Effect of hydrostatic pressure on the strength properties of polymer materials

On the assumption that the strength characteristics of homogeneous polymer materials depend on the specific volume, equations are derived for the dependence of the strength or high-elastic limit on the hydrostatic component of the stress tensor and temperature. The ultimate strengths in simple tension, compression and shear are considered in relation to brittle and plastic fracture.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 449–454, May–June, 1969.     

Effect of hydrostatic pressure on the deformation properties of polymer materials

It is suggested that the bulk modulus of homogeneous polymer materials is a function of the specific volume only. The dependence of the bulk modulus and Young's modulus on temperature and hydrostatic pressure is determined on the basis of this assumption. It is shown that the Young's modulus must be higher in compression than in tension. The experimental data are confirmed by the relations obtained. The effect of hydrostatic pressure on the relaxation properties of materials is discussed.Institute of Polymer Mechanics, ASLatSSR, Riga. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 986–991, November–December, 1968.     

Influence of elevated hydrostatic pressure on the diffusion constants of polymer materials

The authors give experimental results showing how the diffusion constants of various polymer materials depend on the (elevated) hydrostatic pressure.A. A. Zhdanov Leningrad State University. Translated from Mekhanika Polimerov, No. 2, pp. 344–346, March–April, 1974.     

Effect of hydrostatic pressure on the viscosity of failure of polymeric materials

Conclusions A setup and method were developed for studying the effect of hydrostatic pressure on the characteristics of the crack resistance of polymeric materials. The viscosity of failure of material K-4I based on butyl rubber was determined in a wide range of rates of crack propagation and hydrostatic pressures. It was found that an increase in the hydrostatic pressure increases the resistance to crack propagation in a polymeric material. The pressure-time analogy method, where the dependences of the viscosity of failure on the rate of crack growth are parallelly shifted to the value of the pressure-time shift and a generalized curve is formed, can be used for taking the effect of the pressure into consideration.Translated from Mekhanika Kompozitnykh Materialov, No. 6, pp. 973–977, November–December, 1986.     

Effect of hydrostatic pressure on certain thermodynamic properties of polymeric materials

By means of a thermodynamic approach it is demonstrated that the mechanical properties of homogenous polymeric materials depend only on specific volume. Expressions are derived for the entropy and volume coefficient of thermal expansion as functions of hydrostatic pressure and temperature. It is shown that for both crystalline and amorphous polymeric materials the bulk modulus depends on reduced temperature.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 825–829, September–October, 1970.     

Effect of hydrostatic pressure on the density of various plastics

It is shown that application of hydrostatic pressure causes an increase in the density of ebonite but practically no change in the density of polyethylene, kapron (nylon-6), PVC, plexiglas, and FKP-1. Uniaxial compression of some materials first increases their mean density, then, at fairly high strain, causes the density to decrease. For the majority of the materials examined, the rate of this reduction in density decreases in the simultaneous presence of hydrostatic pressure.Mekhanika Polimerov, Vol. 2, No. 3, pp. 355–358, 1966     

Study of the impact shear strength of polymer materials

A method is proposed for studying the dynamic strength of block polymers in terms of their resistance to impact shear. An original instrument for conducting tests are room and elevated temperatures is described. The results obtained with this instrument for alkathene and styrene carylonitrile copolymer are discussed. It is found that there is a considerable increase in specific shear energy in the region of transition from the glassy to the high elastic state. In the case of alkathene the investigated characteristic falls linearly on the temperature interval studied.Leningrad Kirov Institute of the Textile and Light Industries. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1135–1137, November–December, 1968.     

Effect of hydrostatic pressure on mechanical properties of plastics

The effect of hydrostatic pressure on the elastic and strength properties of plastics is investigated. Hydrostatic pressure is found to raise the modulus of elasticity, the tensile strength, and the elastic limit. Approximate equations for calculating the strength and elastic properties under various amounts of hydrostatic presure are proposed.Mekhanika polimerov, Vol. 1, No. 1, pp. 65–75, 1965     

Effect of tensile stresses on the strength of heat-treated glass fibers

Possibilities of controlling the internal stresses developing during production of glass reinforced plastics were investigated. A favorable effect can be obtained by prestressing the glass fiber reinforcement during molding. Prestressing during heat treatment was found to increase the strength of the fibers. The strengthening is due to a reduction in stress concentration around microcracks as a result of forced elastic and plastic deformation.Mekhanika polimerov, Vol. 1, No. 1, pp. 89–92, 1965     

The effect of hydrostatic pressure on the crack resistance of particulate reinforced composite materials

The effect of hydrostatic pressure on the fracture toughness of disperse-reinforced composite materials is investigated. It is shown that increased hydrostatic pressure leads to an increase in the critical value of the stress intensity factor and, as a consequence, to an increase in the crack propagation rate. In this case, the pressure-time analogy method can be used to describe the effect of hydrostatic pressure on the characteristics of the crack resistance. This method enables us to represent the experimental data obtained in the form of a generalized dependence of the fracture toughness on the reduced loading rate. Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 1, pp. 121–126, January–February, 2000.     

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.     

Prediction of the short-term strength of polymer materials based on equations of state

The possibility is analyzed of using equations of state for predicting the mechanical properties of linear amorphous polymers with short-term loading from data for their compressibility.D. I. Mendeleev Chemical Technology Institute, Moscow. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 2, pp. 258–262, March–April, 1997.     

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.