• Structural Engineering and Mechanics
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• v.85 no.1
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• pp.1-14
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• 2023

The use of functionally graded materials in applications involving severe thermal gradients is quickly gaining acceptance in the composite mechanics community, the aerospace and aircraft industry. In the present study, a refined sandwich plate model is applied to study the free vibration analysis of porous functionally graded material (FGM) sandwich plates with various distribution rate of porosity. Two types of common FG sandwich plates are considered. The first sandwich plate is composed of two FG material (FGM) face sheets and a homogeneous ceramic or metal core. The second one consists of two homogeneous fully metal and ceramic face sheets at the top and bottom, respectively, and a FGM core. The displacement field of the present theory is chosen based on nonlinear variations in the in-plane displacements through the thickness of the sandwich plate. The number of unknowns and equations of motion of the present theory is reduced and hence makes them simple to use. In the analysis, the equation of motion for simply supported sandwich plates is obtained using Hamilton's principle. In order to present the effect of the variation of the porosity distribution on the dynamic behavior of the FGM sandwich plates, new mixtures are proposed which take into account different rate of porosity distribution between the ceramic and the metal. The present method is applicable to study the dynamic behavior of FGM plates and sandwich plates. The frequencies of two kinds of FGM sandwich structures are analyzed and discussed. Several numerical results have been compared with the ones available in the literature.

• Journal of the Korean Wood Science and Technology
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• v.50 no.4
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• pp.219-236
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• 2022

Wood-based nanocomposite electrode materials were synthesized for application in supercapacitors by mixing nanostructured hematite (Fe₂O₃) with highly porous activated carbon (AC) produced from the wood-waste of Pinus roxburghii. The AC was characterized using various instrumental techniques and the results showed admirable electrochemical properties, such as high surface area and reasonable porosity. Firstly, AC was tested as an electrode material for supercapacitors and it showed a specific capacitance of 59.02 Fg^-1 at a current density of 1 Ag^-1, cycle life of 84.2% after 1,000 cycles (at a current density of 3 Ag^-1), and energy density of 5.1 Wh/kg at a power density of 135 Wkg^-1. However, when the AC was composited with different ratios of Fe₂O₃ (1:1, 2:1, and 1:2), there was an overall improvement in its electrochemical performance. Among the 3 ratios, 2:1 (AC:Fe₂O₃) had the best specific capacitance of 102.42 Fg^-1 at 1 Ag^-1, cycle life of 94.4% capacitance after 1,000 cycles (at a current density of 3 Ag^-1), and energy density of 8.34 Wh/kg at a power density of 395.15 Wkg^-1 in 6 M KOH electrolyte in a 3-electrode experimental setup with a high working voltage of 1.55 V. Furthermore, when Fe₂O₃ was doubled, 1:2 (AC:Fe₂O₃), the electrochemical capacitive performance of the electrode twisted and deteriorated due to either the accumulation of Fe₂O₃ particles within the composite or higher bulk resistance value of pure Fe₂O₃.

• Advances in nano research
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• v.12 no.1
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• pp.101-115
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• 2022

Some researchers pointed out that the nonlocal cantilever models do not predict the dynamic softening behavior for nanostructures (including nanobeams) with clamped-free (CF) ends. In contrast, some indicate that the nonlocal cantilever models can capture the stiffness softening characteristics. There are substantial differences on this issue between them. The vibration analysis of porosity-dependent functionally graded nanoscale tubes with variable boundary conditions is investigated in this study. Using a modified power-law model, the tube's porosity-dependent material coefficients are graded in the radial direction. The theory of nonlocal strain gradients is used. Hamilton's principle is used to derive the size-dependent governing equations for simply-supported (S), clamped (C) and clamped-simply supported (CS). Following the solution of these equations by the extended differential quadrature technique, the effect of various factors on vibration issues was investigated further. It can be shown that these factors have a considerable effect on the vibration characteristics. It also can be found that our numerical results can capture the unexpected softening phenomena for cantilever tubes.

• Structural Engineering and Mechanics
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• v.85 no.3
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• pp.289-304
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• 2023

The main objective of this paper is to study the effect of porosity on the buckling behavior of thick functionally graded sandwich plate resting on various boundary conditions under different in-plane loads. The formulation is made for a newly developed sandwich plate using a functional gradient material based on a modified power law function of symmetric and asymmetric configuration. Four different porosity distribution are considered and varied in accordance with material propriety variation in the thickness direction of the face sheets of sandwich plate, metal foam also is considered in this study on the second model of sandwich which containing metal foam core and FGM face sheets. New quasi-3D high shear deformation theory is used here for this investigate; the present kinematic model introduces only six variables with stretching effect by adopting a new indeterminate integral variable in the displacement field. The stability equations are obtained by Hamilton's principle then solved by generalized solution. The effect of Pasternak and Winkler elastic foundations also including here. the present model validated with those found in the open literature, then the impact of different parameters: porosities index, foam cells distribution, boundary conditions, elastic foundation, power law index, ratio aspect, side-to-thickness ratio and different in-plane axial loads on the variation of the buckling behavior are demonstrated.

• Steel and Composite Structures
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• v.46 no.4
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• pp.471-483
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• 2023

This paper presents an analytical hyperbolic theory based on the refined shear deformation theory for mechanical stability analysis of the simply supported advanced composites plates (exponentially, sigmoidal and power-law graded) under triangular, trapezoidal and uniform uniaxial and biaxial loading. The developed model ensures the boundary condition of the zero transverse stresses at the top and bottom surfaces without using the correction factor as first order shear deformation theory. The mathematical formulation of displacement contains only four unknowns in which the transverse deflection is divided to shear and bending components. The current study includes the effect of the geometric imperfection of the material. The modeling of the micro-void presence in the structure is based on the both true and apparent density formulas in which the porosity will be dense in the mid-plane and zero in the upper and lower surfaces (free surface) according to a logarithmic function. The analytical solutions of the uniaxial and biaxial critical buckling load are determined by solving the differential equilibrium equations of the system with the help of the Navier's method. The correctness and the effectiveness of the proposed HyRPT is confirmed by comparing the results with those found in the open literature which shows the high performance of this model to predict the stability characteristics of the FG structures employed in various fields. Several parametric analyses are performed to extract the most influenced parameters on the mechanical stability of this type of advanced composites plates.