• Korean Journal of Optics and Photonics
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• v.16 no.3
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• pp.239-247
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• 2005

In this study, we have used newly developed dual-beam shearography which is based on laser speckle that includes various information about an object. Among the several shearing techniques, we used Michelson shearing interference technique which is the most powerful. Acrylate plate was used as a sample, which has inner defects and low thermal conductivity. Michelson shearing interferometer was used for obtaining speckle fringes. We also used phase shifting technique to get a phase map. Using single beam illumination, we could obtain mixture of deformation components of both in-plane and out-of-plane. In order to separate the two components, we have used dual-beam shearography technique. We have obtained a speckle pattern of both before and after deformation. Through LS filtering and unwrapping processes, we could find a position and a shape of the inner defects easily. Deformation of the acrylate plate due to thermal heating has occurred mainly in z-direction(out-of-plane) because it has low thermal conductivity. The acrylate plate was deformed only at the restricted area where the electrical heat applied.

• Advances in nano research
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• v.6 no.2
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• pp.113-133
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• 2018

In this work, free vibration characteristics of functionally graded piezoelectric (FGP) nanobeams based on third order parabolic shear deformation beam theory are studied by presenting a Navier type solution as the first attempt. Electro-mechanical properties of FGP nanobeam are supposed to change continuously throughout the thickness based on power-law model. To capture the small size effects, Eringen's nonlocal elasticity theory is adopted. Using Hamilton's principle, the nonlocal governing equations for third order shear deformable piezoelectric FG nanobeams are obtained and they are solved applying analytical solution. By presenting some numerical results, it is demonstrated that the suggested model presents accurate frequency results of the FGP nanobeams. The influences of several parameters including, external electric voltage, power-law exponent, nonlocal parameter and mode number on the natural frequencies of the size-dependent FGP nanobeams is discussed in detail.

• Steel and Composite Structures
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• v.29 no.3
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• pp.349-362
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• 2018

Thermal buckling behavior of porous functionally graded nanobeam integrated with piezoelectric sensor and actuator based on the nonlocal higher-order shear deformation beam theory is investigated for the first time. Its material properties are assumed to be temperature-dependent and varying along the thickness direction according to the modified power-law rule. Note that the porosity with even type is considered herein. The equations of motion are obtained through Hamilton's principle. The influences of several parameters (such as type of temperature distribution, external electric voltage, material composition, porosity, small-scale effect, Ker foundation parameters, and beam thickness) on the thermal buckling of FG nanobeam are investigated in detail.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2270-2276
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• 2002

Dynamic stability of a rotary oscillating cantilever beam is presented in this study. Using the stretch deformation instead of the conventional axial deformation, three linear partial differential equations are derived from Hamilton's principle and transformed into dimensionless forms. Stability diagrams of the first order approximate solutions are obtained by using the multiple scale perturbation method. The stability diagrams show that relatively large unstable regions exist near the combination of the first chordwise bending natural frequency and the first stretch natural frequency. This result is verified by using the generalized -$\alpha$ method.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.194-197
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• 2005

In this work, a mixed beam approach is performed to identify the transverse shear behavior of thin-walled composite beams with closed cross-sections. The analytical model includes the effects of elastic couplings, shell wall thickness, and torsion warping. The distributions of shear flow across the section as well as the shear correction coefficients are obtained in a closed form in the beam formulation. The influence of transverse shear deformation on the static behavior of closed cross-section composite beams is also investigated in the analysis

• Journal of the Korean Society for Precision Engineering
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• v.8 no.4
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• pp.107-117
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• 1991

The dynamic stability problem of nonconservative system is one of the important problems. In this study, flexible missile with mass variation is regarded as a free Timoshenko beam subjected to a controlled follower force. The stability was studied numerically through the finite element method. Through the study, the obtained results are as follows: [1] Without force direction control (1) In the case of no mass reduction, the existence of concentrated mass increases critical follower force. (2) Mass reduction rate of the beam slightly effects on the change of critical follower force. [2] With force direction control (1) Shear deformation parameter S contributes insignificantly to the force at instability when $S{\geq}10^4$. (2) With mass variation, increase of concentrated mass increases critical follower force at instbility. (3) The type of promary instability is determined by the sensor location.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.11
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• pp.3441-3453
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• 1996

A finite element anlaysis is performed for large deformations of a felxible beam. The total Lagrangian formulation for a general large deformation, which involves finite rotations, is chosen and the exponential map is used to treat finite rotations from the Eulerian point of view. The finite elements results are confirmed for several cases of deformations through comparison to a first order elasticity solution obtained by numerical integration, and the agreement between the two is found to be excellent. For lateral buckling, the point of vanishing determinant of the resulting unsymmetric tangent stiffness is traced to examine its relationship to bifurcation points. It is found that the points of vanishing determinant is not corresponding to bifurcation points for large deformation in general, which suggests that the present unsymmetric tangent stiffness is not an exact first derivative of internal forces with respect to displacement.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.6
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• pp.384-390
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• 2015

The vibration analysis of rotating inward beams considering the pre-twisted is presented based on Euler-Bernoulli beam theory. The frequency equations, are calculated using hybrid deformation variable modeling along with the Rayleigh-Ritz assumed mode methods. In this study, resulting system of ordinary differential equations shows the effects of angular speed, and Young's modulus ratio. It is believed that the results will be a reference with which other researchers and commercial FE analysis program, ANSYS can compare their result.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.335-340
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• 2001

Dynamic stability of a rotary oscillating cantilever beam is presented in this study. Using the stretch deformation instead of the conventional axial deformation, three linear partial differential equations are derived from Hamilton's principle and transformed into dimensionless forms. Stability diagrams of the first order approximate solutions are obtained by using the multiple scale perturbation method. The stability diagrams show that relatively large unstable regions exist near the combination of the first chordwise bending natural frequency and the first stretch natural frequency. This result is verified by using the generalized-${\alpha}$ method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.389-391
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• 2014

The Vibration Analysis of Rotating Inward Beams Considering The Tip-Mass is presented based on Euler-Bernoulli beam theory. The frequency equations, which are coupled through gyroscopic coupling terms, are calculated using hybrid deformation variable modeling along with the Rayleigh-Ritz assumed mode methods. In this study, resulting system of ordinary differential equations shows the effects of angular speed, and Young's modulus ratio. It is believed that the results will be a reference with which other researchers and commercial FE analysis program, ANSYS can compare their results.