Lamellar structure and plasticity micromechanisms in bulk crystalline polymers. Communication 1

It is shown by electron microscopy that the lamellar structure typical of bulk crystalline polymers is identical in its structural-morphological characteristics with the typical products of martensite transformations in metal systems. It is also established that the polymer crystallization process has the typical characteristics of transformations governed by the shear (martensite) mechanism. These conclusions are used as a basis for an examination of the principal factors controlling the formation of the real structure of bulk polymers. The thermodynamic conditions under which bulk polymers crystallize require that the lamellar-spherulitic structure be formed in accordance with a self-consistent shear mechanism. In accordance with the new model, the spherulites represent an organization of the martensite lamellae in which the structural stress fields are mutually compensated. The proposed model underlines the fact that polycrystalline polymers and metal systems in the martensitic state are structurally similar materials.E. O. Paton Electrowelding Institute, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 3, pp. 387–394, May–June, 1976.     

Effect of production technology upon the supramolecular structure of crystalline polymers

The supramolecular structure and some other properties (density, microhardness) of high-density polyethylene and polycaprolactam specimens, molded under various conditions and aged for periods up to five months, have been studied.The change in the nature of the supramolecular structure and properties of the tested materials was determined in relation to molding conditions and aging time. It was found that the properties of these materials are determined by their supramolecular structure.Mekhanika Polimerov, Vol. 1, No. 2, pp. 9–14, 1965     

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.     

Kinetic theory of creep and lifetime of oriented crystalline polymers with allowance for supermolecular structure

A previously proposed model [7] is used as the basis for a study of the kinetics of failure under load of an amorphous-crystalline oriented polymer with allowance for the unequal length of the chains in the amorphous zone. A constant-load creep curve is constructed. An expression is given for the lifetime t of the specimen. The relation _mt = const, where _m is the steady-state creep rate, is proved. The kinetics of free radical concentration in time in a specimen under load are investigated. The results are compared with experimental data.Mekhanika Polimerov, Vol. 3, No. 1, pp. 8–18, 1967     

Elasticity and strength of nonoriented partially crystalline polymers

The dependence of the elastic modulus and strength on the crystallinity and temperature was studied. During the analysis of the strength data, the nonoriented crystalline polymers can be regarded as compositions consisting of a compliant matrix (amorphous phase) and a more rigid reinforcement (crystalline phase).The A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 964–968, November–December, 1975.     

Thermodynamic stability of crystalline polymers in the transition region

The type of phase transition can be determined from the temperature dependence of the coefficient (–P/av)_s and the stability determinant D. We have calculated these quantities for polyethylene from data on the speed of ultrasound, density, and the specific heat C_p.Krupskaya Moscow Regional Pedagogical Institute. Translated from Mekhanika Polimerov, No. 4, pp. 724–726, July–August, 1971.     

A molecular model of creep and stress relaxation in crystalline polymers

A possible model of defect formation in a polymer crystal lattice is considered. The results of an investigation of creep and stress relaxation in crystalline polymers are interpreted on the basis of the model proposed.T. G. Shevchenko Kiev State University. Translated from Mekhanika Polimerov, No. 6, pp. 969–975, November–December, 1971.     

Comparison of dilatant plasticity models in application to rubber-toughened polymers

The overall deformation behavior of rubber-toughened polymers (e.g. PC/ABS blends) exhibits a pronounced plastic dilatancy. As this volume increase results from diverse micromechanisms the appropriate structure of a macroscopic model is not obvious. In this contribution, different material models featuring plastic dilatancy are compared with regard to their ability to capture the deformation behavior of PC/ABS in different loading situations. All models are calibrated to match experimental data under uniaxial tension in terms of true stress-strain curves and the evolution of volume strain. Afterwards they are employed in finite element (FE) simulations of single-edge-notch-tensile (SENT) tests. Patterns of plastic deformation computed from the different material models are compared to experimental findings. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

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.     

Formation of crystalline bubble structure in wet metal foams

Small monodispersed bubbles form regular patterns when they agglomerate. Many experimental investigations revealed a preference of f.c.c. packing against h.c.p. packing in these structures, that could not yet be explained. In the present work this feature is reproduced numerically and analyzed. It is shown that drainage from layers above causes the preference. By investigating the transient crystal growth and packing rearrangement a mechanism is found that reduces the stability of h.c.p. packing and explains the phenomenom. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Supramolecular structure and incipient cracks in three-dimensional stitched amorphous polymers

The electron-microscopic method was used to study the structure of unsaturated polyester films. The initial submicrocracks developing in the loaded films were studies by the low-angle x-ray diffraction method. It is shown that for these polymers a typical feature is the globular structure with a globule diameter of 10³–3·10³ Å, and the transverse dimension of the submicrocracks developing under the action of a load practically coincides with the globule diameter.     

Theory of filled polymers and the problem of modifying the structure and properties of polymers with fillers

An attempt is made to explain the effect of fillers on the structure and properties of polymers. The effect of fillers on the state of thermodynamic equilibrium and the stability of polymer structure and properties is also considered.Kiev Shevchenko State University. Translated from Mekhanika Polimerov, No. 6, pp. 1031–1041, November–December, 1970.     

End defects in crystalline polyethylene. 1. Statement of the problem and modeling of the steric structure of end defects

Conclusions 1. Changes in the conformations of polyethylene molecules around the end of a neighboring chain and around the ends of two neighboring chains have been determined on an electronic calculator for various directions of end bending.2. It has been ascertained that a column of bivacancies disappears with simultaneous formation of spiral dislocations at smaller distances from the chain end to the crystallite surface than in the case of a single-vacancy column.3. Energies of formation of end defects and the bonding energy of defects upon aggregation have been calculated.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 400–407, May–June, 1978.     

Study of prefracture states of rigid polymers. 2. Elastic limit and strength

An explanation is offered for the relation between the magnitude of stresses at the elastic limit (strength) and the strains in rigid polymers. The possibility of high-elastic deformation and orienting processes, which have been considered in [1], is also explained here. Expressions are derived that relate the elastic limit to the strain, the modulus of elasticity, the coefficient of thermal expansion, and the Poisson ratio.For communication 1, see [1].A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 195–201, March–April, 1976.