Polymer breakdown and fatigue

Problems of the mechanical breakdown of polymer materials are discussed on the basis of kinetic considerations on such breakdown, viewed as a thermofluctuation-induced process of an accumulation of breaks in interatomic bonds (either break or damage). The present state of this problem is analyzed, both for static and for cyclic loads (fatigue). Some approaches for developing a theory of breakdown are reviewed. Theories related to the accumulation of damage in the volume of the sample receive particular attention. Recent studies on fatigue in polymer materials are listed.Paper presented at the 2nd All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1971.A. I. Ioffe Physicotechnical Institute, Academy of Sciences of the SSSR, Leningrad. Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 597–611, July–August, 1972.     

Supersonic crack propagation in blocks of polymethyl methacrylate

It is shown that a giant laser pulse can cause supersonic crack propagation in PMMA. The results of the experiments and a microstructural analysis of the fracture surface are presented. A study of the microstructure shows that supersonic crack propagation is associated with the propagation of a shock wave in the focal region.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1027–1029, November–December, 1971.     

Polymer friction

The results of research on the antifriction properties of polymeric materials and expressions for calculating their coefficient of friction are presented. The effect of the mechanical properties of the materials on their antifriction characteristics is discussed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 421–429, May–June, 1975.     

Experimental investigation of the correspondence between quasistatic tension and longitudinal wave propagation in a polyethylene rod

The propagation of longitudinal waves created by the impact of a rigid mass against a polyethylene rod of finite length has been investigated. The experimental procedure is described and oscillograms of the process are presented. The relaxation spectrum is calculated from the experimental data on the mechanical behavior of the material over a broad range of strain rates. The results of the experiments are compared with a numberical solution of the problem of the impact of a rigid mass against a rod whose material is characterized by a relaxation spectrum.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 564–567, May–June, 1971.     

Energy dissipation in a glass laminate stressed in cyclic tension-compression

An experimental investigation has established that in a glass laminate most of the mechanical losses are converted into thermal energy. The sum of the mechanical losses increases with increase in the fatigue life of the material, the ratio of thermal losses remaining constant under given deformation conditions. Quantitative data are presented for the energy dissipation in various phases of the fatigue fracture process.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 655–661, July–August, 1969.     

A linearized theory of thermoviscoelasticity

A generalized linearized theory of thermoviscoelasticity, including the effect of heat formation, is presented. The linearized equations of motion, of state, and for the energy are given together with the linearized boundary conditions for large initial deformations. Attention is drawn to the fact that the equations which have been derived can be used for the solution of problems concerning the stability of viscoelastic bodies, the propagation of waves in viscoelastic materials which are subjected to deformation, and problems concerning the stress-deformed state of viscoelastic elements. The problem of the propagation of plane waves in viscoelastic materials which are subjected to deformation is considered as an example.Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 2, pp. 214–221, March–April, 1972.     

Mechanical characteristics of radiation-cured glass-reinforced plastics

Data are presented on the mechanical characteristics of oligoester maleates copolymerized with styrene and the corresponding glass-reinforced plastics crosslinked by the thermochemical and radiation methods. It is established that the radiation-cured glass-reinforced plastics have improved strength and stiffness as compared with similar specimens obtained by thermochemical curing.Institute of Mechanics, Institute of High Molecular Compounds, Institute of Physical Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 4, pp. 704–710, July–August, 1969.     

Periodic deformation and viscous flow of polymer melts and solutions (communication 1)

The principles of the theory of thixotropy are formulated. The basic relations are obtained for cases of periodic vibration superimposed on shear flow. The effect of stationary shear flow on the linear dynamic characteristics of an elastic liquid is investigated. The calculated values are compared with the experimental data.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 519–527, May–June, 1969.     

Comparative analysis of certain particular cases of approximation of experimental data

It is shown with reference to examples concerning the prediction of the mechanical and deformation properties of polymeric materials that the use of the linearization method for approximating the experimental data with certain functions, with the object of subsequently determining their parameters by least squares, is not always justified and may lead to significant errors. In particular, the determination of the parameters of the relation for the time-temperature shift factor and the approximation of certain experimental data by means of power and exponential functions are considered.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 725–728, July–August, 1974.     

Investigation of longitudinal wave propagation in a polyethylene rod

Longitudinal wave propagation in a polyethylene rod has been investigated. A computer has been used to obtain a numerical solution of the problem of wave propagation in a rod, whose material is described by the Boltzmann-Volterra equation. The results of the computations are compared with the experimental data. The method of characteristics is employed to construct the dynamic – diagrams for the case of wave propagation in a prestressed rod on the basis of the model of a viscoelastic standard solid.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 59–67, January–February, 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.     

Application of the dislocation theory of fracture to polymeric materials

The macrocharacteristics of the mechanical strength of crystalline polymers are estimated on the basis of the dislocation theory of fracture. The values obtained for the breaking and safe stresses and the necking stress are in good agreement with the experimental results.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 549–551, May–June, 1971.     

Periodic deformation and viscous flow of polymer solutions and melts

The transition from the start of deformation to the establishing of a stationary state of nonlinear, periodic shear deformation and the kinetics of the change in the mechanical characteristics after deformation at finite amplitudes has ceased have been investigated. The calculated values have been compared with those obtained experimentally.For Communication 2 see [3].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Institute of Mechanics Problems, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 521–529, May–June, 1970.     

Periodic deformation and viscous flow of polymer solutions and melts

The effect of nonlinear periodic deformation on the relaxation spectra and viscous-elastic characteristics of polymer melts and solutions is considered. The experimental and calculated relationships between the dynamic characteristics and effective viscosity and the amplitude of the rate of periodic deformation were compared.For Communication 1, see [6].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Institute of Mechanics Problems, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 357–366, March–April, 1970.     

Creep of unidirectional glass-reinforced plastics based on new types of fibers

Theoretical and experimental compressive creep relations for a unidirectional glass-reinforced plastic based on hollow fibers are presented. The agreement between the theoretical and experimental data is shown to be satisfactory. The effect of fiber capillarity on the creep process is unimportant.All-Union Scientific-Research Institute of Glass-Reinforced Plastics and Fiber Glass, Moscow; Institute of Mechanics of Machines and Polymeric Materials, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Mekhanika Polimerov, No. 4, pp. 747–750, July–August, 1971.     

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.     

Numerical solution of the impact problem for a rigid mass and a viscoelastic rod of finite length

The problem of the propagation and interaction of longitudinal waves in a rod struck by a rigid mass is considered. A numerical computer solution is obtained for the case when the mechanical behavior of the rod material is expressed by a rectangular relaxation spectrum. A numerical method of integral transform inversion is developed and applied to problems of polymer dynamics.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 450–456, May–June, 1971.     

Modeling the creep stability of plastic shells

The problem of modeling the creep stability of shells is investigated on the basis of the strain compatibility, equilibrium and physical equations, and the boundary conditions. The mechanical similarity of physically nonlinear elastic and elasto-hereditary materials is examined in detail. The concept of an elastic potential and Volterra-type integral relations with increasing multiplicity are employed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1059–1063, November–December, 1969.     

Concerning the investigation of the supermolecular structure of polymers with a three-dimensional network

The results of an investigation of the structure and properties of a series of crosslinked polymers are presented. It is shown that the structure is determined by the chemical structure of the starting components and the method of synthesis.Institute of Chemistry of High-Molecular Compounds, Academy of Sciences of the Ukrainian SSR, Kiev. Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 5, pp. 934–936, September–October, 1970.     

Composites reinforced with a system of three straight mutually orthogonal fibers

The effectiveness of reinforcement in direction 3 has been estimated by investigating the mechanical characteristics of two types of three-dimensionally reinforced materials differing with respect to the arrangement of the reinforcement and the fiber content in each direction. The superior transverse stiffness, shear strength, and transverse tensile strength of three-dimensionally reinforced composites based on a system of three mutually orthogonal fibers, as compared with laminated materials, is demonstrated. The theoretical values of the elastic constants, calculated from the relations of [5], are compared with the experimental data.For communication 1 see [5].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1011–1018, November–December, 1973.