Equilibrium Shapes of Pressure Vessel Domes in Asymmetric Winding

Errors in the programs of winding pressure vessels can lead to an asymmetric reinforcement structure, which affects the equilibrium shape of their domes and the tension in the left and right families of filaments. In this paper, equations determining the equilibrium shape of the domes, the tension in filaments, and the shear stresses between layers are obtained. Examples with winding trajectories in the form of geodesics and constant-deviation lines are considered. It is found that, for pressure vessels, in the absence of external torque, the tension levels in filaments of the left and right families differ considerably. It is also revealed that, for actual friction coefficients in winding, the shear stresses taken up by the binder are insignificant. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 6, pp. 743–752, November–December, 2005.     

A continuous model for investigation of physically nonlinear deformation of orthotropic sandwich plates

A phenomenological yield condition for quasi-brittle and plastic orthotropic materials with initial stresses is suggested. All components of the yield tensor are determined from experiments on uniaxial loading. The reliability estimates of the criterion suggested is discussed. For a plastic material without initial stresses, the given condition transforms into the Marin—Hu criterion. The defining equations of the deformation theory of plasticity with isotropic and “anisotropic” hardening, associated with the yield condition suggested, are obtained. These equations are used as the basis for a highly accurate nonclassical continuous model for nonlinear deformation of thick sandwich plates. The approximations with respect to the transverse coordinate take into account the flexural and nonflexural deformations in transverse shear and compression. The high-order approximations allow us to model the occurrence of layer delamination cracks by introducing thin nonrigid interlayers without violating the continuity concept of the theory. Submitted to the 11th International Conference on Mechanics of Composite Materials (Riga, June 11–15, 2000). Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. pp. 329–340, May–June, 2000.     

Correlation between the strength of fiber-reinforced plastics and the adhesive strength of fiber—Matrix joints

The relationship between the strength (σc) of unidirectional fiber-reinforced plastics in different stressed states and the interfacial strength of their components is investigated. The shear adhesive strength (τ0) of fiber—matrix joints determined by the pull-out technique is used as a measure of the interfacial strength. To obtain the correlation curves betweenσc andτ0, the experimental results are used, where both the plastic and adhesive strength change under the influence of a single factor. In this case, such factors are the fiber surface treatment, nature and composition of polymer matrices, and test temperature. It is shown that the strength of the glass, carbon, and boron plastics increases practically linearly with increased interfacial strength. Such a behavior is observed in any loading conditions (tension, shear, bending, and compression). Sometimes, a small (10–20%) increase in the adhesive strength induces a significant (50–70%) growth in the material strength. Therefore, the interface is the “weak link” in these composites. The shape of theσc—τ0 curves for composites based on the high-strength and high-modulus aramid fibers and different thermoreactive matrices depends on the nature of the fiber and the type of stress state. In many cases, the composite strength does not depend on the interfacial strength. Then, the fiber itself is the “weak link” in these composites. Submitted to the 11th International Conference on Mechanics of Composite Materials (Riga, June 11–15, 2000). Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 3, pp. 291–304, May–June, 2000.     

Spatial braiding of cylindrical articles

The effective deformative characteristics of spatially reinforced composites made by spatial braiding along the generatrices of a one-sheet hyperboloid are analyzed. The geometrical relationships determining the structure of a unit cell of a braided composite are derived. The effective thermoelastic characteristics are calculated by the method of orientational averaging. The dependences of the bending and torsional stiffnesses of thick-walled cylindrical rods — made by the method suggested and by winding — on the braiding/winding angle are compared. The numerical estimations are given for rods made of carbon (CFRP) and aramid (AFRP) epoxy plastics. Submitted to the 11th International Conference on Mechanics of Composite Materials (Riga, June 11–15, 2000). Translated from Mekhanika Kompzitnykh Materialov, Vol. 36, No. 3, pp. 341–354, May–June, 2000.     

Effect of fillers on the viscosity and viscoelasticity of low-density polyethylene melts. Communication 1

An investigation of low-density polyethylenes filled with up to 30% by volume dispersed particles, has shown that for both the matrix and the composites the apparent viscous flow activation energy does not depend on the shear stresses and increases starting from a certain filler concentration at which the conformation range in the matrix is depleted. The dependence of the relative viscosity of the compositions on the volume filler content is satisfactorily described by an equation that contains the reduced filler concentration, defined as the ratio of the nominal filler concentration to the limiting concentration at which the adsorption layers on the particles extend throughout the matrix. The thickness of the polymer layer adsorbed on the particles must be determined from the specific exterior particle surface, with allowance for the volume of the polymer in the sorption space of the porous filler.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 478–486, May–June, 1976.     

Strength and deformation characteristics of polymer blend films obtained from water systems

The relationship between the tensile strength and deformation characteristics, composition, and structural organization of films obtained by casting of two-component water-based system blends — a solution of the rigid partly crystalline polymer polyvinyl alcohol (PVA) and an emulsion of the compliant amorphous polymer polyvinyl acetate (PVAc) — has been investigated. The aim of this investigation was to ascertain the possibility of obtaining film materials with increased deformability based on the biodegradable PVA. The composition dependences of the initial modulus of elasticity, the maximum stress, yield stress, the ultimate strength, the ultimate strain, and of the unit work of fracture and other characteristics of films have been analyzed. An analysis of the tensile true stress–strain curves of systems with volume fractions of PVA less than 0.5 points to their considerable orientation strengthening upon tension.     

Multicriteria optimization of a rectangular composite plate subjected to longitudinal thermal stresses and buckling in shear loading

The multicriteria optimization of the structure and geometry of a laminated anisotropic composite plate subjected to thermal and shear loading is considered. From the known properties of the monolayer and given values of variable structural parameters, the thermoelastic properties of the layered composite are determined. The optimization criteria — the critical shear load and the longitudinal thermal stresses — depend on two variable design parameters of composite properties and temperature. In the space of optimization criteria, the domain of allowable solutions and the Pareto-optimal subregion are found. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 1, pp. 85–92, January–February, 2007.     

Residual stresses in plastic rings reinforced with glass and manufactured with consolidation of the various layers

The residual stresses in thin-wall plastic rings reinforced with glass and prepared by the method of consolidating the layers in combination with various winding regimes have been studied experimentally. It is shown that variation of the winding regime from one layer to another can change the distribution of the stresses through the thickness of the ring.Moscow Energy Institute. Translated from Mekhanika Polimerov, No. 1, pp. 174–176, January–February, 1972.     

Thermomechanical and adhesive properties of radiation-modified polymer composites for thermosetting products

Gamma-irradiated blends of polyethylene (PE) with ethylene-propylene-diene copolymer (EPDM) and a thermotropic liquid-crystalline polymer (LCP) are investigated at absorbed radiation doses not exceeding 150 kGy (10 kGy=1 Mrad). The temperature dependences of elastic moduli, tension diagrams at a temperature above the melting point of the crystalline phase of PE, and long-term strain recovery curves for oriented test specimens are presented. The kinetics of thermal relaxation and shrinkage stresses in previously oriented composite specimens upon their heating and cooling is investigated. Data on the influence of LCP additions on the adhesive interaction of the compositions with steel are obtained. The peculiarities of thermomechanical and adhesion properties of these composites are discussed taking into account the morphologic and calorimetric data obtained. Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 3, pp. 379–394, May–June, 2000.     

Compromise optimization of a rectangular composite plate subjected to biaxial thermal loading and buckling under the action of shear

The compromise optimization of the structure and geometry of a laminated anisotropic composite plate subjected to biaxial thermal shear loading is considered. From the known properties of the monolayer and given values of a variable structural parameter, the thermoelastic properties of the layered composite are determined. The optimization criteria — the critical shear load and the longitudinal and transverse thermal stresses — depend on two variable design parameters of composite properties and temperature. In the space of optimization criteria, the domain of allowable solutions and the Pareto-optimal subregion are found. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 4, pp. 471–478, July–August, 2008.     

Optimization of the injection molding process for short-fiber-reinforced composites

A fast and effective methodology integrating the finite-element and Taguchi methods is presented to determine the optimal design conditions of the injection molding process for short-fiber-reinforced polycarbonate composites. The finite-element-based flow simulation software, M-flow, was employed to simulate the molding process to obtain the fiber orientation distributions required. The Taguchi optimization technique was used to identify the optimal settings of injection molding parameters to maximize the shear layer thickness. The effects of four main parameters — the filling time, melt temperature, mold temperature, and injection speed — on the fiber orientation or the shear layer thickness were investigated and discussed. It is found that the dominant parameter is the filling time. The best levels of the four parameters to acquire the thickest shear layer are also identified.     

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.     

Programmed winding of glass-reinforced plastics

It is proposed to employ a variable winding tension designed to give a required initial stress distribution. The program is constructed on the basis of solutions describing the loss of tension associated with winding and the softening of the resin during heat treatment. The problems are solved in the elastic formulation. Programs are obtained for three cases: constant tension in a ring sill on the mandrel, compensation of the stresses that develop after removal from the mandrel, and compensation of the thermoelastic stresses that develop during cooling.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 48–53, January–February, 1970.     

Stability of a Circular Sandwich Ring under an Axially Symmetric Temperature Field Inhomogeneous across the Thickness

The linearized problems on the stability of a circular sandwich ring of symmetric structure under an axially symmetric temperature field inhomogeneous across the core thickness are stated and analytical solutions to them are given. The first problem deals with the mixed flexural buckling form (BF) of the ring as a whole, realized as a result of buckling in one of the load-carrying layers due to formation of precritical pressure stresses in the layer. The second problem considers purely shear BFs when one load-carrying layer is rotated relative to the other. The deformation processes for the load-carrying layers are described by the Kirchhoff-Love model, and for the core of arbitrary thickness - by two models, namely by the equations of the plane problem of elasticity theory and by the model of a transversely soft layer of arbitrary thickness (the same equations simplified by the assumption of zero circumferential normal stresses). Within the frames of the first model adopted for the core, the shear BF is theoretically possible but practically unrealizable, since the mixed flexural BF arises earlier than the shear BF.     

Conservation theorems for magnetic field and vorticity in two-dimensional conducting fluid flows

The classical conservation theorems for magnetic force lines, magnetic flux through a fluid surface, and intensity of magnetic vector tubes are generalized to plane flows of a finitely conducting fluid in an orthogonal magnetic field. The Helmholtz and Kelvin vorticity conservation theorems are generalized for plane motion of a viscous conducting fluid in an orthogonal magnetic field and the Bernoulli integral is derived. The Bernoulli integral is also generalized for plane motion of viscous ideally conducting fluid in a longitudinal magnetic field. Translated from Nelineinye Dinamicheskie Sistemy: Kachestvennyi Analiz i Upravlenie — Sbornik Trudov, No. 2, pp. 46–49, 1994.     

Effect of surface modification of fibers with a polymer coating on the interlaminar shear strength of a composite and the translation of fiber strength in an F-12 aramid/epoxy composite vessel

The surface of aramid fibers was modified with a polymer coating — a surface treatment reagent containing epoxy resin. The resulting fibers were examined by using NOL tests, hydroburst tests, and the scanning electron microscopy. The modified fibers had a rougher surface than the untreated ones. The interlaminar shear strength of an aramid-fiber-reinforced epoxy composite was highest when the concentration of polymer coating system was 5%. The translation of fiber strength in an aramid/epoxy composite vessel was improved by 8%. The mechanism of the surface treatment of fibers in improving the mechanical properties of aramid/epoxy composites is discussed. Russian translation publeshed in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 6, pp. 729–738, November–December, 2006.     

Experimental study of the effect of technological parameters on the residual stresses in thin-walled coiled parts

The effect of the parameters of heat treatment and programmed winding under tension on the residual stresses in thin-walled coiled parts made from glass plastic by the "dry" winding of a heated glass strip on an unheated mandrel is studied experimentally. The effect of the thickness of the parts on the maximum radial residual stresses is considered. A method is proposed for regulating the residual stresses in parts with very thick walls.Translated from Mekhanika Polimerov, No. 1, pp. 75–80, January–February, 1972.     

Moisture absorption and mechanical and acoustic responses in shear of a glass fiber fabric/epoxy resin composite

An analysis of the mechanical and acoustic responses of a laminate composed of 12 layers of glass fiber fabric/epoxy resin and conditioned in environments with relative humidities of 0, 60, and 96% RH at 60°C is presented. The first part of the study consists in following the weight gain according to the duration of hygrothermal conditioning, and the second part—in test ing 45°-oriented specimens in uniaxial tension up to failure at constant imposed displacement rates, with registrating the acoustic emission to track the damage process. The influence of moisture content in the material showed up as a significant decrease in its shear modulus, shear stress, and acoustic emission with growing quantity of absorbed water. An exponential function is proposed for describing the relationship between the varying shear modulus and the shear strain. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 43, No. 5, pp. 595–602, September–October, 2007.     

Yield condition for circular cylindrical shells made of a fiber-reinforced composite

A yield condition is obtained for circular cylindrical shells made of a definite class of fiber-reinforced composite material whose components possess plastic properties. It is shown that, in the plane of generalized stresses — the axial bending moment and the circumferential force (when the axial force is absent) — the yield curve consists of two linear and four curvilinear sections. By approximating the curvilinear sections, we get a piecewise linear yield condition described by a hexagon in the plane indicated. The nonlinear equations and the corresponding piecewise linear equations of the yield condition for particular cases are given in the form of tables. In solving specific boundary-value problems, we consider a circular cylindrical shell simply supported at its ends and loaded with a uniform internal pressure, for which the load-carrying capacity is determined in relation to the mechanical properties of composite components and some characteristic geometrical parameters. The results of numerical calculations are represented in the form of graphs. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 5, pp. 655–666, September–October, 2006.     

Biplastic pipes for high-pressure oil pipeline systems

A high-performance, corrosion-resistant biplastic pipe for high-pressure oil pipeline systems is presented. The pipe combines an outer load-carrying layer formed from unidirectionally glass-reinforced plastic (GRP) sublayers by wet multi-circuit winding and an inner sealing layer of high-density polyethylene. Both demountable and permanent joints, tees, and other parts are constructed for these pipes. The biplastic pipes ensure reliable operation of oil pipeline systems under a pressure of up to 200 bar. The experimental results and calculated estimates of the strength of biplastic pipes are presented. The results of using these pipes in oil pipeline systems in the Perm’ region are discussed. Presented at the 11th International Conference on Mechanics of Composite Materials (Riga, June 11–15, 2000). Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 3, pp. 407–418, 2000.