• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.5
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• pp.47-57
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• 2000

In this study, a fundamental approach to make clear the mechanism of the mutual interference and coalescence of stress fields in the vicinity of two crack tips on the process of their slow growth, using boundary element method. Automatic generation of quadratic discontinuous elements along both of the crack boundaries which can be defined by an arbitrary piece-wise straight geometry. The direction of the crack-extension increment is predicted by the maximum principal stress criterion, corrected to account for the discreteness of the crack extension. Along the computed direction, the crack is extended one increment. Automatic incremental crack-extension analysis with no remeshing, computation of the stress intensity factors by J-integral. Numerical stress intensity factors for two growing cracks in plane-homogeneous regions were determined.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1998.05a
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• pp.89-97
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• 1998

In this study, under large scale yielding conditions crack propagation is found to governed by parameters based on the J-integral or on the crack opening displacement. But initiation of crack propagation of ductile material seems to be controlled by just on parameter that is the strain. The relationship between the critical value of J-integral and the local fracture strain in uniaxial tensile test in the region of maximum reduction in area. Therefore, the fundamental theorectical equation by the proposed elastic-plastic fracture toughness and the local fracture strain has a merit. in comparison with the ASTM method, which can measure by using the load-displacement curve and the specimens in tenslie test.

• Journal of Mechanical Science and Technology
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• v.16 no.9
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• pp.1033-1039
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• 2002

Partial penetration welding joint refers to the groove weld that applies to the one side welding which does not use steel backing and to both side welding without back gouging, that is, the partial penetration welding joint leaves an unwelded portion at the root of the welding area. In this study, we analyzed the residual stress and fracture on the thick metal plates that introduced the partial penetration welding method. According to the above-mentioned welding method, we could draw a conclusion that longitudinal stress and traverse stress occurred around the welding area are so minimal and do not affect any influence. We also performed the fracture behavior evaluation on the partial penetration multi pass welding with 25.4 mm thick plate by using the J-integral, which finally led us the conclusion that the partial penetration multi-pass welding method is more applicable and effective in handling the root face with less than 6.35 mm.

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.25-33
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• 1998

In this study, under large scale yielding conditions crack propagation is found to governed by parameters based on the J-integral or on the crack opening displacement. But initiation of crack propagation of ductile material seems to be controlled by just on parameter that is the strain. The relationship between the critical value of J-integral and the local fracture strain in uniaxial tensile test in the region of maximum reduction in area. Therefore, the fundamental theoretical equation by the proposed elastic-plastic fracture toughness and the local fracture strain has a merit, in comparison with the ASTM method, which can measure by using the load-displacement curve and the specimens in tensile test.

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.41-48
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• 1998

In this paper, an investigation was performed on the dynamic interlaminar fracture toughness of CFRP(carbon fiber reinforcement plastics) composite laminates. Composite laminates used in this experimentation are CF/EPOXY and CF/PEEK laminated plates. In the experiments, Split Hopkinson's Bar(SHPE) test was applied to dynamic and notched flexure test. The mode Ⅱ fracture toughness of each unidirectional CFRP was estimated by the analyzed deflection of the specimen and J-integral with the measured impulsive load and reactions at the supported points. As an experimental result, the vibration amplitude of CF/PEEK laminates appear more than that of CF/EPOXY laminates for the J-integral and displacement velocity at a measuring point. Also, it is thought that the dynamic fracture toughness of two kind specimens(CFRP/EPOXY and CF/PEEK) with the in crease of displacement velocity becomes a little greater at a measuring point within the range of measurement.

• Structural Engineering and Mechanics
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• v.44 no.5
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• pp.601-609
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• 2012

Effect of different crack sizes on fracture criterion of some engineering materials was investigated in this work. Using finite element (FE) method coupled with a newly developed algorithm, J-integral values for different crack sizes were obtained for single-edge notched bend (SENB) and compact type (CT) specimen. Specimens with initial a/W ratio from 0.25 to 0.75 varying in crack size in steps of 0.125 were investigated. Several different materials, like 20MnMoNi55, 42CrMo4 and 50CrMo4, usually used in engineering structure, were investigated. For one of mentioned materials, numerical results were compared with experimental and their compatibility is visible.

• Structural Engineering and Mechanics
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• v.58 no.2
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• pp.217-230
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• 2016

Effects of temperature dependent material properties on mixed mode fracture parameters of functionally graded materials subjected to thermal loading are investigated. A domain form of the $J_k$-integral method including temperature-dependent material properties and its numerical implementation using finite element analysis is presented. Temperature and displacement fields are calculated using finite element analysis and are used to compute mixed mode stress intensity factors using the $J_k$-integral. Numerical results indicate that temperature-dependency of material properties has considerable effect on the mixed-mode stress intensity factors of cracked functionally graded structures.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.330-337
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• 1995

For a rotating body with cracks, the new energy release rate equation is presented. The derived equation is different from the other researcher's results. It is a path-independent integral which excluded the derivatives of displacements near the crack tip, thereby improving the numerical accuracy of the energy release rate computation. Moreover, as the equation was derived on basis of the energy principle and non-linear elasticity without assumptions, it can applied to the cracked body with arbitrary shape under elastic-plastic deformation. Several examples are treated to demonstrate the efficiency and accuracy of the proposed method compared to existing methods.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.3
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• pp.270-277
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• 1983

Plastic plane stress solutions are given for a center cracked strip, characterized by the Ramberg-Osgood plastic index, under bi-axial tension. Using a power law hardening stress-strain relation, an incremental plasticity finite element formulation is developed, and simple formulation is given for computing J-integral with nodal displacements. The near tip angular distribution of von Mises effective stress doesn't differ significantly in magnitude according to the change of loading stress and bi-axial load combination factor. But, for smaller plastic index, the location of its maximum value moves vertically at a head of crack. J-integral value, in the plastic zone near crack tip, decreases with load combination factor for large and small plastic index.

• Selected Papers of The Society of Naval Architects of Korea
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• v.1 no.1
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• pp.4-14
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• 1993

A natural and an artificial harbor can exhibit frequency (or period) dependent water surface oscillations when excited by incident waves. Such oscillations in harbors can cause significant damages to moored ships and adjacent structures. This can also induce undesirable current in harbor. Many previous investigators have studied various aspects of harbor resonance problem. In the present paper, both a localized finite element method(LFEM) which is based on the functional constructed by Chen & Mei(1974) and Bai & Yeung(1974) and an integral equation method which was used by Lee(1969) are applied to harbor resonance problem. The LFEM shows computationally more efficient than the integral equation method. Our test results show a good agreement compared with other results. In the present computations, specifically two harbor geometris are treated here. The present method by LFEM can be extended to a fully three dimensional harbor problem.