• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.9
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• pp.2138-2144
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• 1993

An integral equation representation of cracks was presented which differs from well-known "dislocation layer" representation. In this new representation, the equations are written in terms of the displacement discontinuity across the crack surfaces rather than derivatives of the displacement-discontinuity. It was shown in that the new technique is well-suited to the treatment of kinked cracks. In the present paper, this integral equation representation is coupled to the direct boundary-element method for the treatment of finite bodies containing kinked cracks. The method is demonstrated for two-dimensional finite domains but extension to three-dimensional problems would appear to be possible. The resulting approach is shown to be simple, yet very accurate. accurate.

• Journal of Welding and Joining
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• v.18 no.3
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• pp.68-75
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• 2000

The incomplete penetration(IP) discontinuity in butt joint weld, which is detected during safety analysis of the steel bridge by nondestructive evaluation(NDE) method, is classified as unacceptable defect according to the NDE codes and standards. In fact, there are a little allowance in butt joint weld in the view point of design criterion, and also detected IP discontinuity should be classified and evaluated for the fatigue strength and residual life estimation. In this study, we performed fatigue test to evaluate the fatigue strength of high strength steel(SWS490A) containing IP discontinuities in various size, the results compared and classified according to the bridge construction standard specification which published by korea administration of construction and traffic. Experimental results could be used to evaluate and estimate the IP discontinuities considering different stress range in butt joint bridge weld during periodic safety inspection.

• Journal of Welding and Joining
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• v.21 no.6
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• pp.71-76
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• 2003

For the purpose of clarifying the influence of welding residual stress to the fatigue crack propagations behaviour, an analytical investigation based on finite element method is performed to examine the opening behaviour of tip-closed crack in the compressive residual stress. A finite element model comprised of contact elements for the crack plane and plane stress elements for the base material is used to evaluate crack opening stress of the crack existing in the residual stress field. Also an analytical method based on the superposition principle to estimate the length of opened part of tip closed crack and the stress distribution adjacent to the crack during uploading is applied to the finite element model. The software for the analysis is ABAQUS, which is a general purpose finite element package. The results show that stresses distributed on the crack surfaces are reduced and approached to zero as the applied stresses are increased up to crack tip opening stress and no mechanical discontinuity is found at the boundary of contact elements and plane stress elements. It is verified that the opening behavior of the fatigue crack in the residual stress can be predicted by finite element method with the proposed analytical method.

• Transactions of the Korean Society of Mechanical Engineers
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• v.6 no.4
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• pp.361-366
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• 1982

This paper attempts to predict the stress concentration around the corner of rectangular inserts of different material of mechanical properties from the base material of the finite rectangular plate. The problem is analyzed through the FEM and photo-elastic experiment with the inclination angle of the insert as variable parameters. According to the experiments and the numerical analysis, the maximum stress concentration occurs at the point of tangential discontinuity of a insert. When the lain insert or opening was so inclined that the distance from the free end of the plate to a corner became minimum, the maximum stress concentration factor was found.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.1
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• pp.170-180
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• 1995

A parallel crack in bonded dissimilar orthotropic planes under out-of-plane loading is analyzed. The problem is formulated by Fourier integral transforms, and reduced to a pair of dual integral equations. By solving the integral equations, the asymptotic stress and displacement fields near the crack tip are determined in closed form, from which the stress intensity factor and energy release rate are obtained. Discontinuity in the stress intensity factor as the distance ratio h/a of the parallel crack approaches zero is found, while the energy releas rate is shown to be continuous at h/a = 0. This information can immediately be used to generate the stress intensity factor for the parallel crack near the interface. By employing "the maximum energy release rate criterion", it could be shown in the case of no existing crack initially that the parallel crack is formed far from the interface for the more compliant material, while it is formed close to the interface for the stiffer material. material.

• Computers and Concrete
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• v.4 no.4
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• pp.259-272
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• 2007

A method based on the lower-bound theorem of limit analysis is presented for the capacity assessment of nodal zones in strut-and-tie models. The idealized geometry of the nodal zones is formed by the intersection of effective widths of the framing struts and ties. The stress distribution is estimated by dividing the nodal zones into constant stress triangles separated by lines of stress discontinuity. The strength adequacy is verified by comparing the biaxial stress field in each triangle with the corresponding failure criteria. The approach has been implemented in a computer-based strut-and-tie tool called CAST (Computer-Aided Strut-and-Tie). An application example is also presented to illustrate the approach.

• Journal of the Korean GEO-environmental Society
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• v.19 no.12
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• pp.25-32
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• 2018

This paper investigates the effect of rock discontinuities on a shear stress wave that is induced by earthquake or blasting and provides the result of numerical parametric studies. The numerical tests of different conditions of rock and discontinuity have been carried out after confirming that the numerical approach is valid throughout a verification analysis from which the test results were compared with a theoretical solution. In-situ stress condition was considered as a rock condition and internal friction angle and cohesive value, which are the shear strength parameters, were considered as discontinuities condition. The joint inclination angle was also taken into account as a parameter. With the various conditions of different parameters, the test results showed that a shear stress wave propagating through a mass is highly influenced by the shear strength of discontinuities and the condition of joint inclination angle as well as in-situ stress. The study results indicate that when earthquake or blasting-induced dynamic loading propagates through a jointed rock mass or a stratified soil ground the effect of in-situ stress and discontinuities including a stratum boundary should be taken into account when evaluating the dynamic effect on nearby facilities and structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.3
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• pp.447-456
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• 1997

Stress intensity factor of semi-infinite parallel crack propagation with constant velocity in dissimilar orthotropic strip under out-of-plane clamped desplacement is investigated. Using Fourier integral transforms the boundary value problem is derived by a pair of dual integral equation and finally reduced to a single Wiener-Hopf equation. By applying Wiener-Hopf technique the equation is solved. Applying this result the asymptotic stress fields near the crack tip are determined, from which the stress intensity factor is obtained in closed form. The more the ratio of anisotropy or the ratio of bi-material shear modulus increase in the main material including the crack, the more the stress intensity factor increases. Discontinuity in the stress intensity factor is found as the parallel crack approaches the interface. In special case, the results of isotropic materials agree well with those by the previous researchers.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.359-370
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• 1993

Up to now, most studies are on interface crack problems in isotropic-isotropic dissimilar materials, but it seems to be not so much on anisotropic dissimlar materials. In this study, the stress intensity factors for an interface crack in anisotropic dissimilar materials are analysed using author's proposed extrapolation method by BEM and we have done a parametric study about material properties or shapes of crack affecting to the stress intensity factors. However, as there are not other's comparable numerical results on these anisotropic dissimilar materials to the best of author's knowledge, the reliability of the present results was proved by following two methods. The first is considering the asymptotic characteristic about stress intensity factors for an interface crack in anisotropic materials when the ansiotropic material approachs to the isotropic material. The second is considering the discontinuity of stress intensity factors between of a crack in an identical homogeneous anisotropic material and an interface crack in anisotropic dissimilar materials.

• Proceedings of the KWS Conference
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• 2003.11a
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• pp.179-181
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• 2003

The present study focuses on the effect of geometrical discontinuity, strength mismatch, which can elevate plastic constraint due to heterogeneous plastic straining, and loading rate on the ductile crack initiation using two-parameter criterion. Fracture initiation testing has been conducted under static and dynamic loading using circumferentially notched round-bar specimens. In order to evaluate the stress/strain state in the specimens, especially under dynamic loading, a thermal elastic-plastic dynamic finite element (FE) analysis considering the temperature rise due to plastic deformation has been carried out.