Investigation of the effect of an electrical field on the mechanical strength of polystyrene film

The effect of an electric field on the time dependence of the mechanical strength of a polystyrene (PS) film is investigated at different values of voltage and duration of exposure. It is found that at first the strength of the PS film drops with exposure to the electric field and then slowly increases.Mekhanika Polimerov, Vol. 1, No. 6, pp. 78–84, 1965     

Creep and long-time strength of tubular specimens of asbopolyethylene

Results are presented of an experimental investigation into the mechanical properties of asbopolyethylene obtained by adding 25 parts by weight of asbestos to pure low-density polyethylene to improve strength and stiffness characteristics. Test data on the creep and static strength of tubular specimens of asbopolyethylene at room temperature in uniaxial tension are given. The long-time strength of asbopolyethylene was determined at 20°, 50°, 80° and 100° C. To estimate the effect of adding asbestos to the polyethylene the mechanical characteristics of pure polyethylene and asbopolyethylene are compared.Mekhanika Polimerov, Vol. 1, No. 5, pp. 51–57, 1965     

Impact strength of high-density polyethylene with various molecular weight distributions

The Charpy impact strength of high-density polyethylene specimens prepared under low pressure with average molecular weight from 60·10³ to 1.5·10⁶ and differing substantially in molecular weight distributions has been studied at room temperature and at –190°C. It is shown that, both at room temperature and at temperature considerably below the glass-formation temperature, the impact strength of polyethylene in the range of molecular weights mentioned is determined mainly by the content of fractions with molecular weights about 10⁵ and more and does not depend on the width of the molecular weight distribution."Plastpolimer" Scientific-Research Association, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 919–921, September–October, 1973.     

Effect of molecular weight on strength and deformation characteristics of oriented amorphous polymers

Tensile tests were carried out on uniaxially oriented films of several amorphous linear polymers (polymethyl methacrylate, polystyrene, and poly-2,2-octamethylene-5,5-dibenzimidazol) of various molecular weights. It was shown that molecular weight has no direct effect on polymer strength, which is determined by structure. However, when polymer fibers and films are formed and stretched, the molecular weight of a given material affects the orientation of macromolecules and so predetermines the structure of the products obtained and, consequently, their strength.Mekhanika Polimerov, Vol. 3, No. 4, pp. 579–585, 1967     

Fracture mechanism of amorphous polystyrene

The degradation products of polystyrene film specimens have been recorded and their accumulation kinetics in the presence of uniaxial tensile stresses have been studied at various temperatures. It is shown that the accumulation kinetics satisfy the Arrhenius equation for reactions in a mechanical field. The equation for the rupture life can be written in terms of the corresponding parameters of the mechanical degradation reactions. It is concluded that the rupture life and strength of polystyrene depend on the kinetics of mechanical degradation of the polymer chains.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 541–544, May–June, 1975.     

Strength properties of polymer films subjected to continuous tearing

Using the principle of tearing at a constant velocity and applying this to samples with longitudinal notches, a method of recording the tearing strength as a continuous function of temperature, crystallization time, and other factors which continuously vary the state of a (polymer) film material is developed. The characteristic points of the temperature transitions are determined for a number of polymer films in relation to their mechanical (strength) properties. The crystallization kinetics of polyethylene terephthalate films are analyzed.Scientific-Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 257–261, March–April, 1972.     

Study of the effect of various factors on the low-temperature strength of polyethylene with graft polyacrylonitrile

Low-density polyethylene film has been subjected to graft polymerization with acrylonitrile. The effect of the graft polymerization conditions and subsequent treatment on the strength of the grafted film has been investigated. The strength was measured at -196°C. The grafted film behaves like a heterogeneous material in which the unoriented polyacrylonitrile macrostructures play the part of filler particles. The strength of the grafted film is additively composed of the strengths of the polyethylene and the polyacrylonitrile and the change in strength after stretching, heating, and other treatments is determined by the changes in the degree of orientation of the polyethylene.V. I. Lenin Belorussian State University, Minsk. Translated from Mekhanika Polimerov, No. 4, pp. 589–593, July–August, 1973.     

Effect of the molecular weight of the polystyrene matrix on the physicomechanical properties of impact polystyrene

The effect of the molecular weight of the polystyrene on the properties of impact polystyrene obtained by mechanical mixing of polystyrene and rubber has been investigated. As the molecular weight of the polystyrene increases, the physicomechanical properties of the impact polystyrene improve and its rheological properties deteriorate. There is a definite correlation between the physicomechanical properties of the polystyrene and those of the impact polystyrene.Scientific-Research Institute of Synthetic Rubber, Kralupy-on-Vltava, Czechoslovakia. Translated from Mekhanika Polimerov, No. 3, pp. 545–546, May–June, 1971.     

Effect of certain additives and the ambient medium on the static and fatigue strengths of polyamides

The change in the static strength of polycaprolactam during heat treatment has been investigated in relation to the type of additive and the ambient medium, and the change in dynamic strength in relation to the method of introducing the stabilizer. It has been observed that there is a slowdown in the thermal oxidation and loss of strength of polyamides exposed to heat in a medium containing stabilizer vapors and of polycaprolactam heat-treated after being coated with lacquer containing a thermostabilizer.On the basis of the experimental material it is suggested that the loss of strength of polyamides associated with thermal oxidation is due principally not to a reduction in molecular weight or crosslinking but to stress concentrations and microdefects associated with rupture of the molecular chain. An effective method of increasing the dynamic strength of polyamides has been found.Mekhanika Polimerov, Vol. 2, No. 1; pp. 60–66, 1966     

Thermomechanical method for determining the molecular weights of amorphous linear polymers

A thermomechanical investigation of polyisobutylene specimens under various time and stress conditions enabled us to extend the applicability of this method of determining the molecular weight of an undissolved polymer. The previously proposed mechanical model of a polymer, which is the basis of the relationship between the molecular weight of the polymer and the difference between the yield and glass-transition temperatures, must be refined to make allowance for the supramolecular structure.Mekhanika Polimerov, Vol. 3, No. 4, pp. 586–590, 1967     

Effect of elevated temperatures on the strength of cured resins and resin-based materials

An analysis of the relationship between the relative changes of compressive strength and weight loss for glass laminates has shown that at elevated temperatures (to 600° C) the changes in strength are primarily caused by processes of mechanical destruction of the resin phase. The process of thermo-oxidative degradation of the resin in the laminate is described by the same stages as were detected in studying cured resins.Moscow Aviation-Engineering Institute. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 832–838, September–October, 1968.     

Control of biopolymer poly-β-hydroxybutyrate characteristics by γ-irradiation

The influence of γ-irradiation on the structure and some mechanical properties of poly-β-hydroxybutyrate was studied. Specimens of PHB were γ-irradiated with various doses (1–20 Mrad) in air and vacuum. The molecular weight, structural characteristics of the crystalline and amorphous phases, characteristics of thermal degradation, and deformation of the polymer were determined. The crystallinity was found to increase with increase in the radiation dose and with the corresponding reduction in molecular weight. The increase of crystallinity was the greater the smaller the length of macromolecules (higher radiation dose). The melting temperature T _m , which characterizes the crystalline order, decreased with decrease in the molecular weight. The results of calorimetric studies suggest that radiation-caused degradation, which occurs at a temperature at which “cold” crystallization (60°C) is possible, might also affect the crystalline part of the polymer.     

The effect of C<Subscript>60</Subscript> fullerene on the toughening of epoxy compositions

The effect of C₆₀ fullerene on the mechanical properties of epoxy resins has been investigated. It is found that this filler affects the tensile modulus and tensile strength of epoxy compositions only slightly, but their impact strength at a 0.01–0.12 wt.% content of C₆₀ increases by about 100–200%. A molecular mechanism of the toughening effect of C₆₀ on epoxy resins is suggested.     

Current state and prospects for development of the physical theory of brittle strength of polymers

Various mechanisms of brittle fracture and theories of the time dependence of the strength of rigid polymers are examined. The effect of various types of mechanical losses (deformation, dynamical, surface) on polymer strength and life is analyzed. The principal shortcomings of Griffith's theory of strength are pointed out. From an examination of the two basic mechanisms of brittle fracture of polymers-nonthermal and thermal (thermal fluctuation)-it is concluded that the latter is the more important. A comparison is made of the fluctuation theory of polymer strength with new experimental data on polymethyl methacrylate, and the causes of the transition from brittle to nonbrittle fracture are discussed. The effect of molecular orientation on the strength of polymers is examined on the basis of the fluctuation theory of strength.Mekhanika Polimerov, Vol. 2, No. 5, pp. 700–721, 1966     

Strength of rigid oriented amorphous polymers

A method is proposed for obtaining uniaxially oriented specimens of amorphous unfractionated polymer with a particular oriented chain length. The length of the oriented chains and their molecular weight M_c depend importantly on the conditions under which the polymer is stretched. It is shown that the strength of specimens obtained by stretching at constant M_c increases linearly with the relative fraction of oriented phase. The slope of this linear relation increases with the length of the oriented molecular chains. The ratio of the maximum strength of fully oriented polystyrene to the strength of the unoriented material is found to be 78 instead of the value of 6 given in [6].Mekhanika Polimerov, Vol. 3, No. 6, pp. 1048–1053, 1967     

The problem of strengthening of plastics in polymer solvents medium

It was found that short-term treatment of unstressed acrylate AST-T samples with n-amyl alcohol and butyl acetate leads to a marked improvement in their mechanical properties. The influence of temperature, holding time, and the nature of the solvent on the strength of acrylate AST-T has been studied. The increase in the strength indexes is the result of the thermal effect of the medium on the molecular structure of the surface layers and healing of the surface defects of the material. The great importance of the state of the surface on the physicomechanical properties compared with the temporary plasticizing action of the solvents has been shown.V. I. Lenin Kharkov Polytechnic Institute. Translated from Mekhanika Polimerov, No. 5, pp. 913–915, September–October, 1972.     

Biaxial orientation of amorphous linear polymers

The mechanical properties of biaxially oriented polymethyl methacrylate, obtained on a broad range of stretch ratios and under a variety of orientation conditions, have been investigated. There is a fundamental difference between the variation of the forced elastic limit with increase in stretch ratio, which is monotone increasing, and the variation of such properties as the brittle strength, brittle temperature, true strength and elongation at break, which have an optimum at a certain stretch ratio. It is shown that the presence of an optimum is associated with the transformation of the supermolecular structures in the process of biaxial high-elastic deformation. A relation is established between the mechanical properties of biaxially oriented polymethyl methacrylate (orientation hardening) and the density of the molecular network.For communication 1 see [3].Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 586–593, July–August, 1971.     

Load bearing capacity of multilayered sectional tubular rods made of composites

Conclusion We investigated the load bearing capacity of a new class of tubular rods made of composites, viz., peripherally and radially sectional. It was discovered that under conditions of tension, compression, bending, and combined loading by compression and torsion the number of macrolayers, strengthening by a carcass or external lagging have practically no effect on the rigidity and strength of peripherally and radially sectional rods. The nature of failure of sectional and monolithic rods is the same. Ways were shown of increasing the load bearing capacity of the rods under consideration with the object of bringing their mechanical properties up to the level of monolithic rods by improving the technology of assembly and by using high-strength film glues.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 85–92, January–February, 1990.     

Orientation stretch and the strength of crystallizable polymers

Changes in the orientation of molecules present in the amorphous and crystalline phases during orientation stretching of polymers are considered, as well as connections between these processes and the mechanical strength of solid oriented specimens. The studies were conducted on films of crystallizable polymers — polyvinyl alcohol and polyethylene. In explaining the dependence of the strength of specimens of these polymers on molecular orientation, the polymers are considered as three-component compositions.     

Molecular statics simulations of ferroelectric nanofilms

Smart materials are of great interest not only for scientific, but also for technological reasons due to ongoing miniaturization and rapid developments in manufacturing technologies of nanocomponents [1]. Therefore, simulations on the nanometer length scale are becoming more important in order to fundamentally understand and predict the complex material behavior of ferroelectric nanocomponents, such as ferroelectric nanofilms or nanowires. We apply a previously developed extended molecular statics algorithm [2] to simulate ferroelectric barium titanate nanofilms. The algorithm is able to also consider mechanical stress explicitly whereas most molecular simulations of ferroelectrics are restricted to NVT-ensembles. We simulate a stress relaxed ultra thin barium titanate film and apply compressive strain in order to investigate size effects of ferroelectric nanofilms. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)