading regimes are analyzed. It is shown that there is a relation between the submicrocrack concentration and the deformation of the loaded polymer. The principal parameters of crack formation determining the strength properties of the polymer are found to be the transverse dimension of the initial submicrocracks relative to the loading axis, which is determined by the structural heterogeneity of the material, and the submicrocrack concentration in the prefracture state. The principles of the micromechanics of polymer fracture are formulated on the basis of the results of an analysis of the quantitative relationship between these parameters. The dominant role of the surface in the fracture process is demonstrated by comparing the parameters of crack formation in the interior and at the surface of the loaded polymer.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 792–801, September–October, 1974.     

Development of slits in polyethylene and polypropylene films stressed in uniaxial tension

Optical microscopy has been used to investigate the development of a slit in polyethylene and polypropylene films with spherulites of different types and sizes stressed in uniaxial tension. The angle between the slit and the direction of extension was 0, 45, or 90°. Slits at 45 and 90° initially develop through localization of slits by a stronger oriented polymer and subsequently as a result of failure of the oriented polymer at the tip of the slit. A longitudinal slit does not develop and does not affect the deformation of the film.Mekhanika Polimerov, Vol. 3, No. 1, pp. 95–98, 1967     

The role of the porous structure of the filler in the reinfo rcement of polymers

Composites consisting of polyethylene and porous fillers with various pore sizes (from 22 to 115 Å) and surface types have been investigated. It is shown that the polymer filling the pores takes part in the deformation processes. The modulus of elasticity of the filled polymers is directly proportional to the filler surface per gram polymer. It is proposed to characterize the activity of the fillers by reference to the slope of the straight lines E-S with the hydrodynamic effect excluded.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 253–258, March–April, 1973.     

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.     

Relation between the strength of polyethylene-steel adhesion bonds and the thickness of the ultrathin layer of polymer remaining on the surface of the metal

On the basis of the principle of ellipsometry and, moreover, the method of pyrolitic decomposition of the polymer with subsequent chromatographic analysis of the products of pyrolysis, a procedure has been developed for experimentally determining the thickness of the ultrathin layer of polymer that remains on the metal after failure of a polyethylene-steel adhesion bond. The nature of the relationship between the thickness of the residual polymer layer (200–800 Å) and the strength of the adhesion bond is established. It is concluded that the cohesion strength and the deformation at failure of the layer of adhesive next to the more rigid and stronger boundary layer have a decisive influence on the strength of the adhesion bond.Riga Polytechnic Institute. Translated from Mekhanika Polimerov, No. 3, pp. 420–424, May–June, 1976.     

Locomotion based on the control of the shape of magnetic fluid surfaces and of magnetizable media

The realization of locomotion based on the deformation of a free surface of a magnetic fluid layer in a traveling magnetic field is studied. A plane flow of an incompressible viscous magnetic fluid layer on a horizontal surface in a nonuniform magnetic field and a plane two-layers flow of incompressible viscous magnetic fluids between two parallel solid planes in a magnetic field is considered. Also the flow of an incompressible viscous magnetic fluid layer on a cylinder in a nonuniform magnetic field is an object of investigation. The deformation and the motion of a body made by a magnetizable polymer in an alternating magnetic field are experimentally studied. The cylindrical body (worm) which is located in a cylindrical tube is analyzed. These effects can be used in designing autonomous mobile robots without a hard cover. Such robots can be employed in clinical practice and biological investigations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)