• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.908-913
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• 2000

In the process of integrity evaluation for nuclear power plant components, a series of fracture mechanics evaluation on surface cracks in reactor pressure vessel(RPV) must be conducted. These fracture mechanics evaluations are based on stress intensity factor, K. However, under pressurized thermal shock(PTS) conditions, the combination of thermal and mechanical stress by steep temperature gradient and internal pressure causes considerably high tensile stress at the inside of RPV wall. Besides, the internal pressure during the normal operation produces high tensile stress at the RPV wall. As a result cracks on inner surface of RPVs may experience elastic-plastic behavior which can be explained with J-integral. In such a case, however, J-integral may possibly lose its validity due to constraint effect. In this paper, in order to verify the suitability of J-integral, two dimensional finite element analyses were applied for various surface crack. Total of 18 crack geometries were analyzed, and Q stresses were obtained by comparing resulting HRR stress distribution with corresponding actual stress distributions. In conclusion, HRR stress fields were found to overestimate the actual crack-tin stress field due to constraint effect.

• Structural Monitoring and Maintenance
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• 제5권1호
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• pp.129-150
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• 2018

This paper presents the structural performance monitoring of an urban footbridge located in Hangzhou, China. The structural health monitoring (SHM) system is designed and implemented for the footbridge to monitor the structural responses of the footbridge and to ensure the structural safety during the period of operation. The monitoring data of stress and displacement measured by the fiber Bragg grating (FBG)-based sensors installed at the critical locations are used to analyze and assess the operation performance of the footbridge. A linear regression method is applied to separate the temperature effect from the stress monitoring data measured by the FBG-based strain sensors. In addition, the static vertical displacement of the footbridge measured by the FBG-based hydrostatic level gauges are presented and compared with the dynamic displacement remotely measured by a machine vision-based measurement system. Based on the examination of the monitored stress and displacement data, the structural safety evaluation is executed in combination with the defined condition index.

• Nuclear Engineering and Technology
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• 제47권7호
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• pp.895-906
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• 2015

Background: Mitigation of primary water stress corrosion cracking (PWSCC) is a significant issue in the nuclear industry. Advanced nickel-based alloys with lower susceptibility have been adopted, although they do not seem to be entirely immune from PWSCC during normal operation. With regard to structural integrity assessments of the relevant components, an accurate evaluation of crack growth rate (CGR) is important. Methods: For the present study, the extended finite element method was adopted from among diverse meshless methods because of its advantages in arbitrary crack analysis. A user-subroutine based on the strain rate damage model was developed and incorporated into the crack growth evaluation. Results: The proposed method was verified by using the well-known Alloy 600 material with a reference CGR curve. The analyzed CGR curve of the alternative Alloy 690 material was then newly estimated by applying the proven method over a practical range of stress intensity factors. Conclusion: Reliable CGR curves were obtained without complex environmental facilities or a high degree of experimental effort. The proposed method may be used to assess the PWSCC resistance of nuclear components subjected to high residual stresses such as those resulting from dissimilar metal welding parts.

• 한국압력기기공학회 논문집
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• 제18권2호
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• pp.54-60
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• 2022

ASME BPVC provides stress evaluation rules for Class 2 and 3 nuclear piping. However, such rules are difficult to be applied to reinforced wall-thinned pipes during service. To resolve this issue, a new method for stress evaluation of reinforced wall-thinned pipes is proposed in this work, based on the equivalent stiffness concept. By converting a reinforced wall-thinned pipe to an equivalent straight pipe having the same stiffness, stress evaluation can be proceeded using the current ASME BPVC rules. The proposed method is applied to pipes with 4 different normal pipe size and the effects of reinforcement and wall-thinning dimensions on evaluated stresses are discussed.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 춘계학술발표대회 개요집
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• pp.396-398
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• 2005

At present, fatigue design of welded structures is primarily based on nominal stress or hot spot stress approach with a series of classified weld S-N curves. However, these methods are known to possess drawbacks, such as difficulty associated with defining proper nominal stress and the finite element sue sensitivity etc. Recently, a mesh-size insensitive structural stress definition is proposed by Battelle that gives a stress state at weld toe with relatively large mesh size. The structural stress definition is based on the elementary structural mechanics theory and provides an effective measure of a stress state in front of weld toe. As an experimental validation of the structural stress method in obtaining the fatigue strength of weldments, a series of experiment is carried out for various sizes of weldments. Based on the result from this study, it is expected to develop a more precise fatigue strength evaluation technique and to save time period required in the fatigue design of ship and offshore structures.

• 콘크리트학회지
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• 제7권2호
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• pp.126-135
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• 1995

온도균열은 시멘트의 수화열에 의한 온도응력이 콘크리트의 인장강도보다 커질 경우에 발생하는 균열로서, 구조물의 수밀성과 기밀성등에 중대한 영향을 미치기 때문에 매스콘크리트와 같이 단면이 큰 구조물의 설계 및 시공시에는 반드시 온도균열에 대한 배려가 필요하다. 본 연구에서는 모의실험체를 대상으로 하여 매스콘크리트의 경화시 발생하는 온도응력을 측정할 목적으로 콘크리트변형계와 무응력계 그리고 유효응력계등을 설치하여구조물 내부의 온도응력의 경시변화를 검토하고 콘크리트변형계를 이용한 온도응력 산정방법 및 문제점등에 대하여 검토하였다. 연구결과 콘크리트변형계와 무응력계를 이용한 새로운 온도응력 산정법을 제시하였으며, 그 결과 유효응력계의 측정치와 거의 일치하는 값을 얻을 수 잇었다. 이를 위해서는 무응력계 또는 이와 동일하게 초기재령시의 콘크리트 자기수축변형률을 측정할 수 있는 게이지의 설치가 전제가 되어야 하며, 초기재령시의 건조수축량에 대한 정량화가 가능하다면 콘크리트변형계를 이용한 온도응력의 산정도 충분히 가능하다는 것을 알 수 있다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제2권4호
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• pp.200-210
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• 2010

In this paper, different evaluation methods of Hot Spot Stresses (HSS) have been applied to four different welded structure details in order to compare them and to illustrate their differences. The HSSs at failure-critical locations were calculated by means of a series of finite element analyses. There was good overall agreement between calculated and experimentally determined HSS on the critical locations. While different methods and procedures exist for the computation of the structural hot-spot stress at welded joints, the recommendations within the International Institute of Welding (IIW) guideline concerning the 'Hot Spot Stress' approach were found to give good reference stress approximations for fatigue-loaded welded joints. This paper recommends and suggests an appropriate finite element modeling and hot spot stress evaluation technique based on round-robin stress analyses and experimental results of several welded structure details.

• 한국기계가공학회지
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• 제2권1호
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• pp.51-56
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• 2003

A custom application system, which was based on the finite element analysis, for stress on the head-skirt junction of a hot pressure vessel was developed. This is useful computer-based analysis system which designed to provide an analysis technique and knowledge conveniently available to other people. It was found the evaluation of thermal stress of several typed skirt joint of a pressure vessel could be performed early using this system.

• 대한기계학회논문집A
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• 제25권4호
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• pp.756-763
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• 2001

In the process of integrity evaluation for nuclear power plant components, a series of fracture mechanics evaluation on surface cracks in reactor pressure vessel(RPV) must be conducted. These fracture mechanics evaluation are based on stress intensity factor, K. However, under pressurized thermal shock(PTS) conditions, the combination of thermal and mechanical stress by steep temperature gradient and internal pressure causes considerably high tensile stress at the inside of RPV wall. Besides, the internal pressure during the normal operation produces high tensile stress at the RPV wall. As a result, cracks on inner surface of RPVs may experience elastic-plastic behavior which can be explained with J-integral. In such a case, however, J-integral may possibly lose its validity due to constraint effect. In this paper, in order to verify the suitability of J-integral, tow dimensional finite element analyses were applied for various surface cracks. A total of 18 crack geometries were analyzed, and $\Omega$ stresses were obtained by comparing resulting HRR stress distribution with corresponding actual stress distributions. In conclusion, HRR stress fields were found to overestimate the actual crack-tip stress field due to constraint effect.

• 대한의용생체공학회:의공학회지
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• 제35권6호
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• pp.197-202
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• 2014

The cognitive rehabilitation training is important for treating many cognitive impairment conditions, including Parkinson's disease, stroke, and ADHD. In this study, we developed a new evaluation system to improve the measurement of the conventional evaluation systems for cognitive rehabilitation training. The developed system measured the activity of dopamine(DA) and an autonomic nervous system(ANS) with photoplethysmography and electromyography. The results demonstrated that the cognitive capacity was increased but the activity of DA was decreased with unbalanced ANS by short-term stress. Based on the results, the effect of short-term stress should be recognized for the cognitive rehabilitation training.