Friction of polymeric materials

The case of contact of polymer and metallic surface has been examined. A formula is proposed for calculating the contact area as a function of time of holding the compression surface under load and for calculating the coefficient of friction, the dependence of Young's modulus and shear strength on temperature, deformation rate, and average force on the contact surface being taken into account. The nature of deformation of irregularities on the surfaces of polymeric materials under the action of normal and tangential loading has been examined.See [1] for Communication 1.Institute for Polymer Mechanics, Academy of Sciences of the Latvian SSSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 809–815, September–October, 1972.     

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.     

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.     

Friction of polymeric materials

The dry friction between a polymeric and a metallic surface is considered on the assumption that the friction power is such that heating of the surfaces can be neglected. The effect of the dimensionless specific load (ratio of nominal stress to elastic hardness of the polymer) on the friction process of elastomers and rigid polymers is analyzed and expressions are given for calculating the coefficients of friction of these materials at large values of the nominal stress.

     

Dynamic loading of polymeric materials

Published material dealing with the dynamic behavior of ductile elastic materials is reviewed. The methods used up unitl now for the investigation of the mechanical characteristics of materials under the conditions of uniaxial stretching and wave propagation are evaluated. There are also presented the basic results of the experimental studies carried out in order to elucidate the effect of rate on the mechanical properties of elastomers, vitrified polymers, glass-reinforced plastics, and crystalline polymers. A review is presented of the experimental and theoretical studies dealing with wave propagation in ductileelastic rods.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 326–338, March–April, 1970.     

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.     

Rheological characteristics of orthotropically reinforced polymeric materials

It is proposed to calculate the rheological characteristics of orthotropically reinforced polymeric materials using a model in accordance with which the composite is assumed to consist of layered blocks, the planes of the layers having one of three possible orientations with given probabilities. The effective rheological characteristics of each block are exactly determined, while those of the composite as a whole are determined in the Voight or Reuss approximations. The first scheme is convenient for calcuating the shear modulus operators, the second for calculating the Young's modulus and Poisson's ratio operators. A numerical computer analysis has been made for the Young's moduli. It is shown that for the anisotropic composites in question each of the technical elastic moduli is characterized by two resolvent Q* operators of real or complex argument. The conditions under which one of the Q* operators can be neglected are determined. The integral representation of the kernel of the Q* operator of complex argument is given in the case where the latter is fractional-exponential with fractional index =–1/2 and the corresponding curves are presented.Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 276–283, March–April, 1972.     

Machines for physicomechanical testing of polymeric materials

Two tensile-testing machines are described for physicomechanical tests of polymeric materials with deformation up to 100 and 1,000% in which the conditions of deformation are assigned directly to the measurement base of the specimen by using an automatically regulated electric drive, ensuring parity of the measured quantity (force, elongation, or stress) with the requisite preset functional controller.     

Structure and properties of magnetic fibrous polymeric materials

Characteristic features of the filtration of liquids by magnetic fibrous polymeric materials (MFPM) are addressed; these materials are a set of fibers of a polymeric material containing a ferritic filler; they are adhesively bound at points of their intersection. It is demonstrated that variations in structural parameters (fiber thickness, distribution of fiber throughout the material, and its concentration), as well as the degree and direction of magnetization of the MFPM exert an influence on the efficiency of the liquid filtration. Optimum parameters for MFPM designed to purify liquids of ferromagnetic and nonmagnetic contaminants are given.A paper to be presented at the Ninth International Conference on the Mechanics of Composite Materials, Riga, October, 1995.Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 3, pp. 291–297, May–June, 1995.     

Testing methods for predicting the life of polymeric materials

On the assumption that the performance of polymeric materials can be predicted only on the basis of long-time tests under conditions similar to those that obtain in practice, the authors consider creep, stress relaxation, and dynamic measurements at various temperatures and frequencies. Theoretical methods of estimating the life of polymeric materials are investigated with allowance for changes in the physical and chemical structure of the polymer and the nonconstancy of the activation energy of the relaxation processes over a broad temperature interval.Lenin Moscow State Pedagogical Institute, Laboratory of Problems Polymer Physics. Translated from Mekhanika Polimerov, No. 2, pp. 212–220, March–April, 1971.     

Temperature - time analogy for thermorheologically complex polymeric materials

Conclusions 1. The viscoelastic properties of mixtures of crystalline polymers with elastomers have been studied as functions of temperature. It is shown that, for mixtures of PP with PIB and TEP, the concept of thermorheologically simple behavior is applicable only within a narrow interval of temperature.2. Parameters of the temperature—time analogy for thermorheologically complex materials have been calculated. It is established that, at temperatures above a characteristic temperature T*, a strong dependence of the correction coefficient on time and a strong dependence of the relaxation function on the ratio of components exist.3. It is shown that use of the concept of thermorheologically complex behavior for prediction of the long-term deformability allows analysis of the contributions of specific components to the viscoelastic behavior of the mixture in different temperature intervals.Paper presented at the Third All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1976.Okhtinsk Scientific-Industrial Association "Plastpolimer," Leningrad. Translated from Mekhanika Polimerov, No. 4, pp. 614–620, July–August, 1977.