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Mechanics of Composite Materials (v.40, #3)

Comparison of Mechanical Properties and Effects in Micro- and Nanocomposites with Carbon Fillers (Carbon Microfibers, Graphite Microwhiskers, and Carbon Nanotubes) by I. A. Guz'; Ya. Ya. Rushchitskii (pp. 179-190).
The mechanical properties and effects in fibrous composite materials are compared. The materials are based on the same matrix (EPON-828 epoxy resin) and differ in the type of fibers: Thornel-300 carbon microfibers, graphite microwhiskers, carbon zigzag nanotubes, and carbon chiral nanotubes. Two material models are considered: a model of elastic medium (macrolevel model) and a model of elastic mixture (micro-nanolevel model). Mechanical constants of 40 materials (4 types + 10 modifications) are calculated and compared. The theoretical ultimate compression strength along the fibers is discussed. The effects accompanying the propagation of longitudinal waves in the fiber direction are investigated.

Keywords: micro- and nanocomposites; mechanical properties; wave effects; Thornel fibers; graphite whiskers; carbon nanotubes

Stress Distribution in an Elastic Body with a Periodically Curved Row of Fibers by S. D. Akbarov; R. Kosker; Y. Ucan (pp. 191-202).
Within the framework of a piecewise homogeneous body model, with the use of exact three-dimensional equations of elasticity theory for anisotropic bodies, a method is developed for investigating the stress distribution in an infinite elastic matrix containing a periodically curved row of cophasal fibers. It is assumed that fiber materials are the same and fiber midlines lie in the same plane. The self-balanced stresses arising in the interphase in uniaxial loading the composite along the fibers are investigated. The influences of problem parameters on these stresses are analyzed. The corresponding numerical results are presented.

Keywords: unidirectional fibrous composite; curved fibers; row of fibers; self-balanced stresses

Stress-Strain State of a Cylindrical Sandwich Shell in an Axisymmetric Temperature Field Inhomogeneous across the Thickness by V. N. Paimushin; V. A. Ivanov; S. A. Lukankin; A. A. Bushkov (pp. 203-216).
Exact analytical solutions to the problems on the formation of an axisymmetric stress-strain state (SSS) in a circular cylindrical sandwich shell under the action of a temperature field inhomogeneous across its thickness are obtained. It is assumed that the end cross sections of the upper load-carrying layer are immobile in the axial direction, whereas those of the lower load-carrying layer are free. By virtue of the small relative thickness, the outer layers are assumed momentless. The transversely soft filler has an arbitrary thickness, and its SSS is described by equations of thermoelasticity simplified according to the model accepted for it. The boundary conditions stated for the transverse (radial) direction at shell ends correspond either to a free edge or to the presence of a diaphragm.

Keywords: cylindrical sandwich shell; transversely soft core; thermoelasticity; inhomogeneous across-the-thickness temperature field; analytical solution; stress-strain state

Room- and Low-Temperature Deformation of Multilayered Fiberglass Plastics Reinforced with a Fabric of Sateen Weave by N. K. Kucher; A. Z. Dveyrin; M. N. Zarazovskii; M. P. Zemtsov (pp. 217-226).
The regularities of elastic deformation of multilayered fiberglass plastics reinforced with a fabric of sateen weave are studied. The effect of cooling to 77 K on the averaged elastic characteristics of the orthotropic material is analyzed. The efficiency of mathematical modeling in calculating the stiffness and compliance parameters of the woven composites based on the geometry and mechanical properties of their constituents is investigated.

Keywords: glass-fiber-reinforced plastic; reinforcing fiber; sateen; deformation; low temperatures

Lamb Problem for a Half-Space Covered with a Two-Axially Prestretched Layer by I. Emiroglu; F. Tasci; S. D. Akbarov (pp. 227-236).
Within the framework of a piecewise homogeneous body model, with the use of the three-dimensional linearized theory of elastic waves in initially stressed bodies, an approach for investigating the Lamb problem for a half-space covered with a layer is developed. It is assumed that the half-space and the cover layer have two-axial initial stresses operating parallel to the layer plane. To the free face of the layer, a normal point force changing harmonically with time is applied. For solving the corresponding boundary value problems, the double-exponential Fourier transformation is employed. An algorithm for obtaining numerical results is proposed, which is examined in particular cases. Numerical results for the influence of prestretching the cover layer on the interfacial stresses are presented.

Keywords: prestretching; Lamb problem; two-axial initial stresses; cover layer; half-space

Design and Fabrication of Composite Smart Structures with High Electric and Mechanical Performances for Future Mobile Communication by C. S. You; W. Hwang (pp. 237-246).
In this paper, we have developed a load-bearing outer skin for antennas, which is termed a composite smart structure (CSS). The CSS is a multilayer composite sandwich structure in which antenna layers are inserted. A direct-feed stacked patch antenna is considered. A design procedure including the structure design, material selection, and design of antenna elements in order to obtain high electric and mechanical performances is presented. An optimized honeycomb thickness is selected for efficient radiation and impedance characteristics. High gain conditions can be obtained by placing the outer facesheet in the resonance position, which is at about a half wavelength distance from the ground plane. The measured electrical performances show that the CSS has a great bandwidth (over 10%) and a higher gain than an antenna without a facesheet and has excellent mechanical performances, owing to the composite laminates and honeycomb cores. The CSS concept can be extended to give a useful guide for manufacturers of structural body panels and for antenna designers.

Keywords: smart structures; sandwich structures; microstrip antenna; composite laminate; Nomex honeycomb

Deformational Properties of Irradiated Composite Materials Based on PET and PE by R. Merijs Meri; I. Jablonskis; J. Zicans; M. Kalnins; A. K. Bledzki (pp. 247-252).
Considering the wide applicability of polymeric composite materials, heterogeneous blends of poly(ethylene terephtalate) (PET) and polyethylenes of high and low densities (HDPE and LDPE, respectively) were investigated. Rheological (the flow-behavior index), mechanical (the yield strength and the Charpy impact strength), and morphological (crystallinity and the melting temperature) properties were detected for individual blend components and different blend compositions. A radiation treatment (γ-rays) was applied to improve certain characteristics of the heterogeneous blends. The results of this investigation show that the radiation modification can be successfully used to improve some physical properties of the PET-based blends and to choose individual blend components, optimum irradiation conditions, and desirable blend compositions, which allows producing materials with a predictable set of mechanical properties.

Keywords: poly(ethylene terephtalate); polyethylene; heterogeneous blends; flow-behavior index; yield strength; impact strength; compatibility factor; crystallinity

Analysis of the Adhesion and Adhesion Strength of Two-Layer Polymer Films and Coatings by A. Kviklys; I. Lukosiute (pp. 253-258).
The formation of adhesion bonds during the creation of two-layer polymer films and coatings capable of acid–base interaction is considered. The coatings are obtained from polymer solutions, and the second layer is formed from the polymer solutions and their mixtures on a hard polymer coating. As a result of absorption by the coating of a considerable amount of solvents (to 14%), polymer macrochains are able to approach one another at a distance necessary for the formation of acid–base (hydrogen) bonds and a transition layer. The polar component of the work of adhesion is equal to about 50% of the whole work W a. There is no interrelation of the thermodynamic work W a between the films and the work of their separation into layers. The main part of the external work upon the separation is spent (if strong donor–acceptor bonds are formed) for extracting the segments and macrochains of polymers out of the films.

Keywords: polymers; surface energy; two-layer films; work of adhesion; separation into layers

Structure and Properties of Electrodeposited Composite Metal–Nanodisperse Inorganic Compound Coatings by I. Vitina; J. Grabis; I. Zalite; V. Belmane; V. Rubene (pp. 259-268).
By using the electrodeposition method, composite Sn-inorganic coatings have been obtained. As the inorganic compounds, ultrafine PbMo6S8, NbCxNy, TixNy, and Ti0.63Nb0.34C0.38N0.58 powders were utilized. The Sn–PbMo6S8 coatings containing 28-88 wt.% PbMo6S8 were superconductive. The highly electroconductive Sn–NbCxNy coatings containing 1-88 wt.% of the disperse phase and the Sn–TixNy coatings with 42-70 wt.% TixNy were structurally stable at a low temperature (−50°C), solderable, and corrosion resistant on copper. The formation of the structure of the coatings is determined by the electrolyte composition, the cathode current density during the electrolysis, and the codeposition of the disperse phase. By electrodeposition of the chromium carbonitride Cr3C1.6N0.4, in the presence of H4P2O7 in an CrO3-based electrolyte, mat composite Cr–Cr3C1.6N0.4 coatings with 6.8 wt.% Cr3C1.6N0.4 were obtained, which had a finely uneaven surface structure. Such surfaces are needed in the cases where lubricants are used.

Keywords: composite coatings; electrodeposition; structure; superconductivity; corrosion resistance; solderability

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