جستجوی مقالات مرتبط با کلیدواژه « functionally graded materials » در نشریات گروه « مکانیک »

Nowadays, rotating cylindrical shells have industrial applications such as centrifuges, turbines, dryers, rotating shafts, motors and rotors. Therefore, it seems necessary to study their vibrations. This research analyzes and investigates the effect of elastic mechanical properties on shell-like and beam-like behavior in the vibrations of cylindrical shells made of materials with gradient properties (FGM) with different boundary conditions, considering the effect of the length scale parameter with values different and also the effect of varying radius and thickness has been discussed. The results show that the modulus of elasticity and Poisson's ratio with different values ​​have no effect on the vibration behavior of cylindrical shells made of materials with gradient properties, and also with the increase of the constraint (boundary conditions), the displacement (displacement) is less and the natural frequency increases. and the effect of the boundary conditions decreases with the increase of the length parameter. Finally, a relationship has been obtained to show the behavior change from shell-like to arrow-like. The results are in good agreement with other literature.

In this study, it is assumed that the outer shell of the sandwich has a core made of functional calibrated materials with piezoelectric patches and the inner shell is made of layered composites. Double-walled cylindrical shells have three external, internal and middle acoustic environments and are exposed to acoustic waves with a specific angle of effect. The dynamic equations of the structure are derived using the hypothesis of first-order shear displacement field of shells and Hamilton principle and together with the fluid / structure boundary conditions form the final equations. Using the Fourier series expansions of the input, return, and output sound pressures and shell displacements, the dynamic equations are discretized to form a state matrix. After validating the results with existing articles, finally the effects, voltage applied by piezoelectric patches, percentage of functional materials, angle of fibers used in composites, types of composite materials, number of piezoelectric patches and angle of impact on the structure of sound transmission behavior It has been evaluated in a certain frequency range. Finally, the voltage parameters applied by the piezoelectric patches, the percentage of functional materials, the angle of the fibers used in the composites, the types of composite materials, the number of piezoelectric patches and the angle of impact increased the sound loss.

In this study, sound transmission loss of a cylindrical shell made out of functionally graded materials with an arrangement of piezoelectric patches is investigated in the framework of the first-order shear deformation theory. Also, power law model is utilized to take into account material characteristics distribution along the thickness of the shell. It is noteworthy that both outer and inner piezoelectric patches are used as actuator and sensor. The structure is immersed in an acoustic medium of air and is subjected to acoustic waves with certain incident angle. The derivation of vibroacoustic equations in the form of coupled relations is realized by implementing Hamilton’s principle in conjunction with fluid/structure compatibility conditions. An analytical method is exploited to solve the coupled vibroacoustic governing equations with Fourier series. After validation study, parameter studies reveal the effects of the functionally graded index, incident angles, external electric voltage, and characteristics of piezoelectric patches on the sound transmission loss behavior of the structure in a certain frequency domain. Results indicated that with increasing the power law index, sound transmission loss decreases in the low-frequency region. Also, the applied voltage is able to improve the sound transmission loss especially in high-frequency region.

The free vibration features of rotating functionally graded microbeams in thermal environmentare presented in this paper. The governing equations are extracted on the basis of the Euler-Bernoulli beam assumptions beside the modified couple stress theory. The finite elementmethod is applied on the weak form of the strain and the kinetic energies to extract the naturalfrequencies and the associated modeshapes. The nonlinear static equations of motion due to therotation and the thermal environment are treated employing the Newton-Raphson technique.Moreover, the natural frequencies are estimated from the linearized equations of motion aboutthe static configuration. After the validation of the present results, the rotation speed, thematerial length scale parameter, the temperature change, the power law exponent and theslenderness ratio impacts on the fundamental natural frequency and the first and the secondmodeshapes are examined. The outcomes indicate the increment of the natural frequency aftera threshold value of the power law exponent depends on a given rotation speed for the rotatingmicrobeams in comparison with the stationary microbeams. Furthermore, the modeshapes ofrotating functionally graded microbeams vary by the power law exponent while for stationaryfunctionally graded microbeams the modeshapes are invariant with respect to the power lawexponent even in the presence of the thermal environment.

In this study, nonlinear vibrations of simply-supported pipes conveying fluid made of multilayer graphene reinforced composite materials have been investigated analytically and based on the Euler-Bernoulli beam theory. The constituent layers of the pipe wall thickness are considered to be made of polymer and graphene platelets and the reinforcing graphene platelets are varied by layers in the pipe wall thickness direction. Four different patterns for distribution of reinforcing graphene platelets, large deformations, and Von-Karman nonlinear strain field are considered. The nonlinear governing equations are derived by the Hamilton principle, they are converted to the ordinary differential equations by the Galerkin method and then are solved analytically using the homotopy analysis method. The variations of the first nonlinear natural frequency of the system with respect to the variation of initial amplitude, fluid velocity, fluid density, pipe length, and also time response of the nonlinear vibrations of the system are presented for different distribution patterns V, X, O and U of the graphene platelets. The results show that the first nonlinear natural frequency of the system for all distribution patterns of graphene platelets is decreased by an increase of pipe length, fluid velocity, and density but increasing the initial amplitude increases the first nonlinear natural frequency and also the distribution pattern V has the highest nonlinear frequency comparing with the other distribution patterns.

The thin-walled beams are widely adopted in different structural components ranging from civil engineering to aeronautical applications due to their conspicuous characteristics. A slender thin-walled beam loaded initially in compression may buckle suddenly in flexural–torsional mode since its torsional strength is much smaller than bending resistance. In this paper, flexural-torsional stability and free vibration analyses of axially functionally graded tapered I-beam resting on Winkler elastic foundation are assessed. Considering the coupling between the flexural displacements and the twist angle, the motion equations are derived via Hamilton’s principle in association with Vlasov’s thin-walled beam theory. The differential quadrature method is applied to solve the system of differential equations and to acquire the critical buckling loads and natural frequencies. To validate the obtained results, at first, homogeneous tapered I-beam in the absence of elastic foundation was analyzed and compared with a finite element solution using ANSYS and other available benchmarks. Afterward, the numerical outcomes for axially graded non-prismatic I-beam resting on elastic foundation are reported in graphical form to find out the impacts of axial load position, beam’s length, end conditions, web and flanges tapering ratio, material gradient index, Winkler parameter and spring position on the non-dimensional buckling loads and vibration frequencies.

In this paper an efficient and accurate solution method is developed for transient analysis and free vibration of functionally graded truncated conical shell, subjected to symmetric internal or external moving pressure. The material properties of the shell are graded continuously in the radial direction according to a Mori-Tanaka and volume fraction power-law distribution. A hybrid solution method composed of the layerwise theory, differential quadrature method, and Fourier series expansion is employed to investigate the aforementioned problem. A Fourier series expansion is used for the displacement components and dynamic pressure in the axial direction. Then the layerwise theory across the thickness direction in conjunction with the Hamilton’s principle is employed to obtain equations of motion and boundary conditions. Eventually, the differential quadrature method is implemented to discretize the governing equations in the time domain. This research shows some interesting results that can be helpful for design of functionally graded shells subjected to moving pressure. The developed results are successfully compared with the available results in the literature. The convergence study demonstrate the fast convergence rate with relatively low computational cost. The results reveal that a free vibration with significant amplitude is generated due to excitation from transition of the moving pressure. Also increasing the area of moving pressure in the case of constant load magnitude leads to reducing in the magnitudes of displacements and stresses components.

In the current study, the problem of two-dimensional heat conduction in a truncated hollow cone made of functionally graded materials is referred and an exact analytical solution is presented. Functionally graded materials are materials with special production processes in which different thermophysical properties can be gradually changed. In the present study, the properties of a material are modified in accordance with a power function. The thermal boundary conditions are also assumed to be non-homogeneous. The separation of variable (SOV) method is implemented to acquire the exact steady-state temperature distribution. The obtained solution is adequately verified using numerical data. To further demonstrate the ability of the solution, an illustrative case which is exposed to a combination of boundary conditions is studied. In particular, the influences of effective parameters on the temperature distribution are investigated for the current geometry. It is shown that by using functionally graded material more flexible attitudes in terms of temperature distribution are seen. The outcome of this study would be helpful to shed light on the process of designing and optimizing relatively complex geometries. Also, considering the analyticity of the present solution, the results of this study can be useful for a better understanding of the heat transfer mechanisms of functionally graded materials. In the present case, increasing the amount of m and κ, the thermal conductivity increased by about 8 and 2 percent respectively, which would increase the distribution of cone temperature.

Todays, hydrogels have attracted many researchers due to their unique properties in responding to exterior stimuli and swelling-induced by water absorption. According to their reversible swelling, it is important to predict their mechanical response. The functionally-graded temperature-sensitive hydrogel is one of the most applicable materials in industry. Thus, to study the mechanical behavior of these materials, an energy density function is introduced which includes network stretch energy and mixing part. Then, considering functionally-graded properties along the thickness, bending of FG temperature-sensitive hydrogels is solved analytically under plane-strain assumption. Verifying the presented analytical procedure, the results are compared with outcomes of finite-element-method. To solve diverse problems by finite-element-method, UHYPER subroutine has been written and verified in free-swelling problem. Next, the radius, radial stress and tangential stresses are studied by both methods for FG temperature-sensitive hydrogels. Finally, according to the importance of factors such as semi-angle and bending curvature in the industrial designs, these factors are investigated by changing the temperature in range of 320 to 288. Results demonstrate the capability of these material to be implemented in sensors and actuators. In addition, the continuity of stresses field is the other reason of utilizing FG hydrogels, while the multi-layer hydrogels do not have continuous stress fields.