Papers by Keyword: Elasticity

Abstract: The development and fabrication of novel composite materials requires accurate investigation of their mechanical properties. Although various approaches are well-established for investigation of linear elastic properties, there are only few methods that can be applied for study of nonlinear ones. In this report we describe and compare the performance of two different experimental approaches aimed for investigation of nonlinear elastic properties of glassy polymers and polymer-based composites.

Abstract: The problem of harmonic oscillations in electro-electromagnetic composites is studied. Oscillations can be initiated by the extended load vector, including the horizontal and vertical components of mechanical displacements, and electrical induction distributed on top of the surface. Boundary conditions assume full mechanical coupling for all layers of the structure. Electrical conditions on the surface top can be both electrically open, and electrically shorted. Magnetic conditions are similar to electric ones and describe the continuity of fields in between two mediums, or indicate the isolation of the magnetic field between them. The Green's function of electro–magneto–elastic medium is constructed. Phase velocities are obtained for various geometric proportions and materials.

Abstract: The article deals with the axisymmetric elastoplastic problem for a hollow thick-walled cylinder (plane deformed state), loaded from the inside and outside by uniform pressures proportional to one parameter. The material is considered to be perfectly plastic, with the elastic modulus and yield strength generally are arbitrary functions of the radius. In addition, the material is considered to be incompressible in both plastic and elastic zones. On the basis of the criteria for the plasticity of Huber - Mises and Tresca - Saint-Venant, the radius at which the first plastic deformations occur is determined. It is shown that, depending on the functions of the inhomogeneity of elastic and plastic parameters and loads, the occurrence of plastic deformations is possible both on the surfaces and on the inner walls of the cylinder.

Abstract: The article deals with the axisymmetric elastoplastic problem for a hollow thick-walled ball (plane deformed state), loaded from the inside and outside by uniform pressures proportional to one parameter. The material is considered to be perfectly plastic, with the elastic modulus and yield strength generally are arbitrary functions of the radius. In addition, the material is considered to be incompressible in both plastic and elastic zones. On the basis of the criteria for the plasticity of Huber - Mises and Tresca - Saint-Venant, the radius at which the first plastic deformations occur is determined. It is shown that, depending on the functions of the inhomogeneity of elastic and plastic parameters and loads, the occurrence of plastic deformations is possible both on the surfaces and on the inner walls of the ball.

Abstract: Two-phase materials, such as α+β Titanium (Ti) alloys, are technologically important. A number of factors can affect deformation behavior, including the interaction stresses between phases, the crystallographic relationships between phases, and the morphology. As a result, the deformation mechanisms of two-phase alloys may be different from the individual single-phase materials. For example, twinning may not occur in a single phase material if the grain size is very small but twinning can occur in a very fine grained alloy if the second phase contributes to the interfacial stresses due to elastic interactions. Interaction stresses can result from the difference in the elastic properties of the two phases. In particular, these elastic interaction stresses can be quantified by the finite element method (FEM). In this paper recent developments regarding two-phase deformation mechanisms will be reviewed and the ramifications on mechanical behavior in regard to two-phase Ti alloys in particular and on two-phase metallic materials in general will be outlined.

Abstract: In the constructions of multilayer cylindrical shells in heat-and-power engineering the materials, exhibiting rheological properties, such as concrete, polymers or fiber glass are widely used. In this connection, the study of temperature stresses in polymers, the analysis of the influence of various factors on the processes course under consideration, is of great importance. The paper presents an analytical solution of the thermal creep problem in polymers using the Kelvin-Voigt model for a rigidly clamped rod for various cases of temperature loading. The analysis of these solutions is also made on the example of a specific material for certain laws with changing temperature loads.

Abstract: The paper deals with the analysis of the effect of the thermal mechanical processing on the mechanical characteristics (elasticity and tensile strength) of the welded joints of the aluminum alloy, the system Al-Mg-Li. The microstructures of the basic alloy and welded joint before and after the thermal processing are compared by electronic microscoping. The X-ray diffraction method is used to compare the phase composition. The concentration of the strengthening phase δʹ(Al₃Li) reduces in the welded joint, which results in the low mechanical characteristics. The thermal processing, namely quenching, increases the concentration of the equilibrium S₁ phase (Al₂MgLi) in the welded joint as compared with an unquenched joint. The elasticity of the welded joint rises significantly at the almost constant strength, the value of the relative extension lies within the range of 2.4 – 19.2 % before and after quenching, respectively. Artificial ageing applied to the welded joint after the quenching gives the structurization of the S1 phase. The full thermal mechanical processing (quenching, elastic deformation, artificial ageing) of the welded joint of the aluminum alloy (the system AL-Mg-Li) results in the tensile strength increase up to 0.95 of the basic alloy strength.

Abstract: The non-local Timoshenko beam theory has been implemented to investigate the free vibration of armchair single-walled carbon nanotubes embedded in elastic medium including the thermal effects. The mechanical properties of nano-composite (carbon nanotubes and polymer matrix) are treated as functions of temperature change and the analytical solution is derived according to the governing equations of non-local Timoshenko beam models. The equivalent Young’s modulus and shear modulus for armchair single-walled carbon nanotubes are derived using an energy-equivalent model. Influence of small-scale coefficient, vibrational mode number, matrix of nano-composite and aspect ratio on the frequency ratio of the armchair single-walled carbon nanotubes including the thermal effect are studied and discussed. The research work reveals the significance of the small-scale coefficient, the vibrational mode number, the elastic medium and the aspect ratio on the frequency ratio. It is also demonstrated that some properties of free vibrations of single-walled carbon nanotubes are dependent on the change of temperature.

Abstract: Microcapsules are used in a wide range of applications, especially in self-healing composite materials and phase change materials. There is a growing body of literature that recognizes the importance of reinforcement on the mechanical properties of composites, however the effect of microcapsules during service needs to be further investigated. In this study, numerical investigations were conducted to examine the effects of the various geometric parameters on the mechanical behavior of microcapsules-based composites. The effective Young’s modulus and Poisson’s ratio of core-shell microcapsules distributed in a continuous matrix were predicted. A detailed three-dimensional finite element modeling (FEM) was presented. The numerical results were compared with a hierarchical proposed analytical model for three-constituent composites. Good agreements were achieved.

Abstract: The structure of the thin liquid films determines the stability of foams and emulsions. In this work the bubbles stretched length with different hollow SiO₂ particles concentration is measured when the foam has been stilled for different time. The results show that the bubbles stretched length is longer than that of bubbles when the foam is free of hollow SiO₂ particles even when the foam has been stilled for 500mins. The bubbles stretched length increases with increasing the concentration of hollow SiO₂ particles. A strong hydration effect leaves a large volume of hydration layers on the solid particles surfaces in aqueous solutions. The water in hydration layers can help the film keep a certain thickness. The existence of hydration forces leads that two particles cannot be too close each other. The high concentration surfactant limited in the fixed area helps the film keep good elasticity. Therefore the film has a long life time with compatible thickness and elasticity and the three-phrase foam is upper stable.