Problems of the theory of deformation of polymeric materials under complex loading

Research on problems of the theory of deformation of polymeric materials under complex loading based on a synthesis of creep theories and the local strains theory is reviewed.Presented at the 2nd All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1971.M. V. Lomonosov Moscow State University. Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 434–443, May–June, 1972.     

Supermolecular structure and properties of polymers

Questions relating to methods of obtaining supermolecular structures and their effect on the properties of polymers are considered.Presented at 2nd All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1971.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 409–415, May–June, 1972.     

Some features of the frictional behavior of polymeric crystalline materials

The coefficients of friction for thin polymeric films are calculated, and it is shown that the coefficient of friction of the films is much less than that of a homogenous block. This may be due to some features of the antifriction properties of polymeric crystalline materials.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1053–1058, November–December, 1972.     

Nonlinear periodic deformation of thixotropic media

The experimental procedure and the processing of results on the nonlinear periodic deformation of polymeric and dispersed system melts are examined. Experimental data are given on the effect of the amplitude of harmonic deformation on nonlinear stress distortions.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 689–696, July–August, 1972.     

Polymer friction

The results of research on the antifriction properties of polymeric materials and expressions for calculating their coefficient of friction are presented. The effect of the mechanical properties of the materials on their antifriction characteristics is discussed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 421–429, May–June, 1975.     

Effect of hydrostatic pressure on certain thermodynamic properties of polymeric materials

By means of a thermodynamic approach it is demonstrated that the mechanical properties of homogenous polymeric materials depend only on specific volume. Expressions are derived for the entropy and volume coefficient of thermal expansion as functions of hydrostatic pressure and temperature. It is shown that for both crystalline and amorphous polymeric materials the bulk modulus depends on reduced temperature.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 825–829, September–October, 1970.     

Prediction of creep of polymeric materials during random processes of change in loading and temperature-humidity conditions of surrounding media

Conclusions 1. On the basis of the exponentialsmoothing method, a method is suggested for estimating the probability characteristics (statistical moments) of nonstationary random processes of change in temperature conditions of the surrounding medium.2. The possibility is shown of the application of the methods of theory of nonstationary random processes to the prediction of creep of polymeric materials which belong to the class of thermal—moisture rheologically simple solids during nonstationary random change in temperature and humidity of the material. The proposed method of prediction has been experimentally confirmed for the example of prolonged (27,000 h) creep of PN-3 polyester resin during simple shear under the climatic conditions of Riga.For Communication 1 see [1].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 616–621, July–August, 1976.     

Prediction of the creep of polyester resin in the presence of randomly acting temperature and humidity factors

The possibility of using the theory of random processes to predict the temperature and moisture creep of polymeric materials in the presence of randomly acting temperature and humidity factors is considered. A procedure for estimating the long-term deformation under such conditions is described with reference to the uniaxial creep of PN-3 polyester resin using time—temperature and time—moisture superposition. The possible correlation of the ambient temperature and humidity is taken into account. The results of a computer calculation show that the theoretical and experimental data are in satisfactory agreement.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 219–226, March–April, 1973.     

Strength of fibrous composites

Research on the effect of various factors on the strength of fibrous composites in tension, compression, shear, bending and plane stress, published in the journal Polymer Mechanics, is reviewed. The more important future trends are outlined.Presented at the 2nd All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1971.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 553–562, May–June, 1972.     

Influence of a plasticizer on the viscoelastic properties of polyvinyl chloride and the time-concentration analogy

Conclusions 1. The addition of plasticizer shifts the generalized pliability curves in the direction of shorter times. However, for corresponding states, the more highly plasticized composition has smaller values of pliability.Paper presented at the Third All-Union Conference on Polymer Mechanics in Riga, 1976.All-Union Scientific-Research Institute for the Use of Polymeric Materials in Reclamation and Water Management, Elgava. Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 861–865, September–October, 1977.     

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.     

Determination of the complex dielectric constant of polymeric materials from the polarization current

A method of determining the frequency dependence of the complex dielectric constant of polymeric materials from the polarization current is considered; the basic relations of the phenomenological theory of dielectric losses and permittivity, from which the dielectric dispersion of solid dielectrics can be calculated, are given. The region of application of the method is analyzed and the principal existing computation methods are examined.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 507–511, May–June, 1976.     

Modern trends in the development of fibrous composites

The two main trends in the development of high-modulus composites are considered. Improved methods of calculation sensitive to the effects associated with the weak shear and transverse characteristics are reviewed. It is shown that the disadvantages of composites with a traditional arrangement of the reinforcement can be overcome. The properties of boron- and carbon-reinforced plastics with a traditional reinforcement structure are described and compared with those of three-dimensionally structured materials with two- or three-strand reinforcing. Whiskerized fiber reinforcement is also considered. A program of further research on high-modulus composites is outlined.Presented at the 2nd All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1971.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 541–552, May–June, 1972.     

Investigation of the relation between the depth of penetration and indentation diameter in polymer hardness measurements

It has been experimentally demonstrated that for polymeric materials the area of the indentation should not be calculated from the depth of penetration of the spherical indenter, since this gives hardness values that are too low. It is shown that when the surface of a polymeric specimen is indented by a rigid ball, the effect of the spherical stress tensor on the yield point is important; the average stress on the contact area at the beginning for forced high-elastic deformation is close to the compressive yield stress of the polymeric material and considerably higher than its tensile yield stress.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 995–998, November–December, 1971.     

Polymeric pairs having a low coefficient of friction

Results are given from studies on sets of pairs which have a coefficient of friction below 0.1 at medium specific loads and low rates of relative slippage. It is shown that this may be accomplished by using materials with different chemical structures in the pair, for example, Teflon and low-density polyethylene, or a self-lubricating material, for example oil-impregnated modified wood in a pair with a polymeric counterbody.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 933–935, September–October, 1973.     

Multiparameter prediction of polymer creep

An investigation of the thermocreep of low-density polyethylene (LDP) and the vibrocreep of porous polyurethane (PPU) in complex states of stress has shown that multiparameter creep prediction based on the combined application of the time-stress, time-temperature, and time-vibration superposition principles can be used for rapid analysis of the nonlinear viscoelasticity and thermovibrocreep of polymeric materials under complex loading.For communication 1 see [1].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 416–420, May–June, 1971.     

Applicability of the hysteresis friction model for estimation of the degree of inelasticity of polymeric materials. I

Conclusions It has been established that the inclusion of the hysteresis friction model as an approximate method of taking into account the degree of inelasticity of polymeric materials is useful in many cases, and the investigations in this direction are promising in particular for the purpose of refining in this approximation those procedures of acoustical measurements which do not at present yet have a proper theoretical basis in the viscoelastic formulation of the problem.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 147–153, January–February, 1978.     

Construction of a phenomenological theory of fracture of anisotropic media

The theory of fracture proposed in [1] is extended to anisotropic media.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 634–644, July–August, 1971.     

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.     

Basis of the local strains theory (review 2)

The evolution of the local strains theory since 1965 is reviewed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 5, No. 1, pp. 22–29, January–February, 1969.