Variant of statistical interpretation of the formation of viscoelastic deformations of polymers

A variant of a statistical probability interpretation of elementary micromechanisms of formation of viscoelastic deformations of polymers is examined with the aid of the concept of dissymmetric media and the dissymmetry coefficient. A new rheological relationship is obtained, a particular case of which is the known equation of a typical linear viscoelastic body. A method is given for determining the relaxation spectrum for different intensity functions figuring in the rheological relationships. The results of the calculation are compared with the experimental data, exemplified by the creep of polyamide P-68.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 392–396, May–June, 1973.     

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.     

Acoustic fatigue of polymer materials

Work on the development of experimental techniques and methods of testing materials under high-frequency cyclic loading are briefly reviewed. Certain aspects of the acoustic fatigue of polymer materials are examined. Future research trends are discussed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 5, No. 1, pp. 108–126, January–February, 1969.     

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.     

Thermocreep of polyethylene in the cyclic temperature regime

The shear creep and recovery of low-density polyethylene has been investigated in the constant and cyclic temperature regimes. It is shown that in the cyclic regime the relaxation processes are accelerated and the nonisothermal creep strains become progressively greater than the isothermal strains at the maximum temperature of the cycle. In recovery the relaxation spectra are shifted along the time scale relative to the creep spectra, the shifts for simple shear and uniaxial tension being nonidentical.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 227–235, March–April, 1969.