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Bangkok, Thailand

Taeprasartsit S.,Infra Technology Service Co
JVC/Journal of Vibration and Control | Year: 2015

A finite element model of large amplitude free vibrations of thin functionally graded beams with immovably supported ends is developed in this paper. The material properties of functionally graded beams are assumed to vary according to the power law distribution through the thickness direction. The finite element model is formulated in a variationally correct way based on Euler-Bernoulli beam theory and von Karman geometric nonlinearity. The linear exact displacement fields of the static case are used as the shape functions. The time response of each node is assumed to be a harmonic function, and the error residuals due to this assumption are minimized by employing the Galerkin method. Together this assumption and method transform the finite element equations to an eigenvalue equation that can be solved using a direct iterative method in tandem with the principle of energy conservation. The accuracy of the proposed method is demonstrated by comparing the frequencies and amplitudes with those of other methods presented in the literature. Finally, the relation between the frequencies of functionally graded beams and those of the homogeneous beams at various initial amplitudes is also examined. © The Author(s) 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

Taeprasartsit S.,Infra Technology Service Co
International Journal of Computational Methods | Year: 2012

This paper focuses on deriving the exact displacement fields of a functionally graded column (FGC) subjected to mechanical and thermal loads under the assumptions of the Timoshenko beam theory and von Karman strains. Valid only when an axial load is present, the obtained displacement fields are, therefore, not applicable in pure bending analysis. These displacement fields are used as the interpolation functions for formulating static finite element equations whose DOFs are arbitrary constants rather than nodal displacements. The element is super-convergent in von Karman nonlinear analysis, and its superiority over beam elements formulated by using linear exact displacement fields is shown in two examples: (1) the buckling analysis of a stepped FGC, and (2) an FGC subjected to a thermal load. Also investigated is the efficiency of using von Karman nonlinear displacement fields as the interpolation functions for analyzing cases in which the level of nonlinearity is higher than that of the von Karman strain. © 2012 World Scientific Publishing Company.

Taeprasartsit S.,Infra Technology Service Co
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science | Year: 2010

When an appropriate reference plane is used, the coupling between axial and bending deformations in the stiffness matrix of a functionally graded beam (FGB) element vanishes. Then the stiffness matrix of the FGB element reduces to the same form as that of the homogeneous beam element. However, the coupling in the mass matrix of the FGB element cannot be eliminated at the same time. Consequently, in an analysis that does not involve mass, it is possible to use a homogeneous beam element to obtain the same results as would be achieved with an FGB element. This paper focuses on explaining a procedure to use ANSYS's BEAM3 element to analyse FGBs. The BEAM3 element has the ability to deal with a linear temperature gradient that is sufficient to analyse any arbitrary temperature distribution shape through thickness.

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