Characteristics of the creep and repeat creep deformation process for polymers in uniaxial tension. Part 2

Physical relations for approximating the creep deformation and recovery have been worked out for a material in the physically nonlinear state with a nonmonotonic θ (t) dependence. It has been shown experimentally that for filled low-density polyethylene and fluoroplastic there is no time similarity for the processes of longitudinal and transverse deformation, deformation under primary and repeat loading, and creep deformation and recovery.     

Characteristic features of the deformation process on creep and secondary creep of polymers under conditions of monaxial tensioning. Part I

Experiments carried out in the field of linear and nonlinear creep of a filled polyethylene and Teflon resin, including two complete cycles of creep and deformation recovery at monaxial tensioning, show that the bulk deformations (t) change nonmonotonically, and relationships computed by summation of terms containing a function of time cannot be used to approximate the deformation.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 399–405, May–June, 1974.     

An analytical description of the creep behavior of polymers in a flowing state in the linear deformation region

The methods available for the estimation of the parameters, which determine the steady state conditions for the slow shear flow of polymers, under indifferent creep conditions have been considered, and the results of experiments carried out using a shear plastometer have been compared with calculations in which Boltzmann-Volterra equations with a memory characteristic have been used. The resolvent previously suggested in [3] has been employed in these latter equations. It has been shown that the equilibrium values for the modulus of rubber-like elasticity can be calculated from the results of experiments on unsteady creep states.     

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.     

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.     

A molecular model of creep and stress relaxation in crystalline polymers

A possible model of defect formation in a polymer crystal lattice is considered. The results of an investigation of creep and stress relaxation in crystalline polymers are interpreted on the basis of the model proposed.T. G. Shevchenko Kiev State University. Translated from Mekhanika Polimerov, No. 6, pp. 969–975, November–December, 1971.     

Relation between fracture and deformation in oriented polymers

The development of submicroscopic cracking under load has been studied (by a small-angle X-ray scattering technique) in such oriented polymers as Kapron (Nylon 6), polypropylene, etc. The increase in crack density (N_cr) is compared with the variation of the tensile strain (). The observed correlation between and N_cr indicates that the processes of fracture and deformation of oriented polymers are closely connected. The presence of a similar correlation in loading-relaxation-repeat loading experiments establishes fracture as the primary process.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 43–47, January–February, 1970.     

Predicting the deformation properties of polymers

Physically well-founded relations, following from a consideration of the molecular-kinetic nature of the relaxation processes, are proposed for the time-temperature superposition principle. It is shown that the well-known Williams—Landel—Ferry relation is a particular case of more general formulas.V. I. Lenin Moscow State Pedagogical Institute, Problem Laboratory of Polymer Plastics. Translated from Mekhanika Polimerov, No. 6, pp. 1106–1109, November–December, 1971.     

Multiparametric prediction of the creep of polymer materials

The article discusses phenomenological methods for predicting long-term creep, using stress-, temperature-, and vibro-time analogies. Starting from several previously introduced hypotheses, the article proposes a generalized nonlinear thermo-vibro-rheological relationship in which the complex stress-, temperature-, and vibro-time dependences are reduced separately to a time dependence (with certain basic reference values of , T₀, and , chosen arbitrarily), and to dependences; the latter appears only in the change of the time factorsa (_i),a _T(T), and . The prediction methods have been verified experimentally.Institute for the Mechanics of Polymers, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 420–428, May–June, 1970.     

Study of the two-dimensional deformation of polymers

The effect of two-dimensional deformation on the mechanical properties of films made from the hydrochloride of polyisoprene rubber is studied. The laws determining the reversible deformation of films when _y=0 are investigated. The results obtained are discussed in relation to supramolecular structures in polymers.Mekhanika Polimerov, Vol. 1, No. 2, pp. 21–26, 1965     

Study of the two-dimensional deformation of polymers

The authors have investigated the effect of the degree of extension on the strength and shrinkage of polyisoprene chloride rubber film. It is shown that the breaking strength and shrinkage at elevated temperatures are determined only by the degree of extension in the corresponding direction and are almost independent of the extension in the other direction.Mekhanika Polimerov, Vol. 2, No. 3, pp. 350–354, 1966     

Acoustic measurements in rubberlike polymers during compressive deformation

Problems associated with the method of measurement of acoustical properties of viscoelastic materials and the influence of various external factors (temperature, pressure) on these materials have been examined. The results of measurements of propagation speeds and damping coefficients of waves of the sonic and ultrasonic regions in resins are given for discrete excitation frequencies and during simultaneous static action on the specimen. It is shown that uniaxial compression of the resin results in the appearance of dispersion of the dynamic elastic modulus. A possible explanation of this phenomenon is suggested.Dnepropetrovsk Civil Engineering Institute. Translated from Mekhanika Polimerov, No. 1, pp. 149–156, January–February, 1974.     

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     

High-frequency periodic deformation of polymers in the viscous-flow state

The propagation of high-frequency periodic vibrations in melts and solutions is considered in the case where the acoustic characteristics of the material are determined by the deformation amplitude. It is shown that in sufficiently large specimens the consequences of periodic deformation are concentrated near the vibration source, as a result of which a layer of material with strongly modified mechanical characteristics develops. It is suggested that when periodic high-frequency deformation is superimposed on steady-state flow, owing to the presence of a boundary layer there is effective slippages of the material at the vibration-emitting surfaces.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 722–728, July–August, 1973.     

Periodic axial and shear deformation of polymers in the viscous-flow state

Results are given of an experimental investigation of the combined periodic axial and shear deformation of polymers in the viscous-flow state. Specimens in the form of right cylinders were disposed between two parallel plates to which the material adhered completely. The experimental data are compared with those obtained under simple shear. The results indicate that, with combined periodic axial and shear deformation, nonlinear shear deformations affect the axial viscoelastic properties and nonlinear axial deformations affect the shear properties of the material.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 880–885, September–October, 1972.