Creep of certain polymers under hydrostatic pressure

The problems of an experimental investigation of polymer creep under omnidirectional hydrostatic pressure are considered. The method of investigation is discussed, and the loading devices are described. The results of tests on low-pressure polyethylene and teflon are reported.Mekhanika Polimerov, Vol. 4, No. 2, pp. 232–236, 1968     

Creep of fluoroplastic under the joint action of tension and hydrostatic pressure

Conclusions 1. The effect of hydrostatic pressure on the creep of Teflon has been investigated under isothermal conditions. The applicability of the principle of reduced variables for reduction of creep curves with respect to pressure has been shown.2. It has been ascertained that in the pressure region from atmospheric to 1600 kgf/cm² there are two subregions, which are separated by a transition at a pressure of 700–800 kgf/cm². It has been shown that in these subregions the occurrence of relaxation processes has different characters.3. A direct measurement of the free volume of Teflon has been made in the temperature range from 40 to 120°C. A sharp increase in free volume in the region of the temperature transition has been shown.Leningrad Technological Institute of the Refrigeration Industry. Okhtinsk Scientific and Industrial Union "Plastpolimer," Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 434–438, May–June, 1977.     

Effect of hydrostatic pressure combined with uniaxial tension on certain physical properties of polymers

The residual changes in the density and swelling properties of high-density polyethylene, teflon, PVC, and ebonite after extension under hydrostatic pressure have been investigated. It is shown that in this case the density of all the materials tested is higher and the swelling lower than in the case of uniaxial tension alone. This effect of hydrostatic pressure is attributable to the creation of favorable conditions for the healing of cracks formed in the deformation process.Mekhanika Polimerov, Vol. 3, No. 6, pp. 1018–1023, 1967     

Creep of fluoroplastic in shear with application of hydrostatic pressure

Conclusions 1. It has been shown that under a deformation regime with Vxy = const, with an increase in shear deformation the effect of the action of hydrostatic pressure rises. A considerable effect of pressure on the character of the shear diagram is observed in the pressure region above 500 kgf/cm².Paper presented at the Third All-Union Conference on Polymer Mechanics in Riga, 1976.Leningrad Technological Institute of the Refrigeration Industry. Okhtinsk Scientific-Manufacturing Union Plastpolimer Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 812–818, September–October, 1977.     

Influence of hydrostatic pressure on the lifetimes of polymers

Under uniaxial tension, the lifetimes of polymers under hydrostatic pressure are longer than under atmospheric pressure. This effect is attributed to a change in the failure mechanism under pressure owing to retardation of the free-radical chain reaction of breakage of the macromolecules under omnidirectional compression.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 207–213, March–April, 1976.     

Creep of compact human bony tissue under tension

The behavior of compact bony tissue from a human tibia with time at various levels of a constant lengthwise stretching load has been studied. The limits of application of the linear viscoelastic theory for bony tissue have been established. Characteristics of the material have been determined which make it possible to describe both active and also retrograde creep.     

Creep of linear unoriented polymers in tension,compression, and torsion

The creep of polymethyl methacrylate, polystyrene, and polyethylene in tension, compression, and torsion has been investigated over a broad interval of temperature below the glass transition point. It is shown that the creep criterion changes depending on the temperature. This is associated with changes in molecular mobility.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 24–28, January–February, 1970.     

Effect of hydrostatic pressure on submicrocrack formation in oriented polymers

Small-angle x-ray scattering has been used to obtain a quantitative estimate of the concentration and size of the submicrocracks in Kapron and polypropylene equally extended at 1 and 1500 atm. Direct evidence of the retarding effect of pressure on fracture development has been obtained.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga: Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 917–921, September–October, 1971.     

Effect of hydrostatic pressure on the water absorption of epoxy polymers

The water absorption of epoxy polymers at hydrostatic pressures up to 1000 kgf/cm² has been studied. It has been shown that pressure very definitely reduces the water absorption value but essentially does not change the diffusion coefficient of water into the polymers under study. An explanation of the data obtained is given.     

The equilibrium of a flexible membrane under hydrostatic pressure

In the construction industry it is often necessary to drain a section of a canal. This may be done after the insertion of flexible membranes made of PVC‐coated polyester. This paper discusses a simple mathematical model to examine the equilibrium of such a membrane under hydrostatic pressure. The model predicts that the maximum displacement of a membrane from the vertical occurs at a depth which varies between l/‐√3 and l/‐√2 , where l is the depth of the canal.     

Time-temperature superposition applied to crosslinked polymers in creep with superimposed hydrostatic pressure

The creep of an epoxy composition under combined tension and hydrostatic pressure (up to 800 kgf/cm²) has been investigated. The applicability of time-temperature superposition to a complex state of stress is demonstrated. Hydrostatic pressure is shown to affect the deformability of crosslinked polymers in tension.Leningrad Technological Institute of the Refrigeration Industry. Plastpolimer Research-Production Association, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 541–544, May–June, 1976.     

Creep of polyester resin PN-3 under moisture-absorption conditions

A procedure is described for testing samples for creep in a climatic chamber of the Feutron 3001 type. Results of an experimental study of forward and back creep of polyester resin PN-3 under simultaneous moistening of samples in an air medium with elevated humidity are discussed. It is shown that the rate of the creep process depends greatly on the humidity state of the material.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 579–584, July–August, 1972.