• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.94-97
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• 2008

In the welding process, weldments usually include repair weld during the manufacturing process. Repair welds is supposed to cause strong tensile residual stress. Moreover weldments, usually made by Alloy 82/182, is susceptible to PWSCC. Therefore, mitigation of welding residual stress in weldments is important for reliable operating. PWOL is one of the methods for mitigation and verified for over twenty years. In this paper, residual stress distribution of repaired weldments and the effect of PWOL on mitigation is examined for surge nozzle.

• 한국전산구조공학회논문집
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• 제22권6호
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• pp.557-564
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• 2009

용접과정 중 발생되는 인장잔류응력은 원전 배관 이종용접부의 PWSCC가 발생되는 원인 중 하나라고 알려져 있다. 일반적으로 보수용접은 용접과정 중 흔히 일어나는 현상이다. 보수용접은 강한 인장잔류응력을 유도하기 때문에 이종용접부의 PWSCC를 유도하기 쉽다. 본 논문에서는 강한 인장잔류응력이 발생되는 보수용접부에 대해 보수용접 깊이에 따라 동종용접과 예방용접 overlay로 인하여 인장잔류응력의 크기가 변화하는 것을 정량적으로 확인하였다.

• Smart Structures and Systems
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• 제29권4호
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• pp.589-598
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• 2022

Timber structures are susceptible to structural damages caused by variations in moisture content (MC), inducing severe durability deterioration and safety issues. Therefore, it is of great significance to detect MC levels in timber structures. Compared to current methods for timber MC detection, which are time-consuming and require bulky equipment deployment, Lead Zirconate Titanate (PZT)-enabled stress wave sensing combined with statistic machine learning classification proposed in this paper show the advantage of the portable device and ease of operation. First, stress wave signals from different MC cases are excited and received by PZT sensors through active sensing. Subsequently, two non-baseline features are extracted from these stress wave signals. Finally, these features are fed to a statistic machine learning classifier (i.e., naïve Bayesian classification) to achieve MC detection of timber structures. Numerical simulations validate the feasibility of PZT-enabled sensing to perceive MC variations. Tests referring to five MC cases are conducted to verify the effectiveness of the proposed method. Results present high accuracy for timber MC detection, showing a great potential to conduct rapid and long-term monitoring of the MC level of timber structures in future field applications.

• 대한기계학회논문집A
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• 제32권10호
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• pp.873-881
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• 2008

Weld overlay is one of the residual stress mitigation methods which arrest crack initiation and crack growth. Therefore weld overlay can be applied to the region where cracking is likely to be. An overlay weld used in this manner is termed a preemptive weld overlay(PWOL). In pressurized water reactor(PWR) dissimilar metal weld is susceptible region for primary water stress corrosion cracking(PWSCC). In order to examine the effect of PWOL on residual stress mitigation, PWOL was applied to a specific dissimilar metal weld of Kori nuclear power plant by finite element analysis method. As a result, strong compressive residual stress was made in PWSCC susceptible region and PWOL was proved effective preemptive repair method for weldment.

• Journal of Welding and Joining
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• 제33권2호
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• pp.40-46
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• 2015

This study was performed to investigate the effect of ultrasonic nano crystal surface modification (UNSM) on residual stress mitigation after Weld Inlay repair for butt dissimilar metal weld with Alloy 82/182 in reactor vessel In/Outlet nozzle. As-welded and Weld Inlay specimens were made in accordance with design standard of ASME Code Case N-766, and two planes of their weld specimens were peened by the optimum UNSM process condition. Peening characteristics for weld specimens after UNSM treatment were evaluated by surface roughness and Vickers hardness test. And, residual stress for weld specimens developed from before and after UNSM treatment was measured and evaluated by instrumented indentation technique. Consequently, it was revealed that the mitigation of residual stress in weld metal after Weld Inlay repair of reactor vessel In/Outlet nozzle could be possible through UNSM treatment.

• Nuclear Engineering and Technology
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• 제51권5호
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• pp.1451-1469
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• 2019

This paper proposes a residual stress mitigation of a nuclear safety-related austenitic stainless steel TP304 pipe bended by local induction heating process via performing elastic-plastic finite element analysis. Residual stress distributions of the pipe bend were calculated by performing finite element analysis. Validity of the finite element analysis procedure was verified via comparing with temperature histories measured by using thermocouples, ultrasonic thickness measurement results, and residual stress measurement results by a hole-drilling method. Parametric finite element stress analysis was performed to investigate effects of the process and geometric shape variables on the residual stresses on inner surfaces of the pipe by applying the verified procedure. As a result of the parametric analysis, it was found that it is difficult to considerably reduce the inner surface residual stresses by changing the existing process and geometric shape variables. So, in order to mitigate the residual stresses, effect of an additional process such as cooling after the bending on the residual stresses was investigated. Finally, it was identified that the additional heating after the bending can significantly reduce the residual stresses while other variables have insignificant effect.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2009년도 정기 학술발표대회
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• pp.162.2-162.2
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• 2009

• 한국방재학회 논문집
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• 제8권2호
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• pp.97-103
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• 2008

Determination of stress-strain relationship in torsional tests is complicated due to nonuniform stress-strain variation occurring linearly with the radius in a soil specimen in torsion. The equivalent radius approach is adequate when calculating strain at low to intermediate strains, however, the approach is less accurate when performing the test at higher strain levels. The modified equivalent radius approach was developed to account for the problem more precisely. This approach was extended to generate the plots of equivalent radius ratio versus strain using modified hyperbolic and Ramberg-Osgood models. Results showed the effects of soil nonlinearity on the equivalent radius ratio curves were observed. Curve fitting was also performed to find the stress-strain relationship by fitting the theoretical torque-rotation relationship to measured torque-rotation relationship.

• 한국방재학회 논문집
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• 제1권1호
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• pp.117-125
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• 2001

비활성 그리고 황성 단층지역의 내부와 주변에서 발생하는 응력장의 변화에 대한 수치적 분석이 수행되었다. 존재하는 비활성 단층지역 근처에서의 응력장은 단층의 방향과 단층화된 암반과 주위의 비단층화된 암반의 탄성적 특성 사이의 대조에 따라 변화한다. 활성 단층지역 주위의 응력장에 대한 분석에서, 만약 단층지역의 항복응력이 초과된다면, 단층지역 내에서의 국부화된 전단응력은 주위의 비단층화된 암반에서의 평균응력 보다 작게 되는 단층 내에서의 평균응력의 감소를 유발시킨다. 따라서 이러한 응력경사는 단층지역내로 유체의 흐름을 기대할 수 있다.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2009년도 정기 학술발표대회
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• pp.162.1-162.1
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• 2009