• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.8 s.179
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• pp.2007-2014
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• 2000

It has been reported that the dynamic stress intensity factor for a propagating crack is increasing or decreasing according to the increasement of the crack propagating velocity. It is confirmed in this study that the increasement or decreasement of stress intensity factor with crack growing velocity is accused by loading condition. When the crack propagates under a constant displacement along upper and lower boundary in finite plate, the dynamic stress intensity factor decreases according to the increasement of the propagating crack velocity. When the crack propagates under a constant stress along upper and lower boundary in finite plate, the dynamic stress intensity factor increases according to the increasement of the propagating crack velocity. The increasement or decreasement of stress intensity factor with crack growing velocity is greater in a fast crack propagation velocity than in a slow one.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.3
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• pp.270-275
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• 2013

In this study, focusing of ultrasonic Lamb wave by negative refraction with mode conversion from antisymmetric to symmetric mode was investigated. When a wave propagates backward by negative refraction, the energy flux is antiparallel to the phase velocity. Backward propagation of Lamb wave is quite well known, but the behavior of backward Lamb wave at an interface has rarely been investigated. A pin-type transducer is used to detect Lamb wave propagating on a steel plate with a step change in thickness. Conversion from forward to backward propagating mode leads to negative refraction and thus wave focusing. By comparing the amplitudes of received Lamb waves at a specific frequency measured at different distance between transmitter and interface, the focusing of Lamb wave due to negative refraction was confirmed.

• Journal of Mechanical Science and Technology
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• v.14 no.7
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• pp.752-763
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• 2000

The stress field around the dynamically propagating interface crack tip under a remote mixed mode loading condition has been studied with the aid of dynamic photoelastic method. The variation of stress field around the dynamic interface crack tip is photographed by using the Cranz-Shardin type camera having $10^6$ fps rate. The dynamically propagating crack velocities and the shapes of isochromatic fringe loops are characterized for varying mixed load conditions in double cantilever beam (DCB) specimens. The dynamic interface crack tip complex stress intensity factors, $K_1\;and\;K_2$, determined by a hybrid-experimental method are found to increase as the load mixture ratio of y/x (vertical/horizontal) values. Furthermore, it is found that the dynamically propagating interface crack velocities are highly dependent upon the varying mixed mode loading conditions and that the velocities are significantly small compared to those under the mode I impact loading conditions obtained by Shukla (Singh & Shukla, 1996a, b) and Rosakis (Rosakis et al., 1998) in the USA.

• Journal of the Korean Society of Industry Convergence
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• v.9 no.1
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• pp.37-44
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• 2006

Stress and displacement fields of a Mode III crack propagating along the normal to gradient in an orthotropic functionally gradient materials (OFGM), which has (1) an exponential variation of shear modulus and density, and (2) linear variation of shear modulus with a constant density, are derived. The equations of motion in OFGM are developed and solution to the displacement and stress fields for a propagating crack at constant speed though an asymptotic analysis. The first three terms in expansion of stress and displacement are derived to explicitly bring out the influence of nonhomogeneity. When the FGM constant ${\zeta}$ is zero or $r{\rightarrow}0$, the fields for OFGM are almost same as the those for homogeneous orthotropic material. Using the stress components, the effects of nonhomogeneity on stress components are discussed.

• Bulletin of the Korean Chemical Society
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• v.23 no.2
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• pp.325-329
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• 2002

In this study, the dependency of the behavior of propagating front on the reaction condition in frontal polymerization reaction has been studied. We have used some multifunctional acrylates as a monomer and ammonium persulfate as an initiator for the polymerization reactions. In frontal polymerization, a method of producing polymeric materials via a thermal front that propagates through the unreacted monomer/initiator solution, the behavior of self propagating front shows various dynamic patterns depending on the reaction condition. We have obtained some spin modes of propagating front in the number of 'hot spots' or 'spin heads' by changing the reaction condition. The effect of the reactor tube diameter on the mode of propagating front has also been studied by using some reactor tubes with different size of tube diameter and it has been examined in some detail by adopting an experimental method of two-tubes system.

• Proceedings of the Optical Society of Korea Conference
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• 2009.02a
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• pp.449-450
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• 2009

The spatial coherence and propagation property of laser beam propagating through several optical components were studied experimentally by using the measurement of Wigner distribution function. It is shown experimentally that the Wigner function measurement yields total degree of coherence, beam quality parameter, and the near and the far field information of the propagating beam. More complete characterization of the laser beam was achieved by applying the Schmidt mode decomposition to the Wigner distribution function, spatial coherence function and directional coherence function. Fine details of coherence property are understood by the characteristics of the contributing eigenmodes.

• Composites Research
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• v.18 no.1
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• pp.38-44
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• 2005

In this paper, the group velocity dispersion curves of the $S_o$ symmetric mode in unidirectional CFRP plate was calculated as varying the propagating direction. The group velocity curve was obtained with the group velocities of the $S_o$ symmetric mode corresponding to 0.2 MHz-mm under the first cut-off frequency in the dispersion curves, and corrected by introducing the slowness curve. The velocities of the $S_o$ symmetric mode in the unidirectional CFRP plate were measured as varying the propagating direction and compared with the col?rotted group velocity curve. The measured velocities were good agreement with the corrected group velocity curve except near the fiber direction which was called the cusp region. It implies that the direction of the group velocities incline toward the fiber direction of the unidirectional CFRP plates when the propagation direction is not accorded with the principal axis. It is supposed that this phenomenon rerults from the preferential propagating the energy toward the direction with the faster propagation velocity.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.151-155
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• 2005

Three-dimensional structures of unsteady detonation wave propagating through a square-shaped tube is studied using computational method and parallel processing. Inviscid fluid dynamics equations coupled with variable-${\gamma}$ formulation and simplified one-step Arrhenius chemical reaction model were analysed by a MUSCL-type TVD scheme and four stage Runge-Kutta time integration. Results in three dimension show the two unsteady detonation wave propagating mode, the Rectangular and diagonal mode of detonation wave instabilities. Two different modes of instability showed the same cell length but different cell width and the geometric similarities in smoked-foil record.

• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.15-19
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• 2005

Three-dimensional structures of unsteady detonation wave propagating through a square-shaped tube is studied using computational method and parallel processing. Inviscid fluid dynamics equations coupled with variable-${\gamma}$ formulation and simplified one-step Arrhenius chemical reaction model were analysed by a MUSCL-type TVD scheme and four stage Runge-Kutta time integration. Results in three dimension show the two unsteady detonation wave propagating mode, the Rectangular and diagonal mode of detonation wave instabilities. Two different modes of instability showed the same cell length but different cell width and the geometric similarities in smoked-foil record.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.3 s.246
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• pp.249-259
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• 2006

Stress and displacement fields of a propagating Mode III crack in an orthotropic functionally gradient material (OFGM), which has (1) linear variation of shear modulus with a constant density, and (2) an exponential variation of shear modulus and density, are derived. The equations of motion in OFGM are developed and solution to the displacement and stress fields fer a propagating crack at constant speed though an asymptotic analysis. The stress terms associated with $\gamma^{-1/2}\;and\;\gamma^{0}$ are not affected by the FGM constant $\zeta$ which is nonhomogeneous parameter, only on the higher order terms, the influences of nonhomogeneity on the stress are explicitly brought out. When the FGM constant $\zeta\;is\;zero\;or\;\gamma{\rightarrow}0$, the fields for OFGM are almost same as the those for homogeneous orthotropic material. Using the stress components, the effects of nonhomogeneity on stress components are discussed.