Terminal defects in crystalline polyethylene

Conclusions 1. Possible modes of transverse movement of terminal defects in crystalline polyethylene have been investigated for the three-dimensional case. It has been found that the probability of aggregation of two columns of monovacancies by means of their transverse movement decreases rapidly with increase in the initial distance between defects.2. The process of decrease in volume of a column of vacancies during compression has been investigated. A dependence of the degree of compression of a vacancy on the angle between the external force and the plane of zigzag of the chain has been found.3. Three positions of stable equilibrium of doubling of the three-dimensional model of polyethylene containing a series of vacancies have been observed during loading of the simple shear type.For Communication 1, see [1].Institute for Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 588–595, July–August, 1978.     

Terminal defects in crystalline polyethylene

Conclusions 1. It was shown that the terminal defect in polyethylene contains a set of partial twist disclinations with different Frank vectors for different chains.2. It was found that the structure of the terminal defect changes during elongation of the chain and outward from the crystallite. It was also found that the volume of the void formed by the presence of the chain and remains constant; the elongation process is accompanied by a conservative motion of the disclination loops along the chains, which causes creep of the screw dislocations.3. The conformational changes were calculated for a segment moving in the crystal field of neighboring chains in regular and high-pressure PE; the values of the energy of activation of the chain and motion were obtained (10.3·10^–16 and 3.6·10^–16 erg/monomer for the regular and high-pressure PE, respectively), indicating a higher rate of annealing of PE in the high-pressure phase.For communication II, see [2].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 793–798, September–October, 1978.     

Accumulation of fatigue defects in polymethyl methacrylate in rotational bending

The results of tests on polymethyl methacrylate for fatigue during polycyclic rotational bending through an angle under thermostatic conditions are analyzed. A method of calculation is given for the determination of the defects. The observed changes in the mechanical characteristics and the fractography of the fractures are taken into account comprehensively. Possibilities for the simplification of the method of calculation, and the acceptable methods for the indication of defects before the formation of the main crack are discussed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1038–1045, November–December, 1974.     

Critical levels of oriented defects in brittle fracture

Conclusions For an orthotropic system of defects we derived a brittle failure criterion whose coefficients are determined by the parameters of the structure. The discussed examples show that the proposed relationships can be used more efficiently to determine the behavior of the structure on the basis of the macroproperties of the material. The effects of variations in the dimensions of the defects, merging of the defects and the appearance of new defects are described quantitatively. After compiling a sufficient amount of information, the relations can be used to solve the main problem of determining the ultimate strength on the basis of the behavior of the structure of defects.Translated from Mekhanika Kompozitnykh Materialov, No. 4, pp. 623–630, July–August, 1989.     

Effect of antioxidant distribution in polycaprolactam on the variation of strength and deformability at elevated temperatures

The effect of quinhydrone distribution over the cross section on the strength and deformability at elevated temperatures has been investigated for specimens of polycaprolactam. The optimum concentrations of quinhydrone in the surface layer of polycaprolactam retaining maximum strength over an extended period in a hot-air medium have been determined. The most probable areas of formation and localization of structural defects under thermal action have been established.Mekhanika Polimerov, Vol. 3, No. 2, pp. 296–301, 1967     

Buildup of defects in polymethyl methacrylate in service and their effect on its notch sensitivity

This study deals with the effect which defects built up in polymethyl methacrylate during 0–16,000 h of service have on its physicomechanical properties, fracture topography, and notch sensitivity. The trend of strength and plasticity characteristics is established as well as that of the coefficients of notch sensitivity as functions of the notch depth.Lenin Institute of Civil Aviation Engineers. Translated from Mekhanika Polimerov, No. 2, pp. 256–262, March–April, 1976.     

Effect of powdered mineral fillers on the crosslinking of phenol-formaldehyde oligomers and the mechanical properties of the molding materials

By investigating the effect of various powdered oxides on network formation in phenolformaldehyde oligomers, it has been established that nonionogenic oxides increase the number of network defects in proportion to the surface energy of the powder. Small amounts of ionogenic oxides with a divalent cation cause the formation of new ionic or ionic-coordination linkages in the polymer network. The effect of mineral powders on polymer network formation is correlated with the mechanical properties of molding materials based on phenol-formaldehyde polymers with different network densities.Moscow Aviation Technological Institute. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1033–1042, November–December, 1968.     

Concentration of electroelastic fields in a composite piezoceramic plate with defects crossing the interface

The characteristics of fracture and strength of a composite piezoceramic plate with defects in the form of cracks and holes situated in both of the plate components are investigated. The corresponding boundary-value problems of electroelasticity are reduced to systems of singular integral equations by constructing integral representations of the complex potentials. The results of numerical realization of the constructed algorithms are reported.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 6, pp. 777–786, November–December, 1998.     

Vibration analysis of a disordered polymer chain

A variational method is used to make a numerical calculation of the vibrations of a disordered polymer chain. A curve is constructed for the square of the frequency and the parameters of the trial function as functions of the mean phase difference between neighboring atoms. The results are compared for three forms of the distribution function for the force constants and, moreover, for two variants of the variational method and the direct calculation for a finite chain.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 771–776, September–October, 1971.     

Strength of boron fibers

The tensile and flexural strength and elastic properties of continuous boron fibers 95–105 µ in diameter obtained by depositing boron on a tungsten filament 10–12 µ in diameter have been investigated. The strength properties are primarily determined by the defects present at the boron sheath-core interface and for the fibers investigated have a limit of approximately 400 kgf/mm². Coarse surface or internal defects are capable of reducing the strength of the fibers to 200–250 kfg/mm².All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1126–1127, November–December, 1970.     

Plastic deformation of models of a crystalline polymer with increased lattice defectivity

Conclusions 1. On the basis of two-dimensional models, the structure of a polymeric crystal containing more than one lattice defect has been determined on an electronic computer. The types of defects are: a) double vacancy, model I; b) two isolated vacancies, model II; c) a combination of isolated vacancies and double vacancies, model III. Plastic deformation curves have been calculated for all three models.2. It has been observed that increase in the degree of defectivity in a crystalline polymer significantly reduces the elastic limit and reduces the strength limit of the structure very little. The elastic limit falls particularly strongly with increase of the defectivity in a state of hydrostatic stress.3. Increase in the density of crystallographic defects causes significant mutual rearrangement of the coordination polygons of the crystal lattice, which occurs as the result of plastic deformation.Report presented at the Third All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1976.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 397–402, May–June, 1977.     

Measuring the stresses in fibers of a loaded composite material by the method of infrared spectroscopy

Conclusions 1. Actual stresses in reinforcement fibers of a loaded composite have been measured by infrared spectroscopy.2. It has been shown that the plain rule of mixtures, not accounting for changes in mechanical properties of the matrix during processing of a composite, does not apply to a hot molded polyethylene-polypropylene composite.3. It is suggested that around the reinforcement fibers there exists an ordered layer of the matrix material capable of carrying a heavy load. A method is proposed, furthermore, for calculating the mechanical characteristics of the composite with such a layer. The volume fraction and the thickness of this hardened layer have been estimated from experimental data.Paper presented at the Third All-Union Conference on Polymer Mechanics in Riga, 1976.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 832–837, September–October, 1977.     

Origin of laser damage in transparent dielectrics of the plexiglas type

A gasification mechanism is proposed. This mechanism is based on multiphoton photodegradation of the polymer molecules and the resulting formation of free radicals which trigger a chain reaction and the subsequent formation of gas molecules. The kinetics of this process, in which an important part is played by the microstructure of the material, are examined.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 232–238, March–April, 1973.     

Effect of thermal treatment temperature on the structure and properties of carbon fibers

Conclusions 1. It has been shown that the presence of a maximum in the dependence of strength on Young's modulus for carbon fibers made from PAN fiber may be explained by an effect of the process of temperature stress accumulation which takes place under the conditions of isometric heating. The start of this process, which causes a rearrangement of the internal structure of the high-modulus fiber, coincides with the start of the anomalous rise in fiber density.2. The interconnection between surface and internal defects and the elastic-strength properties of carbon fibers made in the temperature treatment range 600–3000°C has been studied.3. Original data on the elastic-strength properties of borided carbon fibers have been obtained; the structure of these is marked by a high degree of perfection. It has been shown that in boriding, which facilitates graphitization of the carbon, the process of regular reduction in fiber strength which is reached in the precrystallization stage is somewhat retarded.All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1036–1042, November–December, 1976.     

Effect of the end conditions on the critical loads for filament-wound glass-reinforced plastic columns

The behavior of glass-reinforced plastic columns with various end conditions has been experimentally investigated. The cross-wound columns had a length to mean diameter ratio of 18–20. Four types of support with different degrees of restraint on end rotation ranging from almost free ends to fixed ends were employed. The possibilities of increasing the critical loads by manipulating the boundary conditions are estimated. Numerical estimates are obtained for the various methods of support. Random imperfections and the number of loadings were not found to have any effect on the critical loads. It is shown that the use of Southwell's method makes it possible to estimate the critical loads for columns with different end conditions from the subcritical loading data.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 54–62, January–February, 1976.     

Spinel fibers for ceramics

The process of formation of a fibrous spinel in the Al₂O₃–MgO system is investigated. The dependences of the spinel structure and properties on technological parameters of the process of synthesis is studied. Optimal relations between the fiber constituents for obtaining a stoichiometric spinel are determined and a two-stage mechanism of its formation has been found. Some ceramic materials are obtained from fibrous dispersions, and their physicomechanical characteristics have been estimated.Institute of General and Inorganic Chemistry, Belarus National Academy of Sciences, Minsk, Belarus. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 4, pp. 509–516, July–August, 1999.     

Effect of quartz sand filler on the mechanical and thermophysical properties of alkyd and epoxy coatings

The effect of a filler on the mechanical and thermophysical properties of polymer coatings has been investigated. It is shown that quartz sand particles are centers of structure formation in alkyd and epoxy coatings. It has been found that a denser, oriented, and stressed polymer structure, much exceeding the size of the individual macromolecules, is formed around the filler particles. The size of the spheres around the filler particles depends on the nature of the film-former, on the filler surface, and on the filler content. It is postulated that secondary supermolecular structures, and not individual polymer macromolecules, are adsorbed on the surface of the filler particles.Mekhanika Polimerov, Vol. 3, No. 3, pp. 507–510, 1967     

Effect of small vibrations on cracking kinetics in polymethyl methacrylate. Concept of a rate-dependent cracking resistance. Possible thermal mechanism

Conclusions 1. Small vibrations superposed on the main static component of an external load cause the cracking rate in polymethyl methacrylate to increase appreciably. Within the range of low cracking rates (<10^–4 cm/sec), evidently most important from the practical standpoint, the cracking resistance of this material is also found to decrease.2. The concept of a rate-dependent cracking resistance applies to conditions under a vibration load, over a wide range of vibrations at low or intermediate cracking rates.3. The effect of small vibrations is local in nature. It may have to be taken into account, if cracks or similar defects already exist in a structure or appear in it during service.4. The thermal mechanism is not adequate for quantitatively describing the experimentally observed effect of vibration.Paper presented at the Third All-Union of Conference on Polymer Mechanics in Riga, 1976.M. V. Lomonosov Moscow State University. Translated from Mekhanika Polimerov, No. 5, pp. 846–853, September–October, 1977.     

Thermoelastic processes in deformable solid bodies with point defects

We propose a thermodynamic model and obtain a closed system of differential equations describing the thermoelastic processes jointly with the redistribution and recombination (generation) of point defects in deformable solid bodies.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 28, 1988, pp. 18–21.     

Deformation of the glass in the zone of formation of a hollow glass fiber

An equation has been derived for the deformation of the glass in the zone of formation of a hollow glass fiber, and the nature of the deformation along the length of the "bulb" has been determined. The principal technological factors controlling the capillarity coefficient of the fiber have been established and their interactions are shown to affect the geometric characteristics of the fiber. The region of existence of the hollow fiber formation process has been determined. There is satisfactory agreement between the experimental and theoretical data.All-Union Scientific-Research Institute of Glass-Reinforced Plastics and Glass Fiber, Moscow Region. Translated from Mekhanika Polimerov, No. 4, pp. 599–603, July–August, 1973.