The relative expansion of polymer gels in uniaxial stretching

In the stretching of undried polyacrylonitrile fibers in the gel state, an increase in the cross sectional area, calculated from the diameter, is observed as compared with the cross sectional area obtained from the fact that the volume of the sample remains constant during stretching. The effect of relative expansion of polymer gels during the stretching process is explained by a delay in the relaxation processes, related to the orientation of amorphous sections and the rearrangement of the microstructure on a supermolecular level.All-Union Scientific-Research Institute of Synthetic Fibers, Kalinin. Translated from Mekhanika Polimerov, No. 5, pp. 927–929, September–October, 1972.     

Short-time strength of reinforced plastics in uniaxial compression

The short-time compressive strength of one-way and two-way reinforced plastics compressed in the direction of the axes of elastic symmetry has been theoretically and experimentally investigated with allowance for the mechanical properties of the components and the orientation of the fracture (shear) plane.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 621–628, July–August, 1969.     

Molecular orientation and the tensile strength of polystyrene

The tensile strengths of uniaxially oriented polystyrene films with molecular orientation determined by IR spectroscopy are compared. Two different orientation methods involving different time and temperature regimes are employed. It is found that the tensile strength is a unique function of the degree of orientation of the molecular segments of the polystyrene carbon chain irrespective of the means used to orient the specimens and increases linearly with increase in the degree of molecular orientation of the polymer. The experimental dependence is in satisfactory agreement with the results of a theoretical analysis.A. F. Ioffe Physico Technical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 4, pp. 612–615, July–August, 1969.     

Changes in the strength characteristics of human intervertebral disks under compression

Conclusions 1. The strength of intervertebral disks undergoes significant changes during the human lifetime. The data obtained allow the distinction of three periods: 1) a period of strength gain (newly born babies-18 years); 2) a stable period (20–40 years); and 3) a period of strength loss (from 50 to the death). The safety factor of strength of the intervertebral disks is the highest during the first two decades and decreases during the following age periods.2. The sex has a significant influence on the strength characteristics of the intervertebral disks.3. Changes in the limiting load of the intervertebral disks of the spine are characterized by a caudocranial gradient and the changes in the strength and the safety factor of strength, by a cranio-caudal gradient. The existing relationships do not depend on age or sex and reflect the significance of the functions of support and motion in different sections of the spinal column.4. The strength of the intervertebral disks depends on the degree of the degenerative-distrophic process, the mineral content of the tissues, the water content, and the ability of the disk tissues to retain water.S. V. Kurashov Kazan' State Medical Institute. Translated from Mekhanika Polimerov, No. 5, pp. 897–902, September–October, 1976.     

Characteristics of stretching of high-impact polystyrene and polycarbonate close to the glass transition temperature

A study has been made of the stress-strain characteristics of high-impact composites based on poly sty renes (PS) or polycarbonates (PC) in uniaxial stretching at temperatures close to the glass transition temperature of the matrix material Heterogeneity of the structure of the material at the microlevel, owing to the presence of a graft copolymer in the PS composites or the presence of polyethylene terephthalate (a reactive additive) in the PC, tends to lower the effective glass transition temperature as determined at high elongations. Weak interaction of the impact-strength modifiers with the matrix material (determining the heterogeneity of the structure at the macrolevel) results in a lower stability of uniform stretching in the region of the high-elastic state, but increases the values of the elongation at break in the transition region from the glassy state to the high-elastic state. From the standpoint of achieving high strength and deformability of high-impact composites during their processing, the structure should be organized so as to provide optimal heterogeneity at both the microlevel and macrolevel.Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 4, pp. 509–517, July–August, 1995.     

Elastic properties of microcomponents under uniaxial stress

In order to develop highly stressable microcomponents for various applications, the structural behavior of such parts has to be examined with respect to an accurate prediction of the elastic and plastic characteristics. When simulating microparts, the major challenge is to capture the significant material heterogeneities, which are the result of the small geometrical dimensions of the components being of the same order of magnitude as the grain size. For this reason, the concept of effective properties fails and apparent properties have to be considered. In this paper we examine the elastic properties of microspecimens made of gold. Therefore, various finite element simulations have been evaluated statistically in order to identify the characteristic parameters of the distribution. Polycrystals are modeled as a periodic Voronoi tesselation with a uniform distribution of crystal orientations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Deformability of expanded polystyrene under short-term compression

The results obtained in an experimental investigation of deformability of expanded polystyrene (EPS) under short-term compression are presented. The density of EPS varied from 13 to 28 kg/m³. The method of design of experiments was used to determine the elastic modulus and the ultimate strain (corresponding to the end of quasi-linear deformability) under compression stresses operating perpendicularly and parallel to the faces of EPS products. A graphical interpretation of the models is also presented. Based on the experimental data obtained, it was concluded that the expanded polystyrene was homogeneous in mutually perpendicular planes with respect to its deformability in compression. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 5, pp. 639–656, September–October, 2007.     

Viscoelastic properties of a silica-filled styrene-butadiene rubber under uniaxial tension

A model composite — a silica-filled styrene-butadiene rubber with a various filler volume content — was tested for creep and creep recovery at different tensile load levels to evaluate the effect of viscoelasticity on the deformational properties of filled rubbers. A constitutive equation describing the diagram of equilibrium deformation of the composite in quasi-static loading was obtained from an analysis of creep test results. The equation was common for the filled rubber at different filler content. The existence of such a curve has been confirmed by experimental unloading diagrams registered in cyclic loading-unloading tests. It is shown that the phenomenological equations obtained from an analysis of creep recovery test results can be used successfully for describing the hysteresis loops of second and subsequent cycles for cyclic tests with a constant maximum stretch ratio.     

Explicit energy-minimizers of incompressible elastic brittle bars under uniaxial extension

A rectangular bar made of a hyperelastic, but brittle, incompressible homogeneous and isotropic material is subject to uniaxial extension. We prove that the energy minimizers are, depending on the toughness coefficient of the material, either the homogeneous deformation, or the family of deformations for which a horizontal fracture breaks the material in two rectangular pieces, each of which is a rigid motion of the undeformed piece.     

Structural theory of the strength of reinforced plastics

Conclusions In the present study, we developed structural criteria that make it possible to predict at the component level (polymer binder, fibers) and interface level the long-term strength of laminated reinforced plastics in a plane stress state. The proposed relations make it possible to evaluate the effect of the rheological properties of the components, their volume fractions, and the geometry of the structure of the laminated packet on the long-term strength of reinforced plastics. The relations also permit resolution of the inverse problem: efficiently design the structure of such materials for specific loading conditions.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 833–839, September–October, 1989.     

Creep and aftereffect of polyethyleneterephthalate films under conditions of uniaxial stress

The results are given for an experimental investigation of creep and aftereffect in polyethyleneterephthalate films stressed in tension. It is shown that the creep is well represented by an exponential relation. A method of determining the corresponding coefficients is described.Mekhanika Polimerov, Vol. 1, No. 2, pp. 59–63, 1965     

Effect of electrical discharges on the mechanical strength and molecular weight of polystyrene film

Electrically aged polystyrene film was examined to determine the effect of voltage, aging time, and nature of the medium on the mechanical strength and molecular weight. It was established that the changes in the mechanical strength and molecular weight of the film always correspond.Mekhanika Polimerov, Vol. 4, No. 1, pp. 59–63, 1968