잔류응력의 영향을 고려한 용접부 내진 평가

김종성(Jong-Sung Kim),장현수(Hyun-Su Jang) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4

BDBE 와 같이 심각한 지진 하중 하에서 원자력 발전소의 안전성을 검증하기 위해 APR-1400의 가압기와 고온관을 연결하는 밀림배관의 탄소성 유한요소 해석을 수행하였다 [1~2]. 이전 연구에서 지진에 중요한 위치인 가압기 노즐과 핫레그 노즐의 용접부 모사할 때 3case (용접부의 기하학적 형상을 고려하지 않은 경우, 기하학적 형상과 용접 물성을 고려한 경우, 잔류응력을 고려한 경우)에 대해서 지진해석을 수행하였다. 잔류응력을 고려하여 지진해석을 수행한 경우, 누적소성변형률과 등가소성변형률이 다른 경우에 비해 상당히 크게 발생하였다. 잔류응력 해석시 용접부가 융착되는 시간은 매우 짧다. 따라서 본 연구에서는 잔류응력을 고려한 지진해석의 누적소성변형률과 등가소성변형률을 좀 더 현실적으로 시뮬레이션 하기 위해서 어닐링 온도를 고려하여 잔류응력 해석을 수행하였다. 용접 재료인 ER308l의 물성은 주기적인 테스트 결과를 가지고 있지 않기 때문에, 간단한 인장 실험의 결과를 통해 샤보세 경화 모델을 정의하였다. 또한 분석 변수(예: 지진 변위 시간 이력)는 이전 연구에 사용하였던 것과 동일한 값을 사용하였다. 잔류응력을 고려한 지진 해석시 핫레그 노즐과 용접부 사이에서 취약부위가 발생하였다. 취약 부위에 대해 ASME code [3]의 변형률 기반 허용 기준 평가를 수행하였고, 무결성이 만족되었다. 어닐링 온도는 잔류응력 해석에 의해 발생한 누적소성변형률과 등가소성변형률에 상당한 영향을 미치고, 그에 따라 잔류응력을 고려한 용접부의 내진 평가 시 여유도에 영향을 미치는 것을 확인하였다. To verify the safety of nuclear power plants under severe seismic loads, such as BDBE, the finite element elastic-plastic analysis of the surge line system connecting the pressurizer and the hot-leg of APR-1400 was conducted. In the previous study, seismic analysis was conducted on 3 cases (not considering geometry shape of weld, considering geometry shape of welds and material properties of welds, considering welding residual stress) when simulating welds in pressurizer nozzles and hot-leg nozzles, which are critical location for earthquakes. When seismic analysis was conducted in consideration of welding residual stress, accumulated plastic strain and equivalent plastic strain were significantly larger than those of other cases. When conducting welding residual stress, the time for weld to fuse is very short. Therefore, in this study, welding residual stress analysis was conducted considering annealing temperature to more realistic simulation of accumulated plastic strain and equivalent plastic strain of seismic analysis considering welding residual stress. The welding material was used as ER308l instead of TP316 which was previously used material. Since the properties of ER308l do not have cyclic test results, define the Chaboche hardening model through the results of a simple tensile experiment. Furthermore, the analytical variables (such as seismic displacement time history) used the same values as those used in previous study. The seismic analysis was conducted considering the effects of welding residual stress, and vulnerable point occurred between hot-leg nozzles and welds. The integrity was satisfied by performing strain-based acceptance criteria evaluation of ASME code. The annealing temperature was confirmed to have a significant effect on the accumulated plastic strain and the equivalent plastic strain caused by welding residual stress analysis. Accordingly, it was confirmed that the seismic evaluation of welds considering welding residual stress affects the margin.

Investigation of Finite Element Analysis Variables by Elastic-Plastic Finite Element Analysis under Severe Seismic Loads

Hyun-Su Jang(장현수),Jong-Sung Kim(김종성) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11

In this study, the elastic-plastic finite element analysis was performed on the simulated model focusing on hot-leg surge nozzles in surge piping connecting pressurizer and hot-leg, which are nuclear safety class 1 component. In previous study, a elastic-plastic finite element analysis was performed on surge piping conncecting pressurizer and hot leg in APR-1400 under severe seismic loads, it is confirmed that seismic critical location occurred on the outer surface of the notch of the hot-leg surge nozzle. Therefore, in this study, before comparing dynamic characteristics with experiments, the finite element analysis variables (ex: accumulated plastic strain, equivalent plastic strain) were analyzed by performing elastic-plastic finite element analysis on model focused on hot-leg surge nozzle. It is assumed that the analysis target is made of the same material, SA312 TP316, which is one of the austenitic stainless steels. The analysis used the third-order combined nonlinear hardening model of the SA312 TP316 material and the seismic displacement time history corresponding to PGA 0.6g. As a result of the analysis, the maximum accumulated plastic strain occurred at the almost same location (outer surface of the notch of the hot-leg surge nozzle) as the previous study, and the strain at the strain gauge location in the subsequent experiments will be compared.

반무한체 표면아래의 소성변형을 고려한 3차원 탄소성 접촉해석에 대한 연구

문길환(Kilhwan Moon),이상돈(편집자),조용주(Yongjoo Cho) 한국트라이볼로지학회 2007 한국트라이볼로지학회 학술대회 Vol.2007 No.11

An elastic-plastic contact analysis is developed using a semi-analytical method. The elastic contact is solved within a Hertz theorem. The reciprocal theorem with initial strains is then introduced, to express the surface geometry as a function of contact stress and plastic strains. The irreversible nature of plasticity leads to an incremental formulation of the elastic-plastic contact problem, and an algorithm to solve this problem is set up. Closed form expression, which give residual stresses and surface displacements from plastic strains, are obtained by integration of the reciprocal theorem. The distribution of contact stress, residual stress and plastic strain are obtained by the changed surface geometry.

반무한체 표면아래의 소성변형을 고려한 3차원 탄소성 접촉해석

문길환(Kilhwan Moon),이상돈(Sangdon Lee),조용주(Yongjoo Cho) 한국트라이볼로지학회 2008 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.24 No.2

An elastic-plastic contact analysis is developed using a semi-analytical method. The elastic contact is solved within a Hertz theorem. The reciprocal theorem with initial strains is then introduced, to express the surface geometry as a function of contact stress and plastic strains. The irreversible nature of plasticity leads to an incremental formulation of the elastic-plastic contact problem, and an algorithm to solve this problem is set up. Closed form expression, which give residual stresses and surface displacements from plastic strains, are obtained by integration of the reciprocal theorem. The distribution of contact stress, residual stress and plastic strain are obtained by the changed surface geometry.

감육배관의 저주기 피로 평가를 위한 국부 탄소성 변형률 평가 방법

윤기봉(Kee Bong Yoon),마영화(Young Wha Ma),안중혁(Joong Hyok An),김윤재(Yun Jae Kim) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6

In order to assess the integrity of pipes with local thinning area, the plastic strain as well as the elastic strain at the root of thinned region are required particularly when fluctuating load is applied to the pipe. For estimating elastic-plastic strain at local wall thinning area in a straight pipe under tensile load, an estimation model with idealized fully circumferential constant depth wall thinning area is proposed. Based on the compatibility and equilibrium equations a nonlinear estimation equation, from which local elastic-plastic strain can be determined as a function of pipe/defect geometry, material and the applied strain was derived. Estimation results are compared with those from detailed elastic-plastic finite element analysis, which shows good agreements. Noting that practical wall thinning in nuclear piping has not only a circular shape but also a finite circumferential length, the proposed solution for the ideal geometry is extended based on two-dimensional and three-dimensional numerical analysis of pipes with circular wall thinning.

탄소성 변형률 기반 내진성능 평가 절차서 개발 방안

황종근,정일석,김범식,안상원,방혜진,이민희,정현섭 한국압력기기공학회 2018 한국압력기기공학회 논문집 Vol.14 No.2

A development plan for seismic capacity verification procedures of nuclear components based on the elastic-plastic strain (EPS) features is explained in this paper. The EPS methodology is more realistic to assess seismic responses of components to extreme seismic events beyond the safe shutdown earthquake (SSE) than current practices with the criteria of stress limits. The EPS based approach to analyze the seismic capacity of components can reduce over-conservatism in the current stress-based criteria and can incorporate the seismic responses of components deformed in plastic behavior by the motion of extreme earthquake.

스크래치가 존재하는 파열판의 소성변형률 기반 파열압력 평가

김만원(Maan-Won Kim),신인환(In-Hwan Shin),부명환(Myung-Hwan Boo) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12

The rupture disc is an important part for safely protecting the pressure vessel by bursting when the pressure vessel reaches a preset pressure. The failure pressure of the rupture disc can be predicted through engineering evaluation equation or numerical analysis such as finite element analysis at the design stage. The designed ruture pressure is verified by the test. However, a careful approach must be taken to apply existing evaluation methods to the disc which has scratches on its surface made during installation process because scratch makes a local stress concentration and disc material has usually a large deformation capability. In this study, the burst pressure was calculated by elastic plastic finite element analysis according to the position, shape, and depth of the scratch. The difference between the strength-based evaluation method and the plastic strain-based evaluation method was examined. It is appeared that the plastic strain-based evaluation method predicts more accurately the burst pressure of the rupture disc with scratches than the strength-based approach. The plastic strain-based finite element analysis results were compared with the burst test results and confirmed to be in good agreement.

변형률에 따른 배관 용접부 결함의 탄소성 파괴역학 해석

박지수(Ji-Su Park),김경민(Kyoung-Min Kim),장윤영(Youn-Young Jang),허남수(Nam-Su Huh) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.7

박막/쉘 혼합요소를 이용한 박판성형 해석과 박막/쉘 판별조건에 관한 연구

정동원(Dong-Won Jung),양경부(Kyoung-Boo Yang) 한국해양공학회 1998 韓國海洋工學會誌 Vol.12 No.2

This study is concerned with criterion for membrane to shell conversion in two-dimensional elastic-plastic finite element analysis using membrane/shell mixed element. It is well known that in the sheet metal forming some parts of the sheet deform under almost pure stretching (membrane) conditions, whereas other parts in contact with sharp tooling surfaces can develop significant bending strains. The membrane analysis has a short computational time; however, in the membrane analysis the bending effects can not be condidered at all. On the other hand, the shell analysis allows the consideration of bending effects, but involves too much computational time. So Onate1),2), Yang et al3),4) develped the membrane/shell mixed element. Onate introduced the energy ratio parameter and Yang et al introduced the ratio of thickness to radius of curvature as the criterion. In the present study we propose a new criterion by using the angle between both side elements in the nodal point.

압입인장물성을 반영한 지진취약설비 1등급 기기의 동적 탄소성 유한요소 지진해석 시 누적 소성 변형률을 고려한 균열거동 평가

장현수(Hyun-Su Jang),김준영(Jun-Young Kim),김종성(Jong-Sung Kim) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.7