2D magneto-mechanical vibration analysis of a micro composite Timoshenko beam resting on orthotropic medium

Mojtaba Mehrabi,Mehdi Mohammadimehr,Fatemeh S. Mousavinejad 국제구조공학회 2021 Smart Structures and Systems, An International Jou Vol.27 No.1

In the present study, the free vibration analysis of a size-dependent micro composite Timoshenko beam model reinforced by various distributions of carbon nanotubes under temperature changes and two-dimensional magnetic field is investigated based on modified strain gradient theory. Also, the effects of environment are simulated by orthotropic elastic foundation and it is assumed that the material properties are temperature-dependent. Mathematical formulations are obtained using Hamilton's principle and the governing equations of motion are derived based on energy approach and variation method. These equations are solved using semi-analytical and numerical methods such as Navier's type solution, finite element method and generalized differential quadrature method for various boundary conditions. The obtained results of this study are compared with the other previous researches and there is a good agreement between them. The main purpose of this work is the comparison of various solution methods on the problem outputs. Thus, the results are compared together and the effects of solution approach on the dimensionless natural frequencies is developed. Moreover, the effects of length-to-thickness ratio, magnetic field, temperature changes, elastic foundation and carbon nanotubes volume fractions on the dimensionless natural frequencies are studied. The results of this article demonstrate that the micro composite Timoshenko beam reinforced by FG-O and FG-X CNTs have lowest and highest dimensionless natural frequency, respectively. It is investigated that the dimensionless natural frequency enhances by increasing the magnetic field in x and z-directions.

Surface and size dependent effects on static, buckling, and vibration of micro composite beam under thermo-magnetic fields based on strain gradient theory

Mehdi Mohammadimehr,Mojtaba Mehrabi,Hasan Hadizadeh,Hossein Hadizadeh 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.26 No.4

In this article, static, buckling and free vibration analyses of a sinusoidal micro composite beam reinforced by single-walled carbon nanotubes (SWCNTs) with considering temperature-dependent material properties embedded in an elastic medium in the presence of magnetic field under transverse uniform load are presented. This system is used at micro or sub micro scales to enhance the stiffness of micro composite structures such as bar, beam, plate and shell. In the present work, the size dependent effects based on surface stress effect and modified strain gradient theory (MSGT) are considered. The generalized rule of mixture is employed to predict temperature-dependent mechanical and thermal properties of micro composite beam. Then, the governing equations of motions are derived using Hamilton's principle and energy method. Numerical results are presented to investigate the influences of material length scale parameters, elastic foundation, composite fiber angle, magnetic intensity, temperature changes and carbon nanotubes volume fraction on the bending, buckling and free vibration behaviors of micro composite beam. There is a good agreement between the obtained results by this research and the literature results. The obtained results of this study demonstrate that the magnetic intensity, temperature changes, and two parameters elastic foundations have important effects on micro composite stiffness, while the magnetic field has greater effects on the bending, buckling and free vibration responses of micro composite beams. Moreover, it is shown that the effects of surface layers are important, and observed that the changes of carbon nanotubes volume fraction, beam length-to-thickness ratio and material length scale parameter have noticeable effects on the maximum deflection, critical buckling load and natural frequencies of micro composite beams.

Temperature distribution of ceramic panels of a V94.2 gas turbine combustor under realistic operation conditions

Namayandeh, Mohammad Javad,Mohammadimehr, Mehdi,Mehrabi, Mojtaba Techno-Press 2019 Advances in materials research Vol.8 No.2

The lifetime of a gas turbine combustor is typically limited by the durability of its liner, the structure that encloses the high-temperature combustion products. The primary objective of the combustor thermal design process is to ensure that the liner temperatures do not exceed a maximum value set by material limits. Liner temperatures exceeding these limits hasten the onset of cracking which increase the frequency of unscheduled engine removals and cause the maintenance and repair costs of the engine to increase. Hot gas temperature prediction can be considered a preliminary step for combustor liner temperature prediction which can make a suitable view of combustion chamber conditions. In this study, the temperature distribution of ceramic panels for a V94.2 gas turbine combustor subjected to realistic operation conditions is presented using three-dimensional finite difference method. A simplified model of alumina ceramic is used to obtain the temperature distribution. The external thermal loads consist of convection and radiation heat transfers are considered that these loads are applied to flat segmented panel on hot side and forced convection cooling on the other side. First the temperatures of hot and cold sides of ceramic are calculated. Then, the thermal boundary conditions of all other ceramic sides are estimated by the field observations. Finally, the temperature distributions of ceramic panels for a V94.2 gas turbine combustor are computed by MATLAB software. The results show that the gas emissivity for diffusion mode is more than premix therefore the radiation heat flux and temperature will be more. The results of this work are validated by ANSYS and ABAQUS softwares. It is showed that there is a good agreement between all results.

Temperature and thermal stress distributions in a hollow circular cylinder composed of anisotropic and isotropic materials

Namayandeh, Mohammad Javad,Mohammadimehr, Mehdi,Mehrabi, Mojtaba,Sadeghzadeh-Attar, Abbas Techno-Press 2020 Advances in materials research Vol.9 No.1

In this article, an analytical solution is presented for the steady-state axisymmetric thermal stress distributions in a composite hollow cylinder. The cylinder is composed of two isotropic and anisotropic materials which is subjected to the thermal boundary conditions of convective as well as radiative heating and cooling on the inner and outer surfaces, respectively. The solution of the temperature is obtained by means of Bessel functions and the thermal stresses are developed using Potential functions of displacement. Numerical results are derived for a cylinder which is similar to a gas turbine combustor and showed that the maximum temperature and thermal stresses (radial, hoop, axial) occurred in the middle point of cylinder and the values of thermal stresses in anisotropic cylinder are more than the isotropic cylinder. It is worthy to note that the values of the thermal conditions which estimated in this research, not to be presented in any other papers but these values are very accurate in calculation.

Free vibration and buckling of functionally graded carbon nanotubes / graphene platelets Timoshenko sandwich beam resting on variable elastic foundation

Nejadi, Mohammad Mehdi,Mohammadimehr, Mehdi,Mehrabi, Mojtaba Techno-Press 2021 Advances in nano research Vol.10 No.6

Sandwich structures made of composites are widely applicable in different industries, including aerospace and power plants. The combination of a porous sandwich with functionally graded materials makes structures more resistant to analyze buckling and vibration behaviors. According to its high surface area and high strength, adding graphene platelets to the composite increases the final mechanical properties of composites. In the present paper, the effect of volume fraction distribution of fibers, numbers, and angles of layers in composites will be investigated. Additionally, the different porosity coefficients and distribution along the beam length will consider and the best porosity distributions will identify. Pasternak elastic foundation is considered during the beam length as linearly and parabolically. The equations of motion for the Timoshenko sandwich beam are solved by the differential quadrature method (DQM). The influences of adding graphene platelets with three various patterns on critical buckling load and natural frequency of composite beam will investigate. Also, the buckling and vibration behaviors of pure composites, perfect composite and FGM (Functionally Graded Material) composites will compare. Moreover, the critical buckling load will obtain by the Mori-Tanaka model.

Free vibration and buckling analyses of functionally graded annular thin sector plate in-plane loads using GDQM

Mehdi Mohammadimehr,Hasan Afshari,M. Salemi,K. Torabi,Mojtaba Mehrabi 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.71 No.5

In the present study, buckling and free vibration analyses of annular thin sector plate made of functionally graded materials (FGMs) resting on visco-elastic Pasternak foundation, subjected to external radial, circumferential and shear in-plane loads is investigated. Material properties are assumed to vary along the thickness according to an power law with Poisson’s ratio held constant. First, based on the classical plate theory (CPT), the governing equation of motion is derived using Hamilton’s principle and then is solved using the generalized differential quadrature method (GDQM). Numerical results are compared to those available in the literature to validate the convergence and accuracy of the present approach. Finally, the effects of power-law exponent, ratio of radii, thickness of the plate, sector angle, and coefficients of foundation on the fundamental and higher natural frequencies of transverse vibration and critical buckling loads are considered for various boundary conditions. Also, vibration and buckling mode shapes of functionally graded (FG) sector plate have been shown in this research. One of the important obtained results from this work show that ratio of the frequency of FG annular sector plate to the corresponding values of homogeneous plate are independent from boundary conditions and frequency number.