• 한국안전학회지
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• 제22권1호
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• pp.19-23
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• 2007

The aim of this study was to determine residual stresses in thermal barrier coatings(TBCs) by isothermal heating. Specimens were heated at the range of $1000{\sim}1600^{\circ}C$. A finite element method was used to determine the residual stresses. Finite element coupled heat transfer and elastic-plastic thermal stress analysis using a general purpose commercial FEM software ABAQUS. I obtained the stresses were not affected below the temperature of $1400^{\circ}C$ but affected over that of temperature.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.326-329
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• 2000

Study of Weldment fracture behavior mcludes thermal analysis, residual stress analysis, and fracture analysis The 1-integral loses its path-independency in a res~dual stress field Therefore, it id necessary to develop a program to calculate the J-integral in a welded plate. m this study, theoretical formulation and program were developed for the evaluation of the 1-integral at the crack tip o i weldments. To verify equations and program, welded thin plate and thick plate were used to calculate residual stress and the J-integral.

• 대한기계학회논문집A
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• 제27권6호
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• pp.987-996
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• 2003

The structural integrity of the reactor vessel with the approaching end of life must be assured for pressurized thermal shock. The regulation specifies the screening criteria for this and requires that specific analysis be performed for the reactor vessel which is anticipated to exceed the screening criteria at the end of plant life. In case the screening criteria is exceeded by the deterministic analysis, probabilistic analysis must be performed to show that failure probability Is within the limit. In this study, probabilistic fracture mechanics analysis of the reactor vessel for pressurized thermal shock is performed and the effects of residual stress and master curve on the failure probability are investigated.

• 전기전자학회논문지
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• 제24권4호
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• pp.1011-1016
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• 2020

We propose a framework called Stacked Gated Recurrent Unit - Infrequent Residual Analysis (SG-IRA) that detects anomalies in time-series data that can be trained on streams of raw sensor data without any pre-labeled dataset. To enable such unsupervised learning, SG-IRA includes an estimation model that uses a stacked Gated Recurrent Unit (GRU) structure and an analysis method that detects anomalies based on the difference between the estimated value and the actual measurement (residual). SG-IRA's residual analysis method dynamically adapts the detection threshold from the population using frequency analysis, unlike the baseline model that relies on a constant threshold. In this paper, SG-IRA is evaluated using the industrial control systems (ICS) datasets. SG-IRA improves the detection performance (F1 score) by 5.9% compared to the baseline model.

• 한국항공우주학회지
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• 제30권2호
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• pp.46-51
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• 2002

홀 확장법은 홀 주위에 압축 잔류응력 층을 생성시킴으로서 균열 발생을 지연시키는 방법으로 항공산업 분야에서 널리 사용되고 있다. 홀 확장잔류응력의 분포는 홀 확장률, 맨드럴 삽입방향, 재료 물성치 등 여러 가지 홀 확장 파라미터에 따라 달리진다. 홀 확장 잔류응력 층의 정확한 파악이 항공사업의 실제 설계에 있어서 매우 중요함에도 불구하고 이에 대한 연구는 상대적으로 부족하였다. 본 연구에서는 3차원 유한요소해석을 통하여 알루미늄 평판에 홀 확장법을 적용하는 경우의 잔류응력 분포를 예측하고자 하였다. 유한요소해석의 타당성을 검증하기 위하여 스트레인 게이지를 이용한 홀 확장 잔류변형률을 측정하였으며, 홀 확장률과 2단 홀 확장이 잔류응력 분포에 미치는 영향을 파악하였다. 2단 홀 확장을 적용함으로써 최대 압축 잔류응력의 크기가 약 7% 향상됨을 알 수 있었다.

• 대한기계학회논문집A
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• 제34권4호
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• pp.413-421
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• 2010

본 연구에서는 실제 용접 과정을 모사하는 유한요소 해석을 이용하여 강도 불일치를 가지는 매설 천연가스 배관 용접부의 잔류응력 분포를 계산한다. 유한요소 해석 절차의 타당성을 검증하기 위해 온도 및 잔류응력 해석 결과들은 실제 용융부 형상과 API 579 적용 결과와 비교된다. 기계적 강도 차이, 용접 금속의 강도, 덧살 및 입열량 등과 같은 용접 및 재료 변수들이 잔류응력 분포에 미치는 영향을 평가하기 위해 Parametric Study가 수행된다. 최종적으로 Parametric Study 결과에 근거하여 용접 및 재료 변수들의 영향이 고찰된다. 특히, 모재들 사이의 강도 불일치는 잔류응력 분포에 미미한 영향을 미침을 확인하였다.

• Steel and Composite Structures
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• 제44권2호
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• pp.199-210
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• 2022

This study build finite element analysis (FEA) models describing the bending events of coiled tubing (CT) at the wellhead and trips into the hole, accurately provide the state of stress and strain while the CT is in service. The bending moment and axial force history curves are used as loads and boundary conditions in the diametrical growth models to ensure consistency with the actual working conditions in field operations. The simulation diametrical growth results in this study are more accurate and reasonable. Analysis the factors influencing fatigue and diametrical growth shows that the internal pressure has a first-order influence on fatigue, followed by the radius of the guide arch, reel and the CT diameter. As the number of trip cycles increase, fatigue damage, residual stress and strain cumulatively increase, until CT failure occurs. Significant residual stresses remain in the CT cross-section, and the CT exhibits a residual curvature, the initial residual bending configuration of CT under wellbore constraints, after running into the hole, is sinusoidal. The residual stresses and residual bending configuration significantly decrease the buckling load, making the buckling and buckling release of CT in the downhole an elastic-plastic process, exacerbating the helical lockup. The conclusions drawn in this study will improve CT models and contribute to the operational and economic success of CT services.

• Steel and Composite Structures
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• 제18권4호
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• pp.985-1000
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• 2015

The method of cross-section analysis for different sections in a structural frame has been widely investigated since the 1960s for determination of sectional capacities of beam-columns. Many hand-calculated equations and design graphs were proposed for the specific shape and type of sections in pre-computer age decades ago. In design of many practical sections, these equations may be uneconomical and inapplicable for sections with irregular shapes, leading to the high construction cost or inadequate safety. This paper not only proposes a versatile numerical procedure for sectional analysis of beam-columns, but also suggests a method to account for residual stress and geometric imperfections separately and the approach is applied to design of high strength steels requiring axial force-moment interaction for advanced analysis or direct analysis. A cross-section analysis technique that provides interaction curves of arbitrary welded sections with consideration of the effects of residual stress by meshing the entire section into small triangular fibers is formulated. In this study, two doubly symmetric sections (box-section and H-section) fabricated by high-strength steel is utilized to validate the accuracy and efficiency of the proposed method against a hand-calculation procedure. The effects of residual stress are mostly not considered explicitly in previous works and they are considered in an explicit manner in this paper which further discusses the basis of the yield surface theory for design of structures made of high strength steels.

• Nuclear Engineering and Technology
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• 제54권7호
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• pp.2550-2563
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• 2022

This study performed a precise dynamic finite element time history elastic-plastic seismic analysis considering the welds, which have been not considered in design stage, on the nuclear components subjected to severe seismic loadings such as beyond-design basis earthquakes for sustainable nuclear power plants. First, the dynamic finite element elastic-plastic seismic analysis was performed for a general design practice that does not take into account the welds of the pressurizer surge line system, one of safety class I components in nuclear power plants, and then the reference values for the accumulated equivalent plastic strain, equivalent plastic strain, and von Mises effective stress were set. Second, the dynamic finite element elastic-plastic seismic analyses were performed for the case of considering only the mechanical strength over-mismatch of the welds as well as for the case of considering both the strength over-mismatch and welding residual strain. Third, the effects of the strength over-mismatch and welding residual strain were analyzed by comparing the finite element analysis results with the reference values. As a result of the comparison, it was found that not considering the strength over-mismatch may lead to conservative assessment results, whereas not considering the welding residual strain may be non-conservative.

• Nuclear Engineering and Technology
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• 제52권8호
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• pp.1862-1870
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• 2020

The purpose of this study is to investigate the effect of welding residual stress on operating stress in designing a nuclear turbine welded rotor. A two-dimensional axisymmetric finite element model is employed to calculate the residual stress before and after post weld heat treatment (PWHT), and then the superposition of residual stress after PWHT and operating stress at normal speed and overspeed were discussed. The investigated results show that operating stress can be affected significantly by welding residual stress, and the distribution trend of superposition stress at the weld area is mainly determined by welding residual stress. The superposition of residual stress and operating stress is linear superposition, and the hoop stress distribution of superposition stress is similar with the distribution of residual stress. With the increasing overspeed, the distribution pattern of the hoop superimposed stress remains almost unchanged, while the stress level increases.