Strength properties of oriented amorphous linear polymers in relation to their structure

Tensile tests have been conducted at room temperature on uniaxially oriented films of a number of amorphous linear polymers. It has been shown that the mechanical properties of the oriented polymers in the glassy state are chiefly determined by two parameters of the structure—the degree of orientation of the macromolecule segments and the concentration of stressed chains per unit volume, irrespective of the molecular weight of the polymer and the orientational stretching conditions.Mekhanika Polimerov, Vol. 3, No. 3, pp. 455–460, 1967     

Embryonic submicroscopic cracks in loaded polymers

The experimental work on embryonic fracture cracks in polymers recently carried out in the A. F. Ioffe Physico-Technical Institute, Academy of Sciences of the USSR, is reviewed. The cracks have been studied by diffraction methods, chiefly by small-angle x-ray scattering. A principal result of this research is the possibility of formulating the general principle of a micromechanics of polymer fracture. The theory is based on data on the behavior of submicrocracks in polymers (size, concentration), the structural conditions and molecular mechanism of crack formation, the enlargement of submicrocracks, their influence on microcrack formation, and the growth of the macrocracks.     

Relaxation processes in oriented amorphous polymers

Values of the birefringence and high-elastic strain are presented for amorphous polystyrene subjected to stretching and annealing. The laws of the relaxation processes that occur in linear polymers under these conditions are discussed.Mekhanika Polimerov, Vol. 2, No. 3, pp. 323–329, 1966     

Modelling structural recovery in amorphous polymers

Constitutive equations are derived for linear viscoelastic response and enthalpy relaxation in amorphous polymers in the vicinity of the glass transition temperature. According to the concept of cooperative relaxation, a glassy polymer is treated as an ensemble of weakly-connected relaxing regions. Mechanical relaxation in a region occurs when the thermally activated flow unit reaches some liquid-like state. Structural recovery is modeled as a sequence of hops in which rearranging regions change their traps. A constitutive model for the linear viscoelastic behavior and enthalpy relaxation in a glassy polymer is validated using experimental data in mechanical and calorimetric tests on polycarbonate and poly (methyl methacrylate). Fair agreement is demonstrated between observations and results of numerical simulation.     

Investigation of self-healing of cracks in polymers

A method is worked out for studying the process of self-healing of cracks in polymers. The criterion of self-healing of a crack — the degree of self-healing — is found, and its temperature dependence is determined. It is shown that a change of the relaxation spectrum of a polymer affects the process of self-healing occurring at the tip of a crack.Deceased.L. Ya. Karpov Physicochemical Scientific-Research Institute. Translated from Mekhanika Polimerov, No. 2, pp. 271–275, March–April, 1970.     

Investigation of self-healing of cracks in polymers

The effect of the molecular weight of a polymer and the environment on self-healing of cracks in polyvinyl acetate was investigated. It was confirmed that any change of the relaxation spectrum of the polymer affects the self-healing process occurring at the crack tip.See [1] for report 1.Deceased.L. Ya. Karpov Scientific-Research Physicochemical Institute, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 445–448, May–June, 1970.     

Relaxation processes in oriented amorphous and crystalline polymers

Studies were made of the experimental data on the relaxation processes leading to the preferential molecular disorientation and uniaxially drawn amorphous and crystalline polymers.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 787–792, September–October, 1972.     

Deformations and stresses around submicroscopic cracks in loaded polymers

Structure deformations upon loading of oriented films of polycaproamide (Kapron) or polypropylene when submicroscopic cracks (dimensions of hundreds of Ångstroms) have appeared in the samples in high concentration (up to 2 · 10¹⁵ cm^–3) have been studied by x-ray diffraction methods at low and large angles. It has been established that the appearance of submicro-cracks causes relieving of the regions adjacent to them along the loading axis (extent about 1000 Å) and an increase in stress in the lateral zone relative to the crack, which is manifested in an intensification of the stretching of these zones.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 51–58, January–February, 1972.     

Investigation of the self-healing of cracks in polymers

The effect of the medium and the thickness of the polymer film on the self-healing of cracks in polyvinyl acetate has been investigated. The medium in which the specimen "recovers" may either facilitate or impede the self-diffusion of macromolecules and other structural units in the contact zone formed by the closing of the edges of the crack. The "recovery" coefficient decreases when healing takes place in the presence of the vapor of a surface-active agent and increases under conditions such that water molecules are desorbed from the surfaces of the crack; transition from a thick to a thin layer of polymer slows the self-healing process as a result of the reduced mobility of the kinetic units.For communication 2 see [2].Deceased.Karpov Scientific-Research Physicochemical Institute, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1110–1113, November–December, 1970.     

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.     

Self-adhesion of amorphous polymers and their miscible blends

The amorphous film surfaces of polystyrene (PS), poly(2,6-dimethyl 1,4-phenylene oxide) (PPO), and their miscible blends are brought into overlap contact below the glass transition temperature T _g for 10 min and 24 h in order to obtain PS—PS, PPO—PPO, and blend—blend self-adhesive joints. It is shown that after the contact of the blend surfaces, i.e., when the molecules of both PS and PPO are present at the interface, it is possible to attain higher values of shear strength as compared with those at PS—PS and PPO—PPO interfaces. This points to the contribution of a specific interaction between the segments of PS and PPO to the strength development at the interface. Submitted to the 11th International Conference on Mechanics of Composite Materials (Riga, June 11–15, 2000). Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 1, pp. 127–135, 2000.     

Determination of the parameters of the reticulate structure of amorphous linear polymers subjected to orientational stretching

As a result of interlacing the macromolecules in linear block polymers form a sort of molecular network. The structure of this network affects the strength characteristics of oriented amorphous linear polymers in the brittle state. An important characteristic of the reticulate structure is the number of network chains per unit volume. The literature describes a method of determining this quantity based on the degree of stretching and the stress developed during stretching of the softened polymer. This method is not sufficiently accurate, since it disregards the presence in linear pclymers of network nodes of different stability. The proposed method of calculating this quantity is based on an analysis of the "equilibrium contraction" curves and takes into account the relaxation processes in the polymers. It is more accurate than that previously employed.Mekhanika Polimerov, Vol. 2, No. 2, pp. 163–169, 1966     

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.     

Boundary equations in nonstationary diffraction problems for elastic waves on three-dimensional cracks

Translated from Matematicheskie Zametki, Vol. 51, No. 4, pp. 119–123, April, 1992.     

Supermolecular structure and properties of polymers

Questions relating to methods of obtaining supermolecular structures and their effect on the properties of polymers are considered.Presented at 2nd All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1971.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 409–415, May–June, 1972.     

Modeling the finite strain deformation and initial anisotropy of amorphous thermoplastic polymers

This work deals with modeling the mechanical behavior of thermoplastic polymers in the finite strain regime over a wide range of temperatures. Thereby, special emphasis is put on the incorporation of an initial anisotropy in terms of “frozen-in” molecular orientation which results from a preceding manufacturing process. A computational example is discussed which considers an injection molded plate undergoing inhomogeneous deformation (buckling) during re-heating. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Finite thermo-viscoplasticity of amorphous glassy polymers: Experiments,modeling and simulations

The contribution is concerned with experimental procedures, constitutive modeling and the numerical simulations of finite thermo-viscoplastic behavior of glassy polymers. The experimental study involves both homogeneous and inhomogeneous tests at different temperatures under isothermal conditions. The true stress-true strain curves obtained from compressive homogeneous uniaxial and plane strain experiments are employed in the identification of adjustable material parameters. In contrast to the existing kinematic approaches to finite plasticity of glassy polymers, we propose a distinct kinematic framework constructed in the logarithmic strain space. This leads us to an algorithmically very attractive, additive kinematic structure in R⁶ similar to the geometrically linear theory. The proposed three-dimensional model is implemented into a finite element code. The load-displacement curves acquired from inhomogeneous experiments are compared against the results obtained from finite element analyses where the material parameters identified from homogeneous experiments are used. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mechanics of the static tension of a through chain in amorphous crystalline polymers

The displacements and tensions of the points on a through chain lying inside one crystallite of an oriented amorphous crystalline polymer are analyzed theoretically for various degrees of withdrawal of the chain from the crystallite. The tension of the chain in the amorphous region is examined as a function of its contour length and the length of the amorphous region. The nature and efficiency of the stoppers (obstacles) retaining the through chain inside the crystallites are considered. Specific results are calculated for polyethylene and polypropylene.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 771–778, September–October, 1973.