Physico-mechanical properties of polymer materials and the friction problem

Aspects of the friction behavior of polymer materials associated with their molecular structure and responsible for the relatively small value of the modulus of elasticity as compared with the ultimate strength are examined. It is shown that, in view of the important influence of hydrostatic pressure on the mechanical properties of polymer materials, the mechanical characteristics obtained from uniaxial testing cannot be used in calculating the contact area and the forces of friction. Formulas are presented for calculating the mechanical characteristics under these conditions. The results of indentation experiments designed to simulate contact processes are discussed. It is shown that the resistance to deformation of the asperities on the surface of polymer materials is of the order of the yield stress, and not two or three times greater, as with metals. The results of contact creep studies are described and evaluated. The results of investigations of the mechanical and antifriction properties of filled polymer materials show that the forces of friction are inversely proportional to the modulus of elasticity, while the thermophysical characteristics are a function not only of the thermophysical characteristics of the filler and the base, but also depend to a great extent on the shape of the filler particles; thus, when a fibrous filler with a low coefficient of linear expansion is used, the thermal stability of the friction material can be considerably improved. The results of a study of the adhesion interaction of polymer materials under conditions of omnidirectional nonuniform compression and simultaneous deformation are presented. It is shown that the adhesion interaction is strong even at room temperature. Aspects of the mechanical properties of lubricants that determine their effectiveness in polymer friction are considered.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 303–314, March–April, 1969.     

On the theory of infrared dichroism of oriented amorphous polymers

A network model of a linear amorphous polymer is used as a basis for calculating the infrared dichroism of uniaxially and biaxially oriented material. The dependence of the dichroism on the uniaxial and biaxial stretch ratios, orientation temperature, and certain other factors is investigated. Previously published experimental data are discussed.Moscow Lenin State Pedagogical Institute, Problem Laboratory of Polymer Physics. Translated from Mekhanika Polimerov, No. 6, pp. 979–984, November–December, 1970.     

Interaction of a polymer matrix and short reinforcing fibers

A model of a glass-reinforced plastic with short unidirectional fibers is proposed. The distribution of tensile stresses in the polymer matrix and the fibers and the shear stress distribution at the interface in uniaxial tension are investigated in the elastic formulation.Riga Polytechnic Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1030–1035, November–December, 1971.     

Dynamic compressive strength of epoxy composites

The strength of laminated and unidirectionally reinforced composite materials was investigated in conditions of dynamic uniaxial compression with a strain rate of 50–1000 sec^–1 using the split Hopkinson pressure bar method. It was shown that in conditions of dynamic compression, glass/epoxy, aramid/epoxy, and carbon/epoxy composites exhibit elastic-brittle behavior with anisotropy of the strength and elastic properties. The effect of the strain rate on the strength characteristics of fiberglass-reinforced plastics was demonstrated.Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 6, pp. 776–782, November–December, 1995.Presented at the Ninth International Conference on the Mechanics of Composite Materials (Riga, October, 1995).     

Behavior of copolymers of styrene with polyester-acrylate in isothermal uniaxial compression

The behavior of a series of three-dimensional copolymers of styrene with polyester-acrylate has been investigated in isothermal uniaxial compression and recuperation. The similarity of the behavior of linear and three-dimensional polymers is noted. It is shown that the behavior of polymer specimens in repeat compression after a recuperation period is determined by the relaxational nature of the recuperation process. A relation has been established between the forced-elastic limit in compression and the structure of certain three-dimensional polymers. The effect of the concentration of initiating system components on the forced-elastic limit in compression is demonstrated.Mekhanika Polimerov, Vol. 3, No. 2, pp. 195–199, 1967     

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.     

Automation system for investigating the viscoelastic properties of biomaterials with a low elastic modulus

Conclusions The automation system makes it possible to investigate the viscoelastic properties of biomaterials with a low elastic modulus in a model medium under prescribed loads and to study their relaxation characteristics under uniaxial tension.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 884–888, September–October, 1983.     

Investigation of the deformation of a rubbery network polymer (SKN-40) in various types of states of stress

From the experimental data on equilibrium uniaxial and nonsymmetrical and symmetrical biaxial tension and pure and mixed shear it follows that the deformation behavior of SKN-40 crosslinked butadiene-nitrile copolymer is more accurately described by the Bartenev-Khazanovich high-elastic potential. The potential of the classical statistical theory of high elasticity of network polymers does not describe different types of states of stress with the same value of the material constant.Lenin Moscow State Pedagogical Institute, Laboratory for Problems in Polymer Physics. Leningrad Branch of the Scientific-Research Institute of the Rubber Industry. Translated from Mekhanika Polimerov, No. 5, pp. 840–845, September–October, 1971.     

Problems of the dynamic behavior of blood vessels as shells

Problems of the dynamic behavior of blood vessels as deformable shells with a viscous fluid flowing in them are investigated. A multicoat elastic shell in which an active (muscular) coat is distinguished is proposed as a model of the vessel. Problems that can be solved on the basis of the model are discussed.N. E. Zhukovskii Military-Air Academy. Translated from Mekhanika Polimerov, No. 2, pp. 373–379, March–April, 1970.     

Deformation criterion of the strength of plastics in biaxial compression

The deformation at break under uniaxial loading is taken as a criterion of the strength of an anisotropic glass-reinforced plastic in biaxial compression. Formulas are obtained for determining the breaking stresses and their limits of applicability are investigated. The calculated values of the breaking stresses are in agreement with the experimental values for both instantaneous and long-term loading.Mekhanika Polimerov, Vol. 4, No. 2, pp. 276–281, 1968     

Mechanical properties of glass fabric-reinforced plastics in tension and compression normal to the plane of reinforcement

The behavior of glass-reinforced plastic based on ASTT (b)S₂-O fabric and NPS-609-21M resin in tension and compression normal to the plane of reinforcement has been investigated and the mechanical characteristics determined. Recommended values are given for the size and shape of the test pieces, and a method of determining the tensile and compressive characteristics of glass-reinforced plastics is proposed.Leningrad. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 803–809, September–October, 1968.     

Asymptotic behavior of an SEI epidemic model with diffusion

An SEI epidemic model with constant recruitment and infectious force in the latent period is investigated. This model describes the transmission of diseases such as SARS. The behavior of positive solutions to a reaction–diffusion system with homogeneous Neumann boundary conditions are investigated. Sufficient conditions for the local and global asymptotical stability are given by linearization and by the method of upper and lower solutions and its associated monotone iterations. Our result shows that the disease-free equilibrium is globally asymptotically stable if the contact rate is small.     

Experiments and numerical simulations on damage behavior of biaxially loaded specimen

The paper deals with the effect of stress state on damage and failure behavior of isotropic ductile metals. In the continuum damage model the damage behavior of ductile metals is adequately described by a generalized damage condition and an anisotropic damage rule. The damage criterion is based on series of uniaxial experiments with differently notched specimens and corresponding numerical simulations as well as on various numerical calculations on the micro-scale. Different branches of the damage criterion depending on stress triaxiality and Lode parameter are considered. To be able to validate the proposed stress-state-dependent functions new experiments with two-dimensionally loaded specimens have been developed. Corresponding numerical simulations show that these shear-tension and shear-compression tests cover a wide range of stress triaxialities and Lode parameters. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

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.     

Deformation behavior of a filled nitrile vulcanizate in various states of stress

On the basis of experimental data obtained in uniaxial and symmetrical and nonsymmetrical biaxial tension and pure shear, the deformation behavior of unfilled and filled butadiene-nitrile rubbers is described by means of the Bartenev-Khazanovich one-parameter high-elastic potential.Leningrad Branch of the Scientific-Research Institute of the Rubber Industry. Translated from Mekhanika Polimerov, No. 2, pp. 363–366, March–April, 1972.     

A rheological model of polymers and glass-reinforced plastics

Network polymers and the corresponding glass-reinforced plastics are investigated for a homogeneous uniaxial state of stress and constant temperature. A physical law relating the high-elastic strain and the stress in explicit form with once-determined structural constants is obtained for the damped (bounded) creep regime. The theoretical solutions are compared with the experimental data for a glass-reinforced plastic based on unsaturated polyester resin and glass mat reinforcement.Institute of Engineering Mechanics, Bulgarian Academy of Sciences, Sofia. Translated from Mekhanika Polimerov, No. 5, pp. 851–857, September–October, 1971.     

A multi-structured single-product dynamical model

We consider a single-product dynamical model with funds of different structures. The asymptotic behavior of the structure function and of the spectral distribution function for the work on the funds are investigated. There are three references.Translated from Matematicheskie Zametki, Vol. 11, No. 3, pp. 307–312, March, 1972.     

Changes in the mechanical properties of polycarbonate produced by a powerful light flux

The effects of a laser beam on PC are examined in relation to the power and duration of the light pulse. In uniaxial tension there is a sharp change in the relative elongation of the irradiated specimens (pulse length 10^–3 sec); the elastic modulus and the molecular weight remain unchanged. Irradiation of PC with a giant pulse does not affect its mechanical properties.Mekhanika Polimerov, Vol. 4, No. 2, pp. 288–292, 1968