• Journal of the Korean Society of Safety
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• v.15 no.2
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• pp.8-12
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• 2000

The fatigue crack propagation tests were performed in triangular and holding-time stress waveforms at $650^{\circ}C$. The behavior of fatigue crack propagation was investigated according to waveform. The analysis of high temperature fatigue crack propagation by the stress intensity factor range ${\Delta}K$, elastic fracture mechanics parameter, was not available. The behaviors of high temperature fatigue crack propagation by the J-integral(${\Delta}J_f$, J' and ${\Delta}J_c$), elasto-plastic fracture mechanics parameter, were investigated in a number of stress waveforms. The fast-fast waveform exhibited cycle-dependent(fatigue type), the slow-fast and the hold time with 500sec waveforms appear to be time-dependent(creep type) and the fast-slow and the hold time with 5, 25sec waveforms exhibited conbined behavior of both types(fatigue-creep conbined type).

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.6
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• pp.938-945
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• 2012

This research proposes FEM analysis for Tandem welding process used in wind tower and predicts optimal welding process to improve the stability of welded structures. Three dimensional elasto-plastic analyses are employed to evaluate thermo-mechanical behavior of residual stress and deformation during Tandem welding for different distance between two touches. To confirm the thermal distribution, Goldak's ellipse heat source model and the real size wind tower pipe model are utilized. Four different analyses are being performed, where in each case the distance between two electrode torches is being changed and residual stress and welding deformation are predicted. Depending on base material state, each case is divided into: Liquid (100mm), Austenite+Liquid (200mm), Austenite+Cementite (400mm), Pearlite+Cementite (800mm).

• Computational Structural Engineering
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• v.2 no.1
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• pp.55-64
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• 1989

A procedure which may be useful in dealing with problems of half plane is considered. Boundary elements are combined with nonlinear finite elements to facilitate their merits. Boundary elements for semi-infinite region are composed using the Melan's solution for half plane. Nonlinear finite elements are used to model irregularity or nonhomogeneity of elasto-plastic materials, which is usual in underground structures. In order to verify the procedure, a shallow tunnel under internal pressure is analysed using the nonlinear finite element method and combined method. It is shown that the developed procedure is accurate enough compared with other method.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.773-777
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• 2011

본 논문에서는 국부적으로 비선형 거동을 보이는 고전적인 $J_2$ 소성흐름 이론에 근거한 탄소성 문제의 해를 효율적으로 구하기 위해 전체-국부 확장함수를 지닌 일반유한요소법을 제안한다. 제안된 기법은 비선형 거동을 보이는 영역을 포함하는 국부 문제의 비선형 해를 구하고 이를 일반유한요소법의 단위 오목 분할의 개념을 통해 전체 문제의 해 공간을 확장하는데 이용한다. 이는 적은 계산량으로 복잡한 탄소성문제의 정확한 해를 얻는 것을 가능하게 하며 기법의 강건성과 정확성을 입증하기 위한 수치해석 예제가 다루어진다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.04a
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• pp.95-101
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• 2001

Steel bridges, which have been damaged by load and corrosion, need repair or strengthening. In general, before the repair welding procedure, cutting procedure carry out. Therefore, the investigating of the behavior of stress generated by cutting is so important for safety of structure. Residual stress produced by gas cutting was analyzed using 2D and 3D thermal elasto-plastic FEM. According to the results, the magnitude of temperature was analyzed by 2D-FEM is smaller than that was analyzed using the 3D-FEM program at the start and end edge of flange. And the magnitude and distribution of residual stress of perpendicular to the cutting line was analyzed by the 2D-FEM program was similar to that was analyzed by the 3B-FEM program. Therefore, it is possible to predict of cutting stress by 2D and 3D FEM.

• Journal of Welding and Joining
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• v.18 no.5
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• pp.33-40
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• 2000

Fatigue crack propagation life of weld toe crack through residual stress field was estimated with Elber's crack concept. Propagation of weld toe crack is heavily influenced by residual stress caused by welding process, so it is essential to take into account the effect of residual stress on the propagation life of weld toe crack. Fatigue crack at transverse and longitudinal weld toe was studied respectively, which represent typical weld joint in ship structure. Numerical and experimental studies are performed for both cases. Residual stress near weldment was estimated through nonlinear thermo-elasto-plastic finite element method, and residual stress intensity factor with Glinka's weight function method. Effective stress intensity factor was calculated with Newman-Forman-de Koning-Henriksen equation which is based on Dugdale strip yield model in estimating crack closure level U at different stress ratio. Calculated crack propagation life coincided well with experimental results.

• Journal of Welding and Joining
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• v.31 no.2
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• pp.43-48
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• 2013

This paper Investigated the characteristics of residual stress in weld is composed of typical specimens, are investigated by using three dimensional thermal elasto-plastic FEM analysis. Numerically calculated residual stresses in the gas welds were then compared with experimental results obtained by the hole-drilling method. Using the stress amplitude (${\sigma}a$)R at the hot spot point of gas weld, the relations obtained as the fatigue test results for typical specimens having various dimensions and shapes were systematically rearranged to obtain the (${\sigma}a$)R-Nf relationship. It was found that more systematic and accurate evaluation of the fatigue strength of plug- and ring-type gas-welded joints can be achieved by using (${\sigma}a$)R.

• Journal of Ocean Engineering and Technology
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• v.20 no.4 s.71
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• pp.17-23
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• 2006

Monotonic four-point bending tests were conducted on straight pipe specimens, 102 mm in diameter with local wall thinning, in order to investigate the effects of the depth, shape, and location of wall thinning on the deformation and failure behavior of pipes. The local wall thinning simulated natural erosion/corrosion metal loss. The deformation and fracture behavior of the straight pipes with local wall thinning was compared with that of non wall-thinning pipes. The failure modes were classifiedas local buckling, ovalization, or crack initiation, depending on the depth, shape, and location of the local wall thinning. Three-dimensional elasto-plastic analyses were carried out using the finite element method. The deformation and failure behavior, simulated by finite element analyses, coincided with the experimental results.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1997.04a
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• pp.53-60
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• 1997

The strain localization of concrete is a phenomenon such that the deformation of concrete is localized in finite region along with softening behavior. The objective of this paper is to develope a consistent algorithm for the finite element modeling of localized zone in the analysis of the strain-localization in concrete. For modeling of the localized zone in concrete under strain localization, a general Drucker-Prager failure criterion which can consider nonlinear strain softening behavior of concrete after peak-stress is introduce. The return-mapping algorithm is used for the integration of the elasto-plastic rate equation and the consistent tangent modulus is derived. Using finite element program implemented with the developed algorithms, strain localization behaviors for the different sizes of concrete specimen under compression are simulated.

• Proceedings of the Korea Concrete Institute Conference
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• 1991.10a
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• pp.87-92
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• 1991

It was achieved to formulate numerically the stress-strain relationship of concrete, which is a fundamemtal factor for the Elasto-Plastic analysis of concrete structures, for normal concrete by using random statistics. As a result of experiment, in the shape of stress-strain curves of normal concrete it has approach linear from first loading to peak point, and after that point deformation increased radically and specimens were brokendown abruptly. From the multiple linear regression, and obtained the exponential equaion for stress-strain relationship of concrete as follows: $\sigma$/$\sigma$max=e(1-$\varepsilon$/$\varepsilon$max)$\varepsilon$/$\varepsilon$max