• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.11
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• pp.1835-1843
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• 2001

The energy release rate for an interface crack in anisotropic dissimilar materials was obtained by the eigenfunction expansion method and also was analyzed numerically by the reciprocal work contour integral method. It was shown that the results for orthotropic dissimilar materials are consistent with the other worker's results.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.384-388
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• 2001

The higher order singularities[1] are systematically examined, and discussed are their complementarity relation with the nonsingular eigenfunctions and their relations to the configurational forces like J-integral and M-integral. By use of the so-called two state conservation laws(Im and Kim[2]) or interaction energy, originally proposed by Eshelby[3] and later treated by Chen and Shield[4], the intensities of the higher order singularities are calculated, and their roles in elasticplastic fracture are investigated. Numerical examples are presented for illustration.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.155-160
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• 2001

This paper describes a probabilistic fracture mechanics (PFM) analysis based on Monte Carlo (MC) simulation. In the analysis of CANDU pressure tube, it is necessary to perform the PFM analyses based on statistical consideration of flaw generation time. A depth and an aspect ratio of initial semi-elliptical surface crack, a fracture toughness value, delayed hydride cracking (DHC) velocity, and flaw generation time are assumed to be probabilistic variables. In all the analyses, degradation of fracture toughness due to neutron irradiation is considered. Also, the failure criteria considered are plastic collapse, unstable fracture and crack penetration. For the crack growth by DHC, the failure probability was evaluated in due consideration of flaw generation time.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.627-632
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• 2000

Developing turbulent flows in a rotating 90 degree bend with square cross-section were measured by a hot-wire anemometer. The six orientation hot-wire technique was applied to measured the distributions of 3 mean velocities and 6 Reynolds stress components. Effects of Coriolis and centrifugal forces caused by the curvature and rotation of bend on the mean motion and turbulence structures were experimentally investigated Productive addition of Coriolis and centrifugal forces to the outward radial direction in the entrance region of bend increases the secondary flow intensity according to the rotational speeds. However, after 45 degree of bend, centrifugal force due to the rotation of bend may promote the break down of counter rotating vortex pair into multi-cellular pattern, thereby decreasing the production rate of turbulence energy and Reynolds stresses.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1030-1035
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• 2003

The nanoimprint lithography technology makes higher density of semiconductor device and larger capacity of storage media. In this technology the induced damage while detaching polymer pattern from mold should be minimized. In order to analyze the problem, the basic knowledge of adhesion between the polymer and the mold is required. In this study a contact experiment of polyisobutylene specimen with spherical steel tip and polyisobutylene bead tip was conducted using nano indenter. During the contact experiment with various loading rate under load control the contact behavior of viscoelastic material was measured, i.e., the load and displacement between the tip and the specimen were measured. The data was analyzed by HBK model to obtain the stress intensity factor of contact edge and the contact radius as a function of time. Also the adhesion energies between steel/polyisobutylene and polyisobutylene/polyisobutylene were obtained employing the analysis of the crack of viscoelastic material by Schapery.

• Advanced Composite Materials
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• v.16 no.1
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• pp.11-30
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• 2007

Since delamination often propagates at the interfacial layer between a surface skin and a foam core, a crack arrester is proposed for the suppression of the delamination. The arrester has a semi-cylindrical shape and is arranged in the foam core and is attached to the surface skin. Here, energy release rates and complex stress intensity factors are calculated using finite element analysis. Effects of the arrester size and its elastic moduli on the crack suppressing capability are investigated. Considerable reductions of the energy release rates at the crack tip are achieved as the crack tip approached the leading edge of the crack arrester. Thus, this new concept of a crack arrester may become a promising device to suppress crack initiation and propagation of the foam core sandwich panels.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.2
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• pp.185-193
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• 1996

Errors included in solutions obtained by the boundary element method are generally larger than those by the finite element method in the case that the number of discreted elements is small. One of the reasons is supposed to be attributed to the error which will be produced in the numerical integration of the singular functions in two dimensional elastic problem. Then, treatment of analytical integration to reduce computing time and to decrease errors of boundary element method are proposed.

• Journal of the Korean Society for Precision Engineering
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• v.9 no.3
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• pp.61-66
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• 1992

This paper addresses on the determination of damping coefficients of an infinitely long squeeze film damper operating with an electro-rheological (ER) fluid. The ER fluid behaves as Bingham fluid with an electric field dependent yield shear stress. AS phenomenological model of the fluid is adopted for the relationship between the yield shear and the intensity of the electric field imposed on the fluid domain. The model is then incorporated with the governing equation and associated boundary conditions of the squeeze film damper executing a circula centered orbit for the expression of dimension- less damping coefficients. Numerical simulation is performed to evaluate the performance improvement of the proposed squeeze film damper.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1386-1388
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• 2003

In this study. the fatigue behavior of cracked aluminum repaired by unidirectional graphite/epoxy composites was experimentally investigated. The aluminum used was 7075-T6 and the patch used was four plied unidirectional ([0]$_4$) composites. The composite patch was adhesively bonded to the cracked aluminum using secondary bonding procedure. Two different specimens of cracked aluminum and cracked aluminum repaired with patch were used in the fatigue tests. Load ratio and the frequency applied in the fatigue tests were 0 and 10 Hz, respectively. The results showed that the fatigue behavior of cracked aluminum was improved by repairing the cracked area with composite patch. Specifically, the specimen repaired by composite patch showed 30% more improved fatigue behavior than regular specimen.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1530-1537
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• 1991

본 연구에서는 반무한 직선 계면균열의 상하면에 임의로 분포하는 어떠한 하 중에 대해서도 그 해석이 가능한 그린함수(Green's function)를 구하고자 한다. 이 를 위하여 반무한 직선 계면균열상의 임의의 한 점에 평면 집중하중이 작용하는 문제 와 비평면 집중전단하중이 작용하는 문제를 각각 택하였고, 이때 계면균열의 선단은 열려있다고 가정하였다. 이 문제를 풀므로써 균열선단부근의 응력성분을 결정하고 이로부터 그린함수의 의미를 지니는 응력강도계수에 대한 폐형해를 얻었다.