• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.244-249
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• 2002

The purpose of this study is to develope the prediction method of liquation crack initiation in HAZ of laser weldment. Thermal two dimensional strain analyses were performed by FEM for bead-on-plate welding in order to obtain the plastic strain at elevated temperature in HAZ of the laser weldment. From these results, it became clear that the plastic strain at elevated temperature affected liquation crack initiation in HAZ, and it could be proposed that the critical strain, which controlled liquation crack initiation, existed. Moreover, an attempt was made to develop thermal and dynamic three dimensional strain analysis method for the laser weldment in order to obtain the plastic strain at elevated temperature in HAZ of the laser weldment in more detail and precisely.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1995년도 가을 학술발표회 논문집
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• pp.334-338
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• 1995

In recent years, the prediction of the deterioration rate of concrete structures has become major research interest. However, there are still many uncertain factors in the deterioration process and the relation between deterioration and durability of structures. This is mainly due to various uncertainties involved in the construction process and the environmental conditions which affect the rate of deterioration of concrete structures. In this study a limit state model in terms of random crack width due to applied dead and live loads is proposed for the assessment of crack damage of reinforced concrete structures. The AFOSM reliability method is used for the reliability evaluation of the crack durability of concrete bridges. The proposed model for crack durability of concrete bridges is applied to the Seoul interior circuit elevated expressway. The sensitivity analyses are performed for the proposed model.

• Journal of Mechanical Science and Technology
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• 제17권5호
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• pp.647-653
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• 2003

An important class of short-fiber reinforced composites is the sheet molding compound, which is recently developed and currently used in many engineering applications. Fatigue failure of the composites is a subject of major concern in design and cyclic crack propagation is of particular significance in the fatigue life prediction of short fiber composites. However, research on the fatigue behavior of polymer injection weld, especially short glass fiber-filled polymer injection weld, has not been carried out. In this study the analyses of the fatigue crack growth behaviors at weld line and in the bulk are performed based on low cycle fatigue test.

• Journal of Advanced Marine Engineering and Technology
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• 제30권4호
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• pp.494-504
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• 2006

It is well known that the two-parameter $J-A_2$ solution can well characterize the crack-tip fields and quantify the crack-tip constraint for different flawed geometries in variety of loading conditions. However, this solution fails to do so for bending dominated specimens or geometries at large deformation because of the influence of significant global bending stress on the crack-tip field. To solve this issue, a modified $J-A_2$ solution is developed in this paper by introducing an additional term to address the global bending influence. Using the $J_2$ flow theory of plasticity and within the small-strain framework detailed finite element analyses are carried out for the single edge notched bend (SENB) specimen with a deep crack in A533B steel at different deformation levels ranging from small-scale Yielding to large-scale Yielding conditions. The numerical results of the crack-tip stress field are then compared with those determined from the $J-A_2$ solution and from the modified $J-A_2$ solution at the same level of applied loading Results indicate that the modified $J-A_2$ solution largely improves the $J-A_2$ solution, and match very well with the numerical results in the region of interest at all deformation levels. Therefore, the proposed solution can effectively describe the crack-tip field and the constraint for bending dominated specimens or geometries.

• 대한기계학회논문집A
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• 제34권1호
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• pp.19-26
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• 2010

본 논문에서는 유한요소 해석을 통해 용접부 중앙에 원주방향균열이 있는 배관에 대한 강도불일치 한계하중 해석 및 파괴역학 해석을 수행하였다. 강도불일치 한계하중식을 제시하기 위해 강도불일치 비, 용접부 폭, 균열 길이 및 배관 반경비에 대한 체계적인 변수 해석을 수행하였으며 참조응력법을 바탕으로 스테인리스강 및 페리틱 강에 대한 J-적분 계산을 수행하였다. 본 연구에서 제시한 강도불일치 한계하중을 사용하여 참조응력을 정의할 때, 보다 정확한 J-적분 결과를 얻을 수 있었다.

• Computers and Concrete
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• 제12권3호
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• pp.261-283
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• 2013

This paper aims to contribute to the three-dimensional generalization of numerical prediction of crack propagation through the formulation of finite elements with embedded discontinuities. The analysis of crack propagation in two-dimensional problems yields lines of discontinuity that can be tracked in a relatively simple way through the sequential construction of straight line segments oriented according to the direction of failure within each finite element in the solid. In three-dimensional analysis, the construction of the discontinuity path is more complex because it requires the creation of plane surfaces within each element, which must be continuous between the elements. In the method proposed by Chaves (2003) the crack is determined by solving a problem analogous to the heat conduction problem, established from local failure orientations, based on the stress state of the mechanical problem. To minimize the computational effort, in this paper a new strategy is proposed whereby the analysis for tracking the discontinuity path is restricted to the domain formed by some elements near the crack surface that develops along the loading process. The proposed methodology is validated by performing three-dimensional analyses of basic problems of experimental fractures and comparing their results with those reported in the literature.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2219-2227
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• 2002

In a nuclear power plant, reactor pressure vessel (RPV) is the primary pressure boundary component that must be protected against failure. The neutron irradiation on RPV in the beltline region, however, tends to cause localized damage accumulation, leading to crack initiation and propagation which raises RPV integrity issues. The objective of this paper is to estimate the integrity of RPV under hot leg leaking accident by applying the finite element analysis. In this paper, a parametric study was performed for various crack configurations based on 3-dimensional finite element models. The crack configuration, the crack orientation, the crack aspect ratio and the clad thickness were considered in the parametric study. The effect of these parameters on the maximum allowable nil-ductility transition reference temperature ($(RT_{NDT})$) was investigated on the basis of finite element analyses.

• 대한기계학회논문집A
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• 제25권2호
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• pp.275-282
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• 2001

The reactor pressure vessel is usually cladded with stainless steel to prevent corrosion and radiation embrittlement. Number of subclad cracks may be found during an in-service-inspection due to the presence of cladding. It is specified, in ASME Sec. XI, that a subclad crack is characterized as a surface crack when the thickness of the clad is less than 40% of the crack depth. This condition is provided to keep the crack integrity evaluation conservative. In order to refine the fracture assessment procedures for such subclad cracks under a pressurized thermal shock condition, three dimensional finite element analyses are applied for various subclad cracks existing under cladding. A total of 36 crack geometries are analyzed, and the results are compared with those for surface cracks. The resulting stress intensity factors for subclad cracks are 6 to 44% less than those for surface cracks. It is proven that the flaw characterization condition as specified in ASME Sec. XI can be overly conservative for some subclad cracks.

• Computers and Concrete
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• 제13권4호
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• pp.569-585
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• 2014

In this paper, a four-layer road structure consisting of an edge transverse crack is simulated using three-dimensional finite element method in order to capture the influence of a single-axle wheel load on the crack propagation through the asphalt concrete layer. Different positions of the vehicular load relative to the cracked area are considered in the analyses. Linear elastic fracture mechanics (LEFM) is used for investigating the effect of the traffic load on the behavior of a crack propagating within the asphalt concrete. The results obtained show that the crack front experiences all three modes of deformation i.e., mode I, mode II and mode III, and the corresponding stress intensity factors are highly affected by the crack geometry and the vehicle position. The results also show that for many loading situations, the contribution of shear deformation (due to mode II and mode III loading) is considerable.

• 한국가스학회지
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• 제4권4호
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• pp.25-33
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• 2000

최근 들어 가혹한 온도 및 압력조건에서 운전이 요구되는 고온배관들의 잔여수명예측은 상당히 중요한 관심사로 부각되고 있다. 이에 고온손상을 정량적으로 평가하여 설비를 안전하게 사용하기 위한 유지기술 및 수명평가 기술을 확보하는 것은 매우 중요하다. 한편 이러한 고온배관내 대부분의 균열은 반타원 표면균열의 형태로 형상화되어 파괴역학의 실제응용에서 발견할 수 있는 가장 복잡한 형상과 하중특성을 갖게 된다. 이를 배경으로 본 연구에서는 먼저 축방향 및 원주방향 반타원 표면균열이 존재하는 직관의 완전 3차원 유한요소망 자동생성 프로그램을 작성하였다. 이렇게 생성된 유한요소 입력자료를 이용하여 3차원 유한요소 해석을 수행하면 반타원 표면균열선단을 따른 고온 크리프 파괴 지배변수 $C^{\ast}$-적분값을 구할 수 있다. 또한 $C^{\ast}$-적분값에 준해 균열진전량을 계산하는 후처리 균열진전 모듈을 추가하여 사용자 편의 수명평가 프로그램을 개발하였다. 최종적으로 개발된 통합 수명 평가 프로그램을 이용하여 여러 가지 해석변수들의 반타원 표면균열을 갖는 고온 직관 수명에 대한 영향을 살펴보았다.