• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.106-112
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• 1996

In this paper, the propagation of elastic wave generated by loading impact to plates made of isotropic or anisotropic material was studied. And the influence of boundary conditions(free or clamped edge) upon the reflection of elastic wave of isotropic plate such as aluminum plate showed circular interferometric fringe pattern, whereas that of anisotropic plate such as epoxy composite laminates showed elliptical one. And the transverse displacement curves obtained from experiment and theory for both plates agreed well. Also, the waves reflected from the boundary edges showed much differences according to the boundary condition of edges.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.10
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• pp.3211-3223
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• 1996

In this paper, the propagation of elastic wave generated by loading impact to plates made of isotropic of anisotropic material was studied. And the influence of boundary conditions (free or clamped edge) upon the reflection of elastic wave was anlyzed. Also, double exposure holographic interferometer using ruby pulse laser was formed in order to investigate transient waves. Before the elasitc wave was reflected from the edges, the elastic wave of isotropic plate such as aluminum plate showed circular interferometric fringe pattern, whereas that of anisotropic plate such as epoxy composite laminates showed elliptical one. And the transverse displacement curves obtained from experiment and theory for both plates agreed well. Also, the waves reflected from the boundary edges showed much differences according to the boundary condition of edges.

• Steel and Composite Structures
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• v.42 no.4
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• pp.427-446
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• 2022

Cutouts in the beams or plates are often unavoidable due to inspection, maintenance, ventilation, structural aesthetics purpose, and sometimes to lighten the structures. Therefore, there will be a substantial reduction in the strength of the structure due to the introduction of the cutouts. However, these cutouts can be reinforced with the different patterns of ribs (stiffener) to enhance the strength of the structure. The present study highlights the influence of the elliptical cutout reinforced with a different pattern of ribs on the stability performance of such stiffened composite panels subjected to non-uniform edge loads by employing the Finite element (FE) technique. In the present formulation, a 9-noded heterosis element is used to model the skin, and a 3-noded isoparametric beam element is used to simulate the rib that is attached around a cutout in different patterns. The displacement compatibility condition is employed between the plate and stiffener, and arbitrary orientations are taken care by introducing respective transformation matrices. The effect of shear deformation and rotary inertia are incorporated in the formulation. A new mesh configuration is developed to house the attached ribs around an elliptical cutout with different patterns. Initially, a study is performed on the panels with different stiffener schemes for various ply orientations and for different stiffener depth to width ratios (d_s/b_s) to determine an optimal stiffener configuration. Further, various parametric studies are conducted on an obtained optimal stiffened panel to understand the effect of cutout size, cutout orientation, panel aspect ratio, and boundary conditions. Finally, from the analysis, it can be observed that the arrangement of the stiffener attached to a panel has a major impact on the buckling capacity of the stiffened panel. The stiffener's depth to width ratio also significantly influences the buckling characteristic.

• Transactions of the Korean Society of Mechanical Engineers
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• v.5 no.2
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• pp.82-87
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• 1981

이 논문에서는 타원형의 크랙을 포함하는 유한한 두께을 가진 isotropic탄성체의 삼차원응력해석을 다루었다. 크랙은 평판의 면에 나란하고 그 중립면에 위치하며 일정한 인장력이 평판의 면에 작용하고 있다. 문제를 해석하기 위하여 이중 Fourier 적분변환을 사용하여 응력해석이 제 일종 Fredholm 적분 방정식의 해로 될 수 있음을 보였다. 두 극한의 경우 즉(i) 평판의 두께가 무한한 경우와 (ii) 타원이 원으로 reduce 되는 경우에 기존의 해와 일치됨을 보였다. 적분 방정식의 해 빛 응력해석은 제 이장에서 다루기로 한다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.5 no.4
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• pp.312-319
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• 1981

이 논문에서는 제1장에서 유도한 제일종 Fredholm 적분방정식에 대하여 근사해를 해석적인 방법에 의하여 구하였으며 이 근사해를 사용하여 응력확대계수(S.I.F.)와 크랙에너지를 산출하였다. 또한 이 연구에서는 크랙경계 근처에서의 이차원응력치가 크랙끝에서 크랙에 수직한 평면내에서 정의된 좌표 s 와 .theta.의 값으로 표시될 수 있음을 보였다.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.190-196
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• 2014

In this paper, the characteristics of a defective elliptical aluminum plate are analyzed by three different eddy current testing probes; T/R, T/T, and Impedance probes. The analysis was done by 3D finite element method, and the impedance change of real and imaginary voltage values were analyzed.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.4
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• pp.575-581
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• 2013

In this paper, we experimentally investigated the effects of attached cylindrical tripwires on the aerodynamic performance. The research was carried out with a simple two-dimensional (2-D) rectangular airfoil fabricated from thin flat-plate aluminium, with elliptical leading and trailing edges. Tripwires of varying widths and thicknesses, and attack angles of $-5^{\circ}{\sim}20^{\circ}$ were used to investigate the aerodynamic characteristics (e.g. lift and drag forces) of the airfoil. We found that attaching the tripwires to the lower surface of the airfoil enhanced the lift force and increased the lift-to-drag ratio for low attack angles. However, attaching the tripwires to the upper surface tended to have the opposite effects. Moreover, we found that attaching the tripwires to the trailing edge had similar effects as a Gurney flap. The aerodynamic characteristics of the flat-plate airfoil with tripwires can be used to develop passive control devices for aircraft wings in order to increase their aerodynamic performance when gliding at low attack angles.

• Journal of Mechanical Science and Technology
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• v.15 no.4
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• pp.413-421
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• 2001

A simple procedure to add and remove material simultaneously along the boundary is developed to optimize the shape of a two dimensional elastic problems and to minimize the maximum von Mises stress. The results for the two dimensional infinite plate with a hole, are close to the theoretical results of an elliptical boundary and the stress concentration is reduced by half for the fillet problem. The proposed shape optimization method, when compared with existing derivative based shape optimization methods has many features such as simplicity, applicability, flexibility, computational efficiency and a much better control on stresses on the design boundary.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.2
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• pp.141-144
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• 1984

The fatigue limits of crack initiation and propagation on the edge elliptical notched semi-infinite plate under completely reversed fatigue stress are determined theoretically. Assuming that the crack initiation and propagation occur when stress intensity factors of notched plate reach the critical values obtained from critical micro-crack length under plain fatigue limit loading and the threshold stress intensity factory, respectively, the fatigue limits of crack initiation and propagation are obtained. The induced theoretical fatigue limit of crack initiation is expressed in terms of plain fatigue limit, critical micro-crack length and notch shape. The one of crack propagation is in terms of threshold stress intensity factor, plain fatigue limit and notch shape. These theoretical results are showed to be in good agreement of Frost's experimental data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.6
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• pp.916-922
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• 1986

This paper presents the preliminary results of an experimental study on surface crack growth under fatigue loadings. The objective of this paper is to assess the effect of the initial crack size on crack propagation behaviors. Transparent PMMA plate speciments with shallow circular arc notch were used. Crack growth behaviors were observed and measured in two directions by travelling microscopes. The fatigue crack initiated at the deepest part on the initial arc shaped notch and then propagated to depth direction as well as spreading gradually along the notch tip. A considerable number of cycles was needed until the depth crack spreaded to the surface notch tip. When the fatigue crack reached the surface notch tip the crack front became an approximate semi-ellipse, primary semi-elliptical crack. Test results suggest that the relationships between fatigue crack growth rate and stress intensity factor range in both directions can be expressed by power law (Paris) and that relationship in width direction depends upon the crack ratios a$_{1}$/b$_{1}$, of the primary semi-elliptical crack. The relationship between the nondimensional crack lengths in both directions can be represented as the formula: (a/t)$^{n}$ =B(2b/W+A) where n and A are constants and B is seems to be depended upon the crack ratio a$_{1}$/b$_{1}$.