This work is dedicated to the modeling and solution of eigenvalue problems within shear deformation theory (SDT) of laminated cylindrical shells containing nanocomposite plies subjected to axial compressive load in thermal environments. In this study, the shear deformation theory for homogeneous laminated shells is extended to laminated shells consisting of functionally graded (FG) nanocomposite layers. The nanocomposite plies of laminated cylindrical shells (LCSs) are arranged in a piecewise FG distribution along the thickness direction. Temperature-dependent material properties of FG-nanocomposite plies are estimated through a micromechanical model, and CNT efficiency parameters are calibrated based on polymer material properties obtained from molecular dynamics simulations. After mathematical modeling, second-order time-dependent and fourth-order coordinate-dependent partial differential equations are derived within SDT, and a closed-form solution for the dimensionless frequency parameter and critical axial load is obtained for first time. After the accuracy of the applied methodology is confirmed by numerical comparisons, the unique influences of ply models, the number and sequence of plies and the temperature on the critical axial load and vibration frequency parameter within SDT and Kirchhoff–Love theory (KLT) are presented with numerical examples. © The Author(s) 2024.
Nowadays, beams, boards and coatings with new complex properties are widely used in many branches of mechanical engineering and construction. The calculation and analysis of the amplitude characteristics of stability, strength and frequency of a structural element with these properties lead both to significant difficulties in mathematical terms and to the analysis of the results obtained, if ignored, serious errors may be made. Taking these into account, it becomes necessary to build mathematical models characterizing the real properties of the material when using a structural element made of new materials and establishing effective physical connections. There are materials in which the tensile strain diagrams characterizing their properties are diverse in tension-compression and torsion. Such materials include ceramics, some types of copper and cast iron, polymers, and composite materials. The mechanical and physical properties of these materials become strictly dependent on hydrostatic pressure. For materials with the above-mentioned specific property, classical elasticity and elastoplasticity cannot be considered under the conditions accepted by the theory of plasticity. In this paper, a problem of planar stability of an elastic, plastic plane differently resisting to tension and compression in pure bending is solved. It is assumed that the cross-section of the beam has one symmetry axis, under the action of concentrated moments applied at the ends of the bar is subjected to pure bending, and bending happens in the symmetry plane of the beam. Using the state of a neutral axis, absence of longitudinal force, continuity conditions for tension and compression, we determine the boundary of elastic and plastic domains. The equations of the loss of planar stability obtained for the classic case are reduced to the loss of planar stability for various modulus ideal elastic and plastic beams. The expressions of hardness for different modulus materials are obtained and are associated with critical moment and critical length. Expressions for calculating critical parameters for an ideally elastic, plastic beam with a rectangular cross section are obtained. © 2024, International Organization on 'Technical and Physical Problems of Engineering'. All rights reserved.
Increasing the properties of iron-based abrasive composition materials by volume and surface alloying is of scientific and technical importance. Since increasing the properties of composite materials by volume alloying causes a number of difficulties, surface alloying is often used to improve the properties of this type of materials. Therefore, in order to increase the properties, successive saturation processes of their surface layer with one or more carbide-forming elements are carried out. It was found that the properties enhancement with one-component coatings differs from the properties of multi-component coatings. It is clear that as a result of the saturation of the surface layer of the abrasive composition materials with certain elements, coatings with different composition are created in them. Carbide, nitride, boride and other coatings allow to obtain the necessary results. Therefore, the improvement of the structure and properties of iron-based abrasive composition materials directly depends on the coatings formed as a result of hammering the surface layer of construction materials with various elements. In the article, the effect of carbide, nitride and boride-containing coatings on the structure and properties of iron-based abrasive composition materials was considered. The distribution of chromium in the depth of the diffusion layer was studied by the method of micro-X-ray spectral analysis. The greatest concentration of chromium is observed on the surface, which increases as the degree of carbonization of the material increases. The change of the amount of chromium on the depth of the carbide zone obeys a linear law. At the boundary of the carbide zone, its concentration is approximately the same in the studied materials and is 58-61% In connection with the increase in the initial carbonization degree of the surface zone, the increase in the concentration of chromium is accompanied by the increase in the microhardness of the carbide coating. Based on the data of X-ray structural studies, the studied carbide coatings have the same phase composition (Cr, Fe) C 23 6, (Cr,Fe) C 7 3. The structure of the transition zone and its layers is determined by the degree of carbonization of the material during the initial processing. At relatively low temperatures (875 and 925 °C) in cementitized iron, as in the case of JQr 0.5 composition, a weakly tanned zone (20-25 μm thick) of an extremely saturated γ-solid solution with a microhardness H100 = 6100-7000 MPa, formed in the process of cooling from the air chroming temperature directly under the carbide layer is located. Behind it is a zone of high etching ability, which is caused by the eutectoid decomposition of the solid solution of chromium and carbon in γ-iron. The intermediate zone of annealed iron cementitized at 975-1025 °C undergoes eutectoid decomposition during cooling in air and metallographically is detected as a band with high etching ability. © 2024, International Organization on 'Technical and Physical Problems of Engineering'. All rights reserved.
The article presents a theoretical and experimental assessment of noise levels during the analog-to-digital conversion of TV broadcast microwave signals. Mathematical expressions are derived to calculate the mean quantization noise power for different brightness distribution models on TV images, considering both linear and nonlinear characteristics of the “light-to-signal” converter. For the first time, the dependence of the average quantization noise power on the compression coefficient is obtained for an inversely proportional distribution of brightness on the television image. This is particularly relevant when the input unipolar positive TV broadcast luminance signal is small, i.e., when the signal level is below the first quantization level. Additionally, analytical expressions are provided to calculate the level of restriction noise and the ratio of restriction noise power to quantizing noise power, particularly when the brightness distribution on TV images follows an exponentially decreasing model or an inversely proportional model with a logarithmic quantization scale. The impact of quantization and restriction noise on image quality was experimentally tested in an Additive White Gaussian Noise (AWGN) channel. © (2024), (International Academy of Microwave and Optical Technology (IAMOT)). All rights reserved.
Underground sewer reinforced concrete pipes of large diameter are subject to accidents and deform. Therefore, fiber-reinforced concrete pipes and their stress-strain state under the action of seismic load and soil settlement are investigated in the work. The structure is modeled in PLAXIS 2D and 3D software. These programs are based on the finite element method. In plane and spatial problems, respectively, triangular and tetrahedral finite elements were used. In each finite element, 15 nodes (for a triangular element) and 10 nodes (for a tetrahedral element) were used. The values of stresses and strains in the pipe are determined from the action of a seismic load acting perpendicular to the longitudinal axis of the pipe and soil settlement under the pipe. The study of the strength and crack resistance of underground pipelines showed that with an increase in the diameter of the pipes, the influence of the horizontal component of the seismic load is the cause of the failure of the pipes. Therefore, the manufacture of pipes from fiber-reinforced concrete and the strengthening of the soil base under the pipeline is an important engineering task. The mechanical characteristics of the fiber-reinforced concrete material, such as the modulus of elasticity, Poisson's ratio, tensile resistance, were determined in the laboratory, and then taken into account in the calculation program. © 2024, International Organization on 'Technical and Physical Problems of Engineering'. All rights reserved.