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.     

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.     

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.     

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.     

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.     

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.     

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.     

Physical relations for an orthotropic material in the local strains theory

Compressible and incompressible orthotropic materials are investigated. A method of constructing variants of the local strains theory describing the deformation properties of an orthotropic material is developed on the basis of the concept of an elastic potential.Institute of Polymer Mechanics, AS LatSSR, Riga. Translated from Mekhanika Polimerov, Vol. 4. No. 6, pp. 970–975, November–December, 1968.     

Resolvents of the theory of orthotropic shells with low shear stiffness in force-moments and stress functions

The problem of the theory of orthotropic layered shells with low shear stiffness is reformulated in force-moments and stress functions on the basis of new strain continuity relations constructed with allowance for transverse shears.Physicomechanical Institute, Academy of Sciences of the Ukrainian SSR, L'vov. Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 950–952, September–October, 1970.     

On the construction of a variant of the theory of fracture

A theory of long-time strength that takes into account the accumulation of damage in the material in different directions is used as a basis for obtaining isochronous fatigue strength curves in stress space for complex states of stress.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 648–653, July–August, 1970.     

Prediction of the deformation and fracture of polymeric materials

Research on the development of express methods of estimating the long-term deformation of polymeric materials based on the use of the time-temperature, time-stress, time-vibration, and time-moisture analogies (superposition) is briefly reviewed. Questions of the multiparameter prediction of the creep of plastics with parallel and serial application of the various analogies are considered. A program of further research is outlined. The possibility of predicting the fracture processes of polymeric composites and estimating the comparative strength of the products obtained from them on the basis of the acoustic emission and thermal radiation effects is demonstrated.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. 498–514, May–June, 1972.     

Periodic deformation and viscous flow of polymer melts and solutions (communication 1)

The principles of the theory of thixotropy are formulated. The basic relations are obtained for cases of periodic vibration superimposed on shear flow. The effect of stationary shear flow on the linear dynamic characteristics of an elastic liquid is investigated. The calculated values are compared with the experimental data.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 519–527, May–June, 1969.     

Model of viscoplasticity in the local strains theory

A model of viscoplasticity is proposed within the framework of the local strains theory. The proposed model, which applies to a small local area, takes into account the interaction of rheonomic and plastic strains, the Bauschinger effect, and recovery of the material after unloading.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1126–1128, November–December, 1969.     

Statistical interpretation of the temperature and stress shift factors

Expressions for the temperature and stress shift factors are derived on the basis of a statistical-probability treatment of the segmental motion of the macromolecules using the theory of energy level transitions. It is shown that in the general case the temperature shift factor should depend on stress, and the stress shift factor on temperature.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 528–531, May–June, 1976.     

Viscoelastic characteristics of filled modified polyethylene melts

The effect of modifying polyethylene with maleic acid on the viscoelastic characteristics of filled melts has been experimentally investigated.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 558–560, May–June, 1971.     

Analysis of the strength of glass-fiber-reinforced shells upon loss of stability

An algorithm is developed for calculating and analyzing the components of the stress tensor on the basis of an experimental function of deflections in the case of buckling of glass-fiber-reinforced shells loaded by a hydrostatic load. Possible sites of fracture of a shell are established qualitatively with the use of Malmeister's strength theory.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 666–673, July–August, 1972.     

Apparatus for fatigue testing glass-reinforced plastic specimens in symmetrical tension-compression at acoustic frequencies

The characteristics of an electromechanical apparatus for fatigue testing glass-reinforced plastic specimens in symmetrical tension-compression at loads up to 10–40 kN and acoustic frequencies on the interval 300–5000 Hz are described.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 525–528, May–June, 1972.     

Particular case of the deformation of a nine-atom model

The dependence of the tensile loading on the length of a nine-atom plane model is calculated. The shapes of the model in tension are determined.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 545–547, May–June, 1975.     

Yield surfaces in local strain theory

The initial yield surfaces for biaxial tension and combined tension and torsion are determined on the basis of the local strain theory. The limit surfaces of the resultant stress on a local plane in tension (torsion) are obtained. A plastic strain probability factor is introduced and its values are calculated for various loading paths.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 594–598, July–August, 1971.     

On the applicability of two-dimensional applied theories to problems of the stability of axially loaded cylindrical shells made of materials with low shear stiffness

The applicability of two-dimensional applied theories of the Kirchhoff-Love, Timoshenko, and Ambartsumyan types to problems of the stability of shells with low shear stiffness [1] is discussed. The critical loads given by these theories are compared with those recently obtained [6–8] by solving the problem of the stability of a cylindrical shell on the basis of general solutions [3, 4] of the three-dimensional linearized equations of the theory of elasticity [5].Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. L'vov Polytechnic Institute. Translated from Mekhanika Polimerov, No. 1, pp. 141–143, January–February, 1970.