• Smart Structures and Systems
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• v.26 no.5
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• pp.641-656
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• 2020

The finite element solutions of thermal buckling load values of the graded sandwich curved shell structure are reported in this research using a higher-order kinematic model including the shear deformation effect. The numerical buckling temperature has been computed using an in-house specialized code (MATLAB environment) prepared in the framework of the current mathematical formulation. In addition, the mathematical model includes the excess structural distortion under the influence of elevated environment via Green-Lagrange nonlinear strain. The corresponding eigenvalue equation has been solved to predict the critical buckling temperature of the graded sandwich structure. The numerical stability and the accuracy of the current solution have been confirmed by comparing with the available published results. Thereafter, the model is extended to bring out the influences of structural parameters i.e. the curvature ratio, core-face thickness ratio, support conditions, power-law indices and sandwich types on the thermal buckling behavior of graded sandwich curved shell panels.

• Journal of Korean Physical Therapy Science
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• v.23 no.1
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• pp.1-8
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• 2016

Purpose : The purpose of this study was to investigate the response of pulmonary function and heart rate recovery of smoker and nonsmoker in males aged 20s after graded maximal exercise. Method : The subjects were composed of smoker group (n=12) and nonsmoker group (n=12) in males aged 20s. Each groups completed an graded maximal exercise with Bruce protocol and were assessed on the pulmonary function(forced vital capacity : FVC, forced expiratory volume-one second : FEV1, FEV1/FVC) and heart rate. Result : The results were as follows: First, heart rate in the measurement point was a statistically significant difference for smoker and non-smoker group after maximal exercise, but FVC, FEV1, FEV1/FVC was no difference. Second, FEV1/FVC between smoker and nonsmoker group was a statistically significant difference after maximal exercise, but FVC, FEV1, heart rate was no difference. Conclusion : The results of this study is that smoking is negative effects on FEV1/FVC of pulmonary function in males aged 20s after maximal exercise.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.285-287
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• 2014

Equations of motion for the vibration analysis of rotating pre-twisted beams with functionally graded material properties are derived in this paper. Based on Timoshenko beam theory, the effects of shear and rotary inertia are considered. The pre-twisted beam has a rectangular cross-section and is mounted on a rotating rigid hub with a setting angle. Functionally graded material (FGM) properties are considered along the height direction of the beam. The equations of stretching and bending motion are derived by Kane's method employing hybrid deformation variables. To validate the derived equations, natural frequencies of a rotating FGM pre-twisted beam are compared to those obtained by a commercial software ANSYS. The effects of the pre-twisted angle, slenderness ratio, hub radius, volume fraction exponent, and angular speed on the modal characteristics of the system are investigated with the proposed model.

• Smart Structures and Systems
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• v.9 no.5
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• pp.427-439
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• 2012

The present paper deals with the analytical solution of a functionally graded piezoelectric (FGP) cylinder in the magnetic field under mechanical, thermal and electrical loads. All mechanical, thermal and electrical properties except Poisson ratio can be varied continuously and gradually along the thickness direction of the cylinder based on a power function. The cylinder is assumed to be axisymmetric. Steady state heat transfer equation is solved by considering the appropriate boundary conditions. Using Maxwell electro dynamic equation and assumed magnetic field along the axis of the cylinder, Lorentz's force due to magnetic field is evaluated for non homogenous state. This force can be employed as a body force in the equilibrium equation. Equilibrium and Maxwell equations are two fundamental equations for analysis of the problem. Comprehensive solution of Maxwell equation is considered in the present paper for general states of non homogeneity. Solution of governing equations may be obtained using solution of the characteristic equation of the system. Achieved results indicate that with increasing the non homogenous index, different mechanical and electrical components present different behaviors along the thickness direction. FGP can control the distribution of the mechanical and electrical components in various structures with good precision. For intelligent properties of functionally graded piezoelectric materials, these materials can be used as an actuator, sensor or a component of piezo motor in electromechanical systems.

• Macromolecular Research
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• v.11 no.4
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• pp.236-240
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• 2003

Fabrication of a graded index profile was possible via photochemical reaction of cinnamoyl groups with 350 nm wavelength UV light to form crosslinked structures. Such structural change may induce the change in the refractive index. In order to generate graded index profile in the PMMA polymer optical fiber (POF) with cinnamoyl groups by photochemistry, a methyl methacrylate monomer containing a cinnamoyl functional group in the side chain were prepared. This monomer was then copolymerized with methyl methacrylate with various compositions not only to utilize advantages of poly(methyl methacrylate) but also to overcome the drawbacks of the cinnamate homopolymer. Changes of refractive indices were investigated with various contents of cinnamoyl group and varying irradiation time. Large change in the refractive index (${\Delta}{\approx}0.01$) and its proper profile shape ($g{\approx}2.2$) can be obtained by changing irradiation time.

• Structural Engineering and Mechanics
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• v.23 no.1
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• pp.63-74
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• 2006

In this paper, the scattering of harmonic elastic anti-plane shear waves by two collinear cracks in functionally graded materials is investigated by means of nonlocal theory. The traditional concepts of the non-local theory are extended to solve the fracture problem of functionally graded materials. To overcome the mathematical difficulties, a one-dimensional non-local kernel is used instead of a two-dimensional one for the anti-plane dynamic problem to obtain the stress field near the crack tips. To make the analysis tractable, it is assumed that the shear modulus and the material density vary exponentially with coordinate vertical to the crack. By use of the Fourier transform, the problem can be solved with the help of a pair of triple integral equations, in which the unknown variable is the displacement on the crack surfaces. To solve the triple integral equations, the displacement on the crack surfaces is expanded in a series of Jacobi polynomials. Unlike the classical elasticity solutions, it is found that no stress singularities are present at crack tips.

• Advances in Computational Design
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• v.3 no.2
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• pp.165-190
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• 2018

In this article, the static behavior of non-prismatic sandwich beams composed of functionally graded (FG) materials is investigated for the first time. Two types of beams in which the variation of elastic modulus follows a power-law form are studied. The principle of minimum total potential energy is applied along with the Ritz method to derive and solve the governing equations. Considering conventional boundary conditions, Chebyshev polynomials of the first kind are used as auxiliary shape functions. The formulation is developed within the framework of well-known Timoshenko and Reddy beam theories (TBT, RBT). Since the beams are simultaneously tapered and functionally graded, bending and shear stress pushover curves are presented to get a profound insight into the variation of stresses along the beam. The proposed formulations and solution scheme are verified through benchmark problems. In this context, excellent agreement is observed. Numerical results are included considering beams with various cross sectional types to inspect the effects of taper ratio and gradient index on deflections and stresses. It is observed that the boundary conditions, taper ratio, gradient index value and core to the thickness ratio significantly influence the stress and deflection responses.

• Steel and Composite Structures
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• v.18 no.3
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• pp.659-672
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• 2015

This research deals with the analytical solution of a curved beam with different shapes made of functionally graded materials (FGM's). It was assumed that modulus of elasticity is graded along the thickness direction of curved beam based on a power function. The beam was loaded under pure bending. Using the linear theory of elasticity, the general relation for radial distribution of radial and circumferential stresses of arbitrary cross section was derived. The effect of nonhomogeneity was considered on the radial distribution of circumferential stress. This behavior can be investigated for positive and negative values of nonhomogeneity index. The novelty of this study is application of the obtained results for different combination of material properties and cross sections. Achieved results indicate that employing different nonhomogeneity index and selection of various types of cross sections (rectangular, triangular or circular) can control the distribution of radial and circumferential stresses as designer want and propose new solutions by these options. Increasing the nonhomogeneity index for positive or negative values of nonhomogeneity index and for various cross sections presents different behaviors along the thickness direction. In order to validate the present research, the results of this research can be compared with previous result for reachable cross sections and non homogeneity index.

• Steel and Composite Structures
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• v.18 no.3
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• pp.793-809
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• 2015

In this scientific work, constructing of a novel shear deformation beam model including the stretching effect is of concern for flexural and free vibration responses of functionally graded beams. The particularity of this model is that, in addition to considering the transverse shear deformation and the stretching effect, the zero transverse shear stress condition on the beam surface is assured without introducing the shear correction parameter. By employing the Hamilton's principle together with the concept of the neutral axe's position for such beams, the equations of motion are obtained. Some examples are performed to demonstrate the effects of changing gradients, thickness stretching, and thickness to length ratios on the bending and vibration of functionally graded beams.

• Structural Engineering and Mechanics
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• v.28 no.6
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• pp.695-713
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• 2008

The aim of this contribution is to present a new link/beam finite element suitable for electrothermo-structural analysis of uni-axially graded materials. Continuous polynomial variation of geometry and material properties will be considered. The element matrix and relations for solution of Joule's heat (and its distribution to the element nodes) have been established in the sense of a sequence method of a coupled problem solution. The expression for the solution of nodal forces caused by a continuously distributed temperature field has also been derived. The theoretical part of this contribution is completed by numerical validation, which proves the high accuracy and effectiveness of the proposed element. The results of the performed experiments are compared with those obtained using the more expensive multiphysical link element and solid element of the FEM program Ansys. The proposed finite element could be used not only in the multiphysical analysis of the current paths and actuators but also in analysis of other 1D construction parts made of composite or uni-axially graded materials.