Abstract in English:Abstract This study has been undertaken to investigate the mechanical behavior of the capacitive microphone with clamped circular diaphragm using modified couple stress theory in comparison to the classical one. Presence of the length scale parameter in modified couple stress theory provides the means to evaluate the size effect on the microphone mechanical behavior. Investigating Pull-in phenomenon and dynamic behavior of the microphone are the matters provided due to the application of a step DC voltage. Also the effects of different air damping coefficients on dynamic pull-in voltage and pull-in time have been studied. The output level or sensitivity of the microphone has been studied by investigating the frequency response in term of magnitude for different length scale parameters to figure out how the length scale parameter affects on the sensitivity of the capacitive microphone. To achieve these ends, the nonlinear differential equation of the circular diaphragm has been extracted using Kirchhoff thin plate theory. Then, a Step-by-Step Linearization Method (SSLM) has been used to escape from the nonlinearity of the differential equation. Afterwards, Galerkin-based reduced-order model has been applied to solve the obtained equation.
Abstract in English:Abstract The differential quadrature method (DQM) has been so far applied to a wide variety of fluid and/or structural problems. The results of many researchers reveal that the DQM is computationally efficient and is applicable to a large class of boundary value problems. However, there is little information about its applications to fluid-structure interaction problems. Therefore, the purpose of this paper is to provide some information in this area and to develop procedures based on the DQM for the numerical solution of fluid-structure interaction problems. First, the governing partial differential equations of motion of the structure and fluid are discretized separately using the DQM. Then, by applying the boundary condition at fluid-structure interface, the governing eigenvalue equations of the coupled system are obtained which can then be solved for the eigenvalues of the system. The applicability of the proposed procedures is shown herein through the free vibration analysis of thin circular plates in contact with a cylindrical fluid-filled cavity. Issues related to the implementation of the regularity conditions at the center of the circular plate and the central line of the cylindrical cavity are addressed. Two new regularity conditions are proposed for the circular cylindrical fluid domain. The accuracy and efficiency of the proposed procedures are demonstrated by comparing the obtained results with those available in the literature. It is shown that highly accurate converged results can be obtained by the proposed procedures using a small number of grid points. Three new dimensionless parameters and variables are also introduced for the free vibration of the coupled system. The influences of these parameters on dynamic behavior of the system are studied.
Abstract in English:Abstract In this paper, a size-dependent microscale plate model is developed to describe the bending, buckling and free vibration behaviors of microplates made of functionally graded materials (FGMs). The size effects are captured based on the modified strain gradient theory (MSGT), and the formulation of the paper is on the basis of Mindlin plate theory. The presented model accommodates the models based upon the classical theory (CT) and the modified couple stress theory (MCST) if all or two scale parameters are set to zero, respectively. By using Hamilton's principle, the governing equations and related boundary conditions are derived. The bending, buckling and free vibration problems are considered and are solved through the generalized differential quadrature (GDQ) method. A detailed parametric and comparative study is conducted to evaluate the effects of length scale parameter, material gradient index and aspect ratio predicted by the CT, MCST and MSGT on the deflection, critical buckling load and first natural frequency of the microplate. The numerical results indicate that the model developed herein is significantly size-dependent when the thickness of the microplate is on the order of the material scale parameters.
Abstract in English:Abstract A series of dynamic tests were conducted on a closed-cell aluminum alloy foams in order to determine experimental failure surface under impact loading conditions. Quasi-static tests have also been performed to investigate failure mechanism under different stress paths. Three typical types of deformation modes can be observed, which corresponds to the different failure mechanism. The failure loci of the foam in principal stress plane are explored from quasi-static to dynamic loading conditions. A signiﬁcant strength enhancement is identified experimentally. The expansion of the failure locus from the quasi-static to the dynamic test is almost isotropic. A modified failure criterion for the metallic foam is proposed to predict failure locus as a function of strain rate. This rate-dependence failure criterion is capable of giving a good description of the biaxial failure stresses over a wide range of the strain rates.
Abstract in English:Abstract A 1D Finite Element model for static response and free vibration analysis of functionally graded material (FGM) beam is presented in this work. The FE model is based on efficient zig-zag theory (ZIGT) with two noded beam element having four degrees of freedom at each node. Linear interpolation is used for the axial displacement and cubic hermite interpolation is used for the deflection. Out of a large variety of FGM systems available, Al/SiC and Ni/Al2O3 metal/ceramic FGM system has been chosen. Modified rule of mixture (MROM) is used to calculate the young's modulus and rule of mixture (ROM) is used to calculate density and poisson's ratio of FGM beam at any point. The MATLAB code based on 1D FE zigzag theory for FGM elastic beams is developed. A 2D FE model for the same elastic FGM beam has been developed using ABAQUS software. An 8-node biquadratic plane stress quadrilateral type element is used for modeling in ABAQUS. Three different end conditions namely simply-supported, cantilever and clamped- clamped are considered. The deflection, normal stress and shear stress has been reported for various models used. Eigen Value problem using subspace iteration method is solved to obtain un-damped natural frequencies and the corresponding mode shapes. The results predicted by the 1D FE model have been compared with the 2D FE results and the results present in open literature. This proves the correctness of the model. Finally, mode shapes have also been plotted for various FGM systems.
Abstract in English:Abstract In this work we consider a problem in the context of the generalized theory of thermoelasticity for a half space. The material of the half space is functionally graded in which Lamé's modulii are functions of the vertical distance from the surface of the medium. The surface is traction free and subjected to a time dependent thermal shock. The problem was solved by using the Laplace transform method together with the perturbation technique. The obtained results are discussed and compared with the solution when Lamé's modulii are constants. Numerical results are computed and represented graphically for the temperature, displacement and stress distributions.
Abstract in English:Abstract In conventional composite construction involving hot-rolled steel section, the composite action is usually achieved by using conventional headed shear studs connectors. However, use of headed studs is not practical for cold-formed steel (CFS) section due to its very thin form that is difficult to weld. A suitable bolt and nut type shear connector was proposed; experimental tests were carried out to evaluate its performance. This study also investigated the use of Self-Compacting Concrete (SCC) integrated with CFS by means of bolted shear connectors to develop composite action. Therefore, the objective of this paper was to investigate the performance of bolted shear connectors in SCC integrated with CFS section as composite beam system. Eighteen push-out test specimens comprising of M12, M14 and M16 sized bolted shear connector of grade 8.8 with longitudinal spacings of 150 mm, 250 mm and 300 mm centers were fabricated, cast and tested until failure. The experimental results showed that all bolted shear connectors possessed a good shear resistance capacity. Not much difference in strength capacity of specimens with M14 and M16 bolted shear connectors was found, perhaps due to CFS failure. Varying the size and longitudinal spacing of the bolted shear connectors revealed that the connectors' strength capacity changed slightly between M14 and M16 bolts specimens but, significantly for M12 bolt specimens.
Abstract in English:Abstract Using the third-order shear deformation theory (TSDT), an analytical solution for deformations and stresses of axisymmetric clamped-clamped thick cylindrical shells made of functionally graded material (FGM) subjected to internal pressure and thermal loading are presented. The material properties are graded along the radial direction according to power functions of the radial direction. It is assumed that Poisson's ratio is constant across the cylinder thickness. The differential equations governing were generally derived, making use of TSDT. Following that, the set of non-homogenous linear differential equations for the cylinder with clamped-clamped ends was solved, and the effect of loading and supports on the stresses and displacements was investigated. The problem was also solved, using the finite element method (FEM), and the results of which were compared with those of the analytical method. Furthermore, the effect of increases in the temperature gradient on displacement and stress values has been studied. Finally, in order to investigate the effect of third-order approximations on displacements and stresses, a comparison between the results of first- and third-order shear deformation theory has been made.
Abstract in English:Abstract The paper concerns topology and geometry optimization of statically determinate beams with an arbitrary number of pin supports. The beams are simultaneously exposed to uniform dead load and arbitrarily distributed live load and optimized for the absolute maximum bending moment. First, all the beams with fixed topology are subjected to geometrical optimization by genetic algorithm. Strict mathematical formulas for calculation of optimal geometrical parameters are found for all topologies and any ratio of dead to live load. Then beams with the same minimal values of the objective function and different topologies are classified into groups called topological classes. The detailed characteristics of these classes are described.
Abstract in English:Abstract In the present paper, the aerothermoelastic behavior of Functionally Graded (FG) plates under supersonic airflow is investigated using Generalized Differential Quadrature Method (GDQM). The structural model is considered based on the classical plate theory and the von Karman strain-displacement relations are utilized to involve the nonlinear behavior of the plate. To consider the supersonic aerodynamic loads on the plate, the first order piston theory is applied. The material properties of the FG panel are assumed to be temperature independent and alter in the thickness direction according to a power law distribution. The temperature distribution on the surface of the plate is assumed to be constant and in the thickness direction is obtained by one-dimensional steady conductive heat transfer equation. The discretized governing equations via GDQM are solved by the fourth order Runge-Kutta method. Comparison of the obtained results with those available in literature confirms the accuracy and ability of the GDQM to perform the aerothermoelastic analysis of FG plates. Also, the effect of some important parameters such as Mach number, in-plane thermal load, plate aspect ratio and volume fraction index on the plate aerothermoelastic behavior is examined.