Vibrocreep of polymer materials

The normal and vibrational creep and recovery of low- and high-density polyethylene (LDPE and HDPE) and filled LDPE have been studied experimentally under isothermal conditions when the superposition of vibration is not accompanied by mechanohysteresis heating of the material.Mekhanika Polimerov, Vol. 4, No. 2, pp. 246–254, 1968     

Static and vibrational creep of a fabric-reinforced plastic in shear in the plane of the reinforcement

The results of a comparative experimental investigation of the short-term static and vibrational creep of a fabric-reinforced plastic in shear in the plane of the reinforcement are presented. The experimental procedure is described in detail. It is shown that on the investigated ranges of temperature, stress, and amplitude-frequency parameters the effect of an additional vibrational load on the creep process is unimportant.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 605–610, July–August, 1971.     

Vibrational creep of polymeric materials

An experimental study of the effect of vibration on the creep process has been carried out in the case of the rigid porous polyurethane PPU-3, as a function of the magnitude of the vibrational loading and the level of basic static stresses. It has been shown that with increase in the velocity amplitude of the dynamic stresses, the creep process is accelerated, without being accompanied thereupon by vibrational heating of the material. The possibility has been established of approximating vibrational creep curves by the integral equation of Volterra, using a discrete series of relaxation times transformed by the vibro-time analogy method.For Communication No. 3, see [1].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 223–232, March–April, 1970.     

Flow characteristics of a metasilicate-filled low-density polyethylene melt

Certain of the flow characteristics of a filled low-density polyethylene melt have been investigated. The results obtained are compared with the results of measurements in the single-frequency vibrational shear regime.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 693–697, July–August, 1969.     

Effect of loading on the vibrations of the molecules of certain polymers with a plane zigzag skeleton

The main-chain vibrational frequency shifts are calculated on the basis of a simplified model for a series of loaded polymers with a plane zigzag skeleton. The dispersion curves and distribution functions for the free and loaded molecules are compared.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 971–978, November–December, 1970.     

Vibrocreep of polymeric materials

Experimental data on the static and vibrational creep of rigid porous polyurethane are used in an analysis of the time dependence of the vibrocreep coefficient and its dependence on the derivative of the stresses created by the incremental vibrational load and the static stress level. It is shown that at a constant value of the static stresses and the incremental vibrational load the vibrocreep coefficient decreases with time and in long-time vibrocreep tends to unity. As the parameter characterizing the vibrocreep coefficient for a given moment of time it is possible to employ the amplitude of the dynamic stress rate. The dependence proposed for describing the vibrocreep coefficient curves satisfactorily describes the experimental data. It is shown that the value of the vibrocreep coefficient does not depend on the static stress level (up to 0.5 of the short-time strength).For Communication 5, see [9].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 643–647, July–August, 1970.     

An asymptotic calculation of the vibrations of a viscoelastic cylinder with a slowly varying internal boundary

The vibrational problem is considered for a long hollow viscoelastic cylinder with a variable internal boundary, this being enclosed in an elastic shell. An asymptotic method based on averaging is used to find the resonant vibrations in response to a small uniformly distributed internal pressure that varies periodically with time. The calculation is carried through to quadrature working formulas.Moscow Institute of Electric Machine Construction. Translated from Mekhanika Polimerov, No. 5, pp. 935–939, September–October, 1973.     

An investigation of the dynamical mechanical properties of some block polymers using the resonant vibration method

Some results are presented, obtained on the RUIZ-2T apparatus, for the determination of the decrement and characteristic vibrational frequencies of polymer samples by the resonance method.V. I. Lenin Moscow State Pedagogical Institute, Problem Laboratory for the Physics of Polymers. Rostov-on-Don Institute for Railway Transport Engineers. Translated from Mekhanika Polimerov, No. 1, pp. 152–154, January–February, 1972.     

The half-widths of the bands due to the skeletal vibrations of polyethylene molecules,free and under an applied load

The third-order phonon interactions in free polyethylene chains and polyethylene chains under load have been analyzed to obtain the theoretical temperature dependence of the half-widths of the bands due to the skeletal vibrations potentially active in the absorption and Raman spectra. The problems of the harmonic and anharmonic vibrational analysis of polymers under load are discussed.A. F. Ioffe Order of Lenin Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 3–11, January–February, 1972.     

Applicability of the superposition principle to periodically loaded polyethylene

The lifetime of isotropic specimens of high-density polyethylene subjected to periodic tensile loading and "recovery" has been investigated. The lifetime determined without allowance for the time for "recovery" of the polymer is greater than the lifetime under constant load; under periodic application of a constant stress the lifetime increases exponentially with increase in the length of the "recovery" interval; at the same "recovery" time the life-time decreases exponentially with increase in the time under load during each cycle.Higher Chemical Engineering Institute, Sofia. Translated from Mekhanika Polimerov, No. 6, pp. 1009–1013, November–December, 1970.     

Nondestructive investigation of the thixotropic recovery of unvulcanized heavily filled rubber

A dynamic method has been used to estimate the thixotropic change in the viscoelastic properties of materials. The thixotropic recovery of the structure of a heavily filled rubber, destroyed by processing under stationary conditions, has been investigated. It is found that the relaxation spectrum changes during the recovery process.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 561–564, May–June, 1969.     

Nonlinear creep of TS8/3-250 glass-reinforced plastic

The creep and recovery of a glass-reinforced plastic are investigated within the frame-work of a nonlinear hereditary model. The material characteristics are determined for the three principal directions. The proportionality of the kernels is established.State Scientific-Research Institute of Machine Science, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 391–397, May–June, 1971.     

Elastic recovery of filled rubber mixtures after extrusion through round ducts

The results of an experimental study on the elastic recovery of filaments of filled rubber mixtures extruded through round ducts of various length are discussed. An empirical relationship which permits the effect of elastic recovery of filaments of a rubber mixture after extrusion from a round duct to be estimated as a function of the relative duct length has been established from the data measured.All-Union Scientific-Research and Technological Design Institute of the Rubber Industry, Volzhskii. Translated from Mekhanika Polimerov, No. 2, pp. 364–268, March–April, 1975.     

Lifetime of amorphous polymers under intermittent loading

The lifetimes of two types of amorphous polymers (polyvinyl chloride and plasticized epoxy resin) under intermittent loading have been investigated. It is established that the lifetime, determined without allowance for recovery time, is less than that under constant load. Under periodic loading at constant stress the lifetime varies with the loading regime. For each of the investigated polymers a lifetime minimum is observed at a certain duration of the loading and recovery periods.Higher Chemical Technology Institute, Sofia. Translated from Mikhanika Polimerov, No. 5, pp. 912–916, September–October, 1971.     

Hereditary theory of creep and low-cycle fatigue of polymeric materials

The results of an investigation of the creep of polymethyl methacrylate under alternating loading and recovery are presented. The experiments ended in the failure of the specimen. The creep data obtained are described on the basis of the nonlinear Boltzmann-Persoz theory and Bryzgalin's theory of hereditary recovery. Korabel'nikov's result, according to which for alternating loading and recovery the total time under load up to failure is less than the static life of the polymer, is confirmed.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow; Scientific-Research Institute of Mechanics, Lomonosov Moscow State University. Translated from Mekhanika Polimerov, No. 4, pp. 615–621, July–August, 1970.     

Dependence of the viscoelastic properties of polymer melts on filler concentration,frequency, and vibrational shear gradient

The properties of high-pressure polyethylene have been investigated at three filler concentrations and a temperatured of 130° C. There is a viscoelasticity limit with respect to vibrational shear gradient, above which a thixotropic reduction of the shear modulus and dynamic viscosity is observed. On the basis of the experimental data the dependence of the dynamic viscosity on shear gradient at various frequencies and filler concentrations is reduced to one invariant form.Mekhanika Polimerov, Vol. 4, No. 3, pp. 515–522, 1968     

Variation of the elasticoviscous characteristics of a heavily filled rubber after periodic shear deformation

The results of an investigation of the recovery of the elasticoviscous characteristics after thixotropic reduction by periodic deformation in the nonlinear zone are reported. The rate of recovery of the mechanical properties depends on the deformation frequency and the previous history of dynamic deformation is shown to affect the dependence of the elasticoviscous characteristics on the shear rate gradient. The effects of stationary and dynamic deformation regimes on the relaxation spectrum of the material are compared.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 528–533, 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.     

A matrix algorithm for computing the coefficients of the transformation of waves on a reinforcing rib

In the work a matrix algorithm is proposed for computing the transformation coefficients (the coefficients of reflection, transmission, and transformation into waves of other types) for any vector fields and any angles of incidence. The method is illustrated by computing the transformation coefficients of vibrational waves on a rectilinear reinforcing rib reinforcing a plate and an annular rib reinforcing a thin, cylindrical shell.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 89, pp. 134–151, 1979.     

Variation of the instantaneous modulus of elasticity of certain types of plastics under long-time static loads

The variation of the elastic characteristics of polymeric materials tested to destruction under long-time static loads has been investigated. Experiments on polymethyl methacrylate, KAST-V glass laminate, and Soviet and Finnish polyester glass-reinforced plastics under constant and intermittent (with "recovery") static tensile loads have shown that their elastic characteristics vary with the loading regime, the type of material, and the stress level. In a number of cases the value of the modulus of elasticity falls by 25–35%. This is attributed to the reduction of the effective cross section of the specimen as a result of damage accumulation.All-Union Correspondence Structural Engineering Institute, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 430–435, May–June, 1971.