Molecular mechanism of oriented crystalline polymers

It is shown with reference to linear polyethylene that the deformation of an oriented crystalline polymer takes place as a result of elongation of the coiled parts of the macromolecules in the amorphous zones owing to conversion of gauche into extended trans isomers. The decrease in coiled isomer content when the specimen is deformed by approximately 5% is accompanied by a small number of chemical bond breakages. Repeat deformation by the same amount does not result in any additional breakage of polymer chains.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of The USSR, Leningrad. Translated from Mekhanika Polimerov, No. 4, pp. 584–588, July–August, 1973.     

Relation between the elastic deformation of oriented specimens of crystalline polymers and the "large-period" deformation

Illustrative calculations for a specific model of the supermolecular organization of an oriented crystalline polymer are presented as an explanation of the fact that the "large-period" deformation may exceed the macrodeformation of the specimen.Institute of High-Molecular-Weight Compounds, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 4, pp. 579–583, July–August, 1973.     

Elasticity of the intercrystallite zones and the mechanical properties of oriented polymers

As a result of a study of the behavior under load of the elements of the supermolecular structure of oriented amorphous-crystalline polymers it is shown that the stresses on the crystallites and the amorphous zones in series with them in the direction of the chain axes are equal to the mean stress applied to the specimen along the orientation axis. The nature of the elasticity and deformability of the amorphous zones is analyzed. A relation is obtained between the strength properties of oriented polymers and the number of load-carrying chains in the amorphous zones.Ioffe Physico-Technical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 1002–1007, November–December, 1969.     

Investigation of the energy effects accompanying the elastic deformation of uniaxially oriented crystalline polymers

The energy (thermal and mechanical) effects accompanying the elastic deformation of uniaxially oriented crystalline polymers have been investigated; it has been established that, when these polymers are stretched, heat is released. It is shown that the heat release in uniaxial tension is a consequence of localization of the elastic deformation in the poorly ordered regions of the polymer. The relation between the thermoelasticity of uniaxially oriented crystalline polymers and their supermolecular structure is examined.Institute of Heteroorganic Compounds, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 785–798, September–October, 1970.     

Some laws of the elastic properties of oriented fibrous polymers and fibers

The author considers the results of calculations of the limiting values of the elastic properties (modulus of elasticity and load-extension diagram) of the main types of chemical fibers, using a model with "ideal orientation" of the molecules and the derived laws of deformation of polymer chains. A method is proposed for calculating the elastic properties of "ideally oriented" polymers from the velocity of propagation of an elastic deformation pulse and the effective density of the "skeletons" of the polymer chains. Values of the moduli of elasticity of the amorphous regions of the structure of oriented polymers are calculated. The calculated results are compared with experimental data on the elastic properties of fibers.Mekhanika Polimerov, Vol. 2, No. 1, pp. 34–42, 1966Paper read at the XIV All-Union Conference on High-Molecular Compounds, Oriented State.     

Effect of gamma radiation on the mechanical properties of polyvinylidene fluoride

The variation of the strength and relative elongation at break with radiation dose has been investigated for unoriented block specimens of PVF₂ and for oriented specimens with different crystalline structure ( and ). A certain difference is observed in the behavior of the irradiated oriented specimens and an important difference in the behavior of oriented and unoriented specimens of PVF₂ with the same crystalline structure (). On the basis of the data obtained and the results of a study of the crystalline and supermolecular structure of the irradiated PVF₂ specimens it is concluded that there is a difference in the state of the amorphous regions in the oriented and unoriented PVF₂.Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 146–149, January–February, 1973.     

Time-temperature superposition. Review

Experimental attempts to confirm the applicability of time-temperature superposition as a means of predicting the deformation of polymeric materials are reviewed. Examples of the use of the method for the accelerated testing of amorphous and crystalline thermoplastics, thermosets, and composites are presented. The review is confined to the class of thermorheologically simple bodies and isothermal deformation regimes.     

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.     

Changes in the fine structure of polycaprolactam induced by hydrostatic pressure

The effect of high (up to 22,000 atm) hydrostatic pressure on the interplanar spacings and corresponding diffraction maxima in polycaprolactam has been investigated. The observations are interpreted in terms of the compressibility anisotropy relative to the amorphous and crystalline regions of the polymer and possible elastic deformation of the amorphous zones leading to tensile stresses in the crystalline regions that relax as the polymer ages owing to processes associated with changes in the conformations of the macromolecules and the number of crosslinks between segments.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 579–585, July–August, 1968.     

Effective elastic properties of 3D polypropylene microstructures of an injection moulded plate via different homogenization schemes

The mechanical properties of a polypropylene (PP) part depend on its morphology and degree of crystallinity. To evaluate its effective elastic behaviour two upscaling schemes are developed and compared. In the 1^st method the spherulites are assumed to be isotropic and vary linearly with the spherulite diameter. In the 2^nd one, the homogenization is performed successively on two scales. At the nanoscale, the bilamina of amorphous and crystalline phases is homogenized. Then, at the microscale, a 3D radial distribution of effective bilamina is homogenized. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Small finite deformations of an amorphous polymer material

Small finite deformations of a polymer material are considered. It is assumed that the volume of the specimen is conserved during deformation and that the strains are affine; furthermore, the equilibrium distance between network nodes is not equal to zero in the specimen, and the unit cell of the network is cubic. Various types of deformation are considered. The expressions obtained are compared with the results of the theory of high elasticity and the experimental data.Branch Institute of Chemical Physics, AS USSR, Moscow. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 997–1001, November–December, 1968.     

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.     

Thermomechanical behavior of liquid-crystal polyesters

We have used the thermomechanical method to investigate the processes of self-elongation and shrinkage in uniaxially oriented liquid-crystal (LC) polyesters (CPET — the copolyester of terephthalic acid, phenylhydroquinone, and p-hydroxybenzoic acid; Ultrax — the copolyester of terephthalic acid, isophthalic acid, and bisphenol) and the injection-molded copolyester of hydroxybenzoic and hydroxynaphthoic acids Vectra A900. A universal tensile tester and a thermomechanical tester were used for the investigations. We studied the deformation behavior for the first and second heating under negligible applied stress. We prepared CPET samples in the form of as-spun and annealed fibers, Vectra samples in the form of cubes cut from the nonoriented part of the molded piece (VI) and from the longitudinally oriented central part (VII), Ultrax samples in the form of strands (noncrystalline UI and crystalline UII). We observed a permanent length increase for the as-spun CPET (Fig. 1) and shrinkage in the glass-transition region for the annealed CPET (Fig. 2) for the first and second heating. Note that the as-spun CPET is a smectic polymer, and the annealed CPET contains smectic and crystalline phases. The thermomechanical curves of VI seem to be typical of any molded polymer (Fig. 3). In contrast, for the oriented VII we see spontaneous elongation upon heating in the direction of orientation, with pronounced transverse shrinkage (Fig. 4). The length increase for the noncrystalline UI is quite considerable for the first heating. We observed both spontaneous elongation below the glass-transition temperature and subsequent shrinkage for crystalline UII for the first heating. All the Ultrax curves are much smoother for the second heating (Fig. 5). Spontaneous elongation upon heating appears to be a characteristic feature of oriented LC polymers, the polymer being either fully oriented or oriented within some part of the sample. Shrinkage of LC polyesters upon heating is also possible, as a result of both processing factors and crystallinity. There are two types of restructurization processes: orientation and crystallization (possible for LC polymers capable of forming a crystalline phase).A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 32, No. 1, pp. 98–105, January–February, 1996.     

Relation between deformation and rotational isomerism

In uniaxially oriented polyethylene and polyethylene terephthalate films conformational transitions were studied by the absorption IR-spectroscopy method during deformation of the specimens carried to rupture in a wide range of temperatures and with different loading methods. It is shown that upon elongation of the polymers the concentration of trans isomers increases and that of gauche isomers decreases. A linear unique relation is obtained between the number of rotational isomers and magnitude of deformation in the amorphous parts of the investigated polymers. It is hypothesized that the conformational transitions determine the magnitude of deformation of amorphous-crystal-line polymers.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 1077–1080, November–December, 1975.     

A nanocomposite based on a styrene-acrylate copolymer and native montmorillonite clay 2. Modeling the elastic properties

A variant of stepwise determination of the elastic characteristics of quasi-isotropic polymer-silicate nanocomposites with randomly oriented platelike filler particles is considered. First, the elastic constants of transversely isotropic structural elements with coplanarly placed filler particles are obtained, and then they are averaged over all spatial directions by using the orientational averaging method. The characteristic features of the hierarchical structure of exfoliated and intercalated nanocomposites are also considered. The concentration dependences of elastic constants of a nanocomposite based on a styrene-acrylate copolymer and native montmorillonite clay are modeled, and the results obtained are compared with experimental data. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 2, pp. 235–246, March–April, 2006.     

Changes in the structure of polymeric materials in a magnetic field

It is shown that the action of a magnetic field leads to a change in the supermolecular structure of crystalline polymers. The creation of an oriented state in amorphous thermoplastics and thermosets is accompanied by an increase in their hardness and the homogeneity of the structural state.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 737–739, July–August, 1973.     

Deformation of composites with arbitrarily oriented orthotropic fibers under matrix microdamages

In the present work, a model of nonlinear deformation of stochastic composites under microdamaging is developed for the case of a composite with orthotropic inclusions, when microdefects are accumulated in the matrix. The composite is treated as an isotropic matrix strengthened by triaxial arbitrarily oriented ellipsoidal inclusions with orthotropic symmetry of the elastic properties. It is assumed that the process of loading leads to accumulation of damage in the matrix. Fractured microvolumes are modeled by a system of randomly distributed quasispherical pores. The porosity balance equation and relations for determining the effective elastic modules in the case of orthotropic components are taken as basic relations. The fracture criterion is specified as the limiting value of the intensity of average shear stresses acting in the intact part of the material. On the basis of the analytic and numerical approach, we propose an algorithm for the determination of nonlinear deformation properties of the investigated material. The nonlinearity of composite deformations is caused by the finiteness of deformations. By using the numerical solution, the nonlinear stress–strain diagrams are predicted and discussed for an orthotropic composite material for various cases of orientation of inclusions in the matrix.     

Application of the reduced concentration principle to filled polymers

An investigation has been made into the applicability of the reduced concentration principle to composites based on a partially crystalline polymer — low-density polyethylene — with 13 mineral fillers of different chemical composition, particle size, and porosity. It is shown that over the entire accessible interval of filler load factors the composites investigated obey the law of corresponding states. It is suggested that the deviation of the generalized dependence of the modulus of elasticity from the analogous dependence obtained for amorphous network polymers is associated with a decrease in the crystallinity of the polymer matrix with increase in filler concentration.     

横观各向同性多孔超弹性矩形板的单向拉伸

利用横观各向同性超弹性材料的广义neo-Hookean应变能函数研究了含有多个微孔的超弹性矩形板在单向拉伸作用下的有限变形和受力分析.给出了含有某种对称性分布的多个微孔的矩形板的变形模式,通过求解该变形模式满足的微分方程,将它用两个参数表示出来.可应用最小势能原理导出变分近似解,从而得到矩形板的变形和应力分布的解析解.分析了板中微孔的增长及微孔边缘应力的分布情况,讨论了板的各向异性程度及微孔的大小和孔间距离的影响,得到了单个、三个及五个微孔板中微孔的增长变形和孔边应力分布的一些基本规律规律,并进行了相互比较.     

Higher-Order Asymptotic Approximations for Surface Love Waves of SH Type in Tranversely Isotropic Elastic Media

A uniform asymptotics of the surface Love modes for a special case of anisotropy (tranverse isotropy) of an elastic media is obtained. In constructing the asymptotics of surface waves, the space-time (ST) ray method is employed. The wave field of each Love mode is represented as the sum of the ST caustic expansion involving the Airy functions with a real eikonal and two correction terms that are ST ray solutions, which in fact are inhomogeneous waves with complex eikonals. The eikonals and coefficients of the caustic and ray series are sought in the form of expansions in powers of two variables. The first variable is the distance from the surface, whereas the other characterizes the proximity of the caustic of a ray field to the boundary surface. Thanks to the specific structure of the elasticity tensor for a transversely isotropic medium, the boundary surface is necessarily a plane. A recursion process of computation of higher terms of the asymptotic expansion allows one to trace the conversion of the formulas obtained to the known ray solutions for isotropic elastic media. Relations between the elasticity parameters of a medium are obtained that ensure the existence of SH Love waves in a transversely isotropic medium and that are consistent with the conditions of the positiveness of the elastic energy of deformation. Bibliography: 6 titles.