Vibrocreep of polymeric materials

The recovery of rigid porous polyurethane after preliminary static and vibrational creep has been experimentally investigated. The effect of a small additional vibrational load on the recovery process is discussed. The results of describing the recovery with the aid of an expression in the form of a Volterra multiple-integral series and a relation of the Leaderman-Rozovskii type are examined.For Communication 6 see [17].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 818–824, September–October, 1970.     

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.     

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.     

Vibrocreep of polymer materials

The vibrocreep of low-density polyethylene (LDP) in uniaxial tension has been investigated in the presence of vibration in the direction of action of the constant load. The material was deformed under nonisothermal conditions owing to heating caused by the dissipation of vibrational energy. Superimposing vibrations leads to a considerable increase in creep rate. It is shown that this increase can not be explained solely in terms of the rise in temperature due to heating of the material; there is also a dynamic creep acceleration effect. Avariant of the vibrocreep approximation with allowance for the dynamic and temperature creep acceleration effects is proposed.Mekhanika Polimerov, Vol. 4, No. 3, pp. 413–420, 1968     

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     

Limiting states of rigid polyvinyl chloride in creep

Creep tests at constant stresses have been carried out on crystalline polyvinyl chloride (PVC) at 16, 40, and 60° to determine its limiting states (i.e., states defining its creep strength, complete cessation of creep strain, and the boundary of the range of invariance of the mechanical properties), which are shown to be described by exponential functions. An approximate method of determining creep is developed; in this method the creep strength is defined as the stress corresponding to the point of intersection of the limiting equilibrium curves and the stress/time-to-rupture curves.Mekhanika Polimerov, Vol. 1, No. 3, pp. 81–86, 1965     

Dynamic stability of a viscoelastic orthotropic cylindrical shell

A method based on the use of Laplace transforms has been developed for reducing the system of equations of motion of a viscoelastic orthotropic cylindrical shell to a single integro-differential equation. The effect of the viscous components on the regions of dynamic instability is investigated (creep due to the action of the shear stresses is taken into account).Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 714–721, July–August, 1973.     

Acoustic creep of glass-fiber-reinforced plastic

A method of investigating acoustic creep of polymer composites developing under the effect of static tensile forces and small amplitudes of dynamic stresses with a frequency of 20 kHz acting coaxially with the static loads is considered. Results of investigating acoustic creep of glass-fabric-reinforced plastic are presented. It is shown that the presence of a high-frequency stress component regularly accelerates relaxation processes and reduces considerably the deformation resistance of the material. Generalized curves simulating the long-time static creep of reinforced plastic are constructed by the method of temperature-time, stress-time, and vibration-time analogies. The results of prediction are compared with the control experiment.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 397–404, May–June, 1973.     

Creep of polyethylene terephthalate with variable stresses under conditions of uniaxial extension

The results from experimental and theoretical investigation of the creep of polyethylene terephthalate film during stepwise varying stresses under conditions of uniaxial extension are given.Izhevsk Mechanical Institute. Translated from Mekhanika Polimerov, No. 5, pp. 929–933, September–October, 1972.     

Bulk deformation during linear extension of certain solid polymers

This article describes an experimental study of the bulk deformation in a forward-and-reverse creep cycle of low-density polyethylene and plasticized acetyl celluloses under stresses beyond the linearity region of the viscoelastic properties.All-Union Scientific-Research Institute of Synthetic Resins, Vladimir. Translated from Mekhanika Polimerov, No. 2, pp. 352–354, March–April, 1974.     

Plane-stress creep of a glass-reinforced plastic

The creep behavior of an orthotropic glass-reinforced plastic based on Polimal'-109 resin and 19-S4 glass fabric is described. A special device for testing tubular specimens in plane-stress creep has been designed. The loading conditions include combined torsion and tension, internal pressure, and loading along the principal directions of anisotropy. Constitutive equations describing creep and recovery are proposed for the two-dimensional case.Warsaw. Translated from Mekhanika Polimerov, No. 3, pp. 398–410, May–June, 1971.     

Calculation of one-dimensional polymer creep under stepped loading

A graphic method is proposed for calculating polymer creep under stepped loading. The method is based on the equations of nonlinear viscoelasticity. It can be used to describe the aftereffects of specimens of polyethylene terephthalate film and the creep of tubular plexiglas specimens at sharply varying stresses. The agreement with experimental data is satisfactory.Mekhanika Polimerov, Vol. 3, No. 4, pp. 671–675, 1967     

Comparison of the effect of ultraviolet radiation on polymer creep rate in a vacuum and in air

The effect of ultraviolet radiation on the creep rates of various polymers has been investigated in a vacuum and in air. It is shown that the ambient medium plays very little part in the processes leading to an increase in creep rate in the presence of ultraviolet radiation.Ioffe Physico-Technical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 559–561, May–June, 1969.     

Effect of the conditions of formation of glued joints on their thermophysical properties

A correlation has been experimentally established between the thermal resistance of adhesive films and the internal stresses that develop during the curing process. During cure the thermal resistance varies in parallel with the internal stresses. It is assumed that the development of thermal resistance is determined by the tension produced in the film by the development of the internal stresses.Voronezh Forest Engineering Institute. Translated from Mekhanika Polimerov, No. 4, pp. 754–756, July–August, 1973.     

Durability of polymers as a function of loading regime during repeated loading with a small number of cycles

Specimens of oriented polycaproamide and unoriented polymethyl methacrylate subjected to uniaxial extension were used to study durability as a function of the number of loading cycles and the intervals between them in different segments of the creep curve. It was shown that the deformation hardening during the initial segment of the creep curve governs the ability of the specimen to withstand subsequent loading cycles. With a relatively low loading rate, deloading-loading cycles during the initial segment of the creep curve lead primarily to an increase in local stresses. During the second stage, repeated loading causes principally an increase in local heating. The interval between loading cycles has only a weak influence on durability.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 252–256, March–April, 1972.     

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.     

Deformability of thermoplastics in physiological salt solution

Conclusions 1. The creep of thermoplastics in physiological salt solution is characterized by change in the rate of creep deformation relative to the creep in air. The bending creep deformations of HMWPE and phenylone and the compressive creep deformation of HMWPE are described by a binomial equation [Eq. (5)] and the compressive creep deformation of phenylone is described by Eq. (6).2. The lifetime of the thermoplastics studied under static compression and bending determined relative to limiting deformations is described by Eq. (7). Under the same stresses and limiting deformations, the lifetime of phenylone in physiological salt solution is greater than the lifetime of HMWPE.3. After the simultaneous action of physiological salt solution and static stress over one month, most of the characteristics of short-term strength in phenylone are significantly reduced due to swelling in the model medium.Paper presented at the Third All-Union Conference on Polymer Mechanics, Riga, 1976.N. N. Priorov Central Scientific-Research Institute of Traumatology and Orthopedics, Moscow. Kazan Construction Engineering Institute. Translated from Mekhanika Polimerov, No. 2, pp. 325–331, March–April, 1978.     

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     

Creep of a thermoplastic cylindrical shell under axisymmetric loading

The solution of the problem of creep of an axisymmetrically loaded thermoplastic cylindrical shell is considered. The strains and stresses for the zero-moment zone and with allowance for the edge effect are predicted on the basis of Kachanov's variational method using a computer. An algorithm is constructed for polyethylene and PVC shells at various values of the load. The analysis of the results obtained is illustrated by the calculation data for individual variants of the program.Leningrad Mozhaiskii Military Engineering Academy. Translated from Mekhanika Polimerov, No. 3, pp. 512–518, May–June, 1969.     

Photoelastic determination of polymer creep stresses and strains

A physical basis provided for the relation between the measured optical quantities and the unknown mechanical quantities in the photoelastic determination of stresses and strains. Questions relating to the "freezing in" of strains are considered in connection with creep tests on models made of optically sensitive polymeric materials. The determination of the stress concentration at the edge of an opening in a strip tested in creep is considered as an example of the application of the theory.Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 739–746, July–August, 1970.