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     

Strength of biodegradable polypropylene tapes filled with a modified starch

The possibility of creating composite materials with high deformation and strength characteristics based on polypropylene (PP) and a natural polysaccharide in the form of a modified starch (MS) has been studied. The modified starch is shown to interact chemically with functional groups of PP, thereby positively affecting the physicomechanical properties, structure, and water absorption properties of films and oriented flat fibers based on starch-filled PP. The strength characteristics of both oriented and unoriented composites are 1.5–2.0 times as high as those of the initial PP. The water absorption ability of the materials varies symbatically with content of MS, which points to the dominant contribution of interactions at the PP-MS interface. The introduction of MS into synthetic polymers offers a possibility of producing new ecologically safe materials with high strength characteristics. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 3, pp. 389–400, May–June, 2006.     

Effect of the conditions of bond formation and destruction on the adhesion of polymers to synthetic fibers

It is shown that the adhesion of linear polymers can be measured by shearing a monofilament relative to a microblock of adhesive [1]. Experiments have been performed on polypropylene, polyethylene terephthaliate, polycaprolactam, polyvinyl alcohol, and glass fibers. Broad variation of the diameter, structure, and physicomechanical properties of the various kinds of oriented fibers had practically no effect on the adhesion. The physicochemical properties of the adhesive solutions at the moment of application to the fiber likewise do not affect the adhesion which, other things being equal, is determined by the nature and supermolecular structure of the polymers in the contact zone.Belorussian Lenin State University, Minsk. Branch of the Karpov Scientific-Research Physicochemical Institute, Obninsk. Translated from Mekhanika Polimerov, No. 6, pp. 1042–1048, November–December, 1970.     

Polypropylene reinforced with aramid and glass fibers

The effect of the chemical nature of the aramid fibers Phenylone, Terlon, Armos, and SVM on the mechanical, thermophysical, and antifriction properties of reinforced polypropylene was investigated. It was found that the composite filled with SVM fibers based on a stiff-chain polymer has high tensile strength and bending modulus. Reinforcement of polypropylene with Phenylone stiff-chain fibers produces a composite with a high impact viscosity. Organoplastics based on polypropylene and aramid fibers have a low density and friction coefficient and high durability. Reinforcement of polypropylene with aramid (SVM) and glass fibers increases the technological properties of the composites. The glass-filled organoplastics developed can be used in instrument making, radio engineering, and machine building as antifriction and construction materials.Ukrainian State Chemical Technological University, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 106–110, January–February, 1996.     

A structural feature of the end region of a crack

The structure of the end regions of progressive cracks in polypropylene and polyethylene films with different supermolecular structures is examined. It is established that in the end region the opposite sides of the crack are connected by oriented polymer.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 741–742, July–August, 1968.     

Study of the stresses associated with the hot orientation of certain carbon-chain fibers

The process of hot orientation of Khlorin, polyacrylonitrile, and polypropylene fibers is investigated; the stresses associated with this process are determined. The possibility of determining the actual temperature in the orientation zone is demonstrated. The effect of the mobility of the macromolecules on the stresses is considered.Tashkent Institute of the Textile Industry. Translated from Mekhanika Polimerov, No. 2, pp. 372–374, March–April, 1972.     

Mechanism of the increase in strength and heat resistance of oriented polymeric materials modified by graft copolymerization with vinyl monomers

The mechanical properties and structures of oriented films and fibers composed of polyethylene, polymethyl methacrylate, and other amorphous and crystalline polymers modified by the synthesis of uniformly distributed graft and block copolymers of methyl methacrylate, acrylonitrile, vinylidene chloride and other monomers have been the subject of a comparative investigation. The effect of the grafted polymers on the molecular mobility, relaxation processes, and solubility of the materials is explained by reference to a universal physical "crosslinking" mechanism. A theory of the interrelation between the structure and physical properties of the materials, the nature of the polymers, and the grafting conditions is developed and used to analyze the experimental data on a broad range of systems.V. I. Lenin Belorussian State University, Minsk. Translated from Mekhanika Polimerov, No. 6, pp. 968–975, November–December, 1973.     

Theoretical and maximum attainable strength of various uniaxially oriented polymers (film,fibers)

The theoretical strength of various ideally oriented synthetic fibers was calculated. The calculation was based on an assumption that the rupture of polymers involves simultaneous breaking of molecular chains and pulling asunder the chain ends. The temperature-time dependence of the strength of fibers was analyzed and the maximum attainable strength of fibers of various kinds was calculated to show that it is 2–5 times higher than that recorded in practice. The main causes of the difference between the attainable and attained levels of strength are associated with imperfections of the supermolecular structure and an insufficient degree of orientation of materials of this kind. The principal means of obtaining high strength levels of synthetic fibers were discussed.Mekhanika Polimerov, Vol. 2, no. 6, pp. 845–856, 1966     

Peculiarities of the Electret State of Melt-Spun and Melt-Blown Fibrous Polypropylene Materials

The charge state of melt-spun and melt-blown polypropylene fibers is investigated. It is shown that the production of fibers by melt-spinning and melt-blowing technologies promotes the formation of a spontaneous polarization charge. Possible mechanisms of fiber polarization are analyzed. The influence of parameters of the melt-spinning technological process and forced electrization of fibers during their formation in stationary and alternating electric fields on the magnitude and stability of the electret charge is examined. It is established that the application of a corona discharge to fiber polarization is more efficient for the electret state formation.     

Strengthening of Polypropylene Strips by Orientational Stretching in Liquids

Data on the orientational stretching of polypropylene strips in process liquids serving as plasticizers of polypropylene are presented. Such a stretching allows one to avoid many complications characteristic of stretching in air and to increase the maximum stretch ratio significantly (up to 15). The stretching of strips is accompanied by changes in the crystalline structure of polypropylene and by transformation of the amorphous phase into a crystalline one. It is established that the specific strength of the orientationally stretched strips as a function of stretch ratio has a maximum. This is caused by the competing processes of macromolecule orientation in the stretching direction and the destruction of molecular bonds, which leads to the origination of microdamages in the strip surface layer and to a growing content of amorphous phase. It is shown that the extraction of process liquids from the stretched strips increases their specific strength by 20–30%.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 251–264, March–April, 2005.     

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.     

Viscoelastic jet drawn under conditions of heat exchange with the ambient medium

The effect of a constant or variable pull on a heated (cooled) viscoelastic jet is investigated. The problem is resolved into the subproblems of the extension of a viscoelastic rod and the motion determined by the rate of the process. The formation of polystyrene fibers is treated as an example.Mekhanika Polimerov, Vol. 4, No. 3, pp. 540–546, 1968     

Effect of the molecular weight of polystyrene on the viscosity of concentrated solutions

The viscosity of solutions of polystyrene of various molecular weights (from 1.04 · 10² to 3.8 · 10⁵) in a poor solvent (decalin) and a good solvent (ethylbenzene) has been measured at temperatures from 15 to 70°C over a broad range of shear stresses from 10² to 10⁶ dyne/cm². The nature of the solvent has a considerable influence on the critical molecular weight and the absolute value of the viscosities of the solutions over the entire range of molecular weights and on the form of the flow curves of decalin solutions of polystyrene as a function of temperature. The heat of activation of viscous flow increases with increase in molecular weight and shear stress on the interval 20–80°C. The results obtained are explained in terms of the effect of the molecular weight of the polymer, the nature of the solvent, stress and temperature on structure formation in the solution and on the orientation of the macromolecules and structures in the flow process.Ural Gor'kii State University, Sverdlovsk. Translated from Mekhanika Polimerov, No. 5, pp. 920–926, September–October, 1970.     

Bi-directional evolutionary topology optimization of geometrically nonlinear continuum structures with stress constraints

This paper proposes a design method to maximize the stiffness of geometrically nonlinear continuum structures subject to volume fraction and maximum von Mises stress constraints. An extended bi-directional evolutionary structural optimization (BESO) method is adopted in this paper. BESO method based on discrete variables can effectively avoid the well-known singularity problem in density-based methods with low density elements. The maximum von Mises stress is approximated by the p-norm global stress. By introducing one Lagrange multiplier, the objective of the traditional stiffness design is augmented with p-norm stress. The stiffness and p-norm stress are considered simultaneously by the Lagrange multiplier method. A heuristic method for determining the Lagrange multiplier is proposed in order to effectively constrain the structural maximum von Mises stress. The sensitivity information for designing variable updates is derived in detail by adjoint method. As for the highly nonlinear stress behavior, the updated scheme takes advantages from two filters respectively of the sensitivity and topology variables to improve convergence. Moreover, the filtered sensitivity numbers are combined with their historical sensitivity information to further stabilize the optimization process. The effectiveness of the proposed method is demonstrated by several benchmark design problems.     

Micromechanical investigation of osteons with crossed lamellae

A micromechanical investigation of osteons with crossed lamellae has shown that they can be regarded as orthogonally reinforced material. The stress-strain curve has a break at low stresses. This effect can be explained by reference to the mechanical behavior of orthogonally reinforced laminates. It is assumed that a stress concentration develops at the fiber-matrix interface in the lamellae with transverse fibers oriented at 90° to the direction of loading, and that microfractures can develop in the osteon before the proportionality limit of the fibers parallel to the loading axis is reached.Study No. 73.00430.04 of the Italian National Research Council. Paper presented at the First All-Union Conference on Engineering and Medical Biomechanics, Riga, October, 1975.Rome University. Translated from Mekhanika Polimerov, No. 4, pp. 669–673, July–August, 1975.     

Small deformations of oriented polymers

On the basis of a phenomenological analysis of the temperature dependence of the modulus of instantaneous elasticity and the stress relaxation process, it is suggested that in the region of small deformations there are no breakages of the macromolecules that might affect the elasto-relaxational behavior of highly oriented polymers (fibers) as in the region of large deformations. To judge from the values obtained for the energy constants, these properties are determined by the number of intermolecular bonds in the amorphous regions (modulus of instantaneous elasticity) and the physical events associated with the reorganization of these bonds and hindered rotation of the chain units (relaxation process).S. M. Kirov Leningrad Institute of Textiles and Light Industry. Translated from Mekhanika Polimerov, No. 6, pp. 976–980, November–December, 1971.     

An infrared spectroscopic study of the breakdown of polymers under load

It has been found that when a uniaxial tension is applied to highly oriented polymer films of polypropylene, polyvinyl alcohol, or polyethylene, an increase in the intensity of the absorption bands corresponding to the vibrations of the C=O carbonyl groups is observed. These groups are produced by the oxidation of the free radicals formed on the rupture of the chemical bonds under the influence of mechanical stress. The composition of the products has been studied, and their concentration has been estimated. Curves giving the accumulation of C=O groups with time at constant load and with increase in stress for a fixed period of time under load have been studied. It is suggested that the rate of accumulation of C=O groups in both cases is determined chiefly by the rate of rupture of the molecular chains under load.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 433–436, May–June 1970.     

Effect of combined extrusion parameters on mechanical properties of basalt fiber-reinforced plastics based on polypropylene

Basalt fibers are efficient reinforcing fillers for polypropylene because they increase both the mechanical and the tribotechnical properties of composites. Basalt fibers can compete with traditional fillers (glass and asbestos fibers) of polypropylene with respect to technological, economic, and toxic properties. The effect of technological parameters of producing polypropylene-based basalt fiber-reinforced plastics (BFRPs) by combined extrusion on their mechanical properties has been investigated. The extrusion temperature was found to be the main parameter determining the mechanical properties of the BFRPs. With temperature growth from 180 to 240°C, the residual length of the basalt fibers in the composite, as well as the adhesive strength of the polymer-fiber system, increased, while the composite defectiveness decreased. The tensile strength and elastic modulus increased from 35 to 42 MPa and 3.2 to 4.2 GPa, respectively. At the same time, the growth in composite solidity led to its higher brittleness. Thus, a higher temperature of extrusion allows us to produce materials which can be subjected to tensile and bending loads, while the materials produced at a lower temperature of extrusion are impact stable. The effect of the gap size between the extruder body and moving disks on the mechanical properties of the BFRPs is less significant than that of temperature. An increase of the gap size from 2 to 8 mm improves the impregnation quality of the fibers, but the extruder productivity diminishes. The possibility of controling the properties of reinforced polypropylene by varying the technological parameters of combined extrusion is shown. The polypropylene-based BFRPs produced by the proposed method surpass the properties of glass and asbestos fiber-reinforced plastics.Submitted to the 10th International Conference on Mechanics of Composite Materials (Riga, April 20–23, 1998).Ukrainian State University of Chemical Technology, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 6, pp. 845–850, November–December, 1997.     

Alkali-silica reaction expansions in high-performance and normal-strength cement grouts reinforced with steel and synthetic fibers

The role of brass-coated steel (BCS), hooked steel (HS), and polypropylene fibers in controlling the expansion and cracking in high-performance and normal-strength cement grouts is investigated. The grouts were prepared using the BCS, HS (from 0 to 2.0 vol.%), or polypropylene (from 0 to 0.30 vol.%) fibers. Standard prisms (25 × 25 × 300 mm³) were cast and cured for 40 days before subjecting to a special treatment to accelerate the alkali-silica reaction (ASR). Expansion measurements were taken for these prisms over an immersion period of up to 98 days, during which the extent of cracking was monitored. The results indicated a significant role of brass-coated and hooked steel fibers at volume fractions of 1.0 and 2.0% and polypropylene fibers at a volume fraction of 0.15% in reducing the expansion due to the ASR. The reduction in expansion of high-performance and normal-strength grouts was also dependent, in addition to the fiber type and content, on the duration of immersion of the grouts in a NaOH solution.Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 1, pp. 121– 130, January–February, 2005.     

Growth of arterial cracks in polymers subject to static and fatigue loading

The growth kinetics of artificial and natural cracks (the former arising from notches) are studied in viscose, di- and triacetyl cellulose, nitrocellulose, polymethylmethacrylate, polystyrene, polypropylene, and carpon films by a micro-motion-picture method over a wide temperature range under both static and cyclic (fatigue) loading. In all the cellulose materials studied, the time required to form the nuclei of visible cracks is much shorter than the total life of the sample. The initial rate of crack growth depends exponentially on the applied stress and test temperature, so that the equation for the growth rate of an arterial crack is analogous to the general life equation. The different ways in which stress and test temperature affect the parameters of the equation describing the kinetics of crack growth enable us to distinguish the effect of local heating and that of the relaxation processes in the fatigue problem.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 253–265, March–April, 1970.