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복합하중을 받는 평판에 존재하는 반타원 표면균열의 공학적 탄소성 파괴해석법
심도준,김윤재,최재붕,김영진,Shim, Do-Jun,Kim, Yun-Jae,Choi, Jae-Boong,Kim, Young-Jin 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.6
The present paper provides an engineering J estimation equation for surface cracked plates under combined bending and tension. The proposed equation is based on the reference stress approach, and the most relevant normalising loads to define the reference stress for accurate J estimations are given for surface cracked plates under combined bending and tension. Comparisons with J results from extensive 3-D FE analyses, covering a wide range of crack geometry, plate geometry and loading combination, show overall good agreement not only at the deepest point but also at arbitrary points along the crack front. for pure tension, agreement between the estimated J and the FE results is excellent, even at the surface point. On the other hand, for pure bending and combined bending and tension, the estimated J values become less accurate for locations close to the surface point. Thus the results in this paper will be useful to assess short-term fracture or low cycle fatigue of surface defects in plates under combined bending and tension.
구속효과를 구려한 가스배관 결함의 2차원적 파괴거동 해석에 관한 연구
심도준,장영균,최재붕,김영진,김철만,Sim, Do-Jun,Jang, Yeong-Gyun,Choe, Jae-Bung,Kim, Yeong-Jin,Kim, Cheol-Man 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.1
EFP(Fitness For Purpose) type defect assessment methodologies based on ECA(Engineering Critical Analysis) have been established and are in use for the structural integrity evaluation of gas pipelines. ECA usually includes the fracture mechanics analysis, and it is assumed that the J-integral uniquely characterizes the crack-tip stress-strain field. However, it has been proven that the J-integral alone can not be sufficient to characterize the crack-tip field under low levels of constraint with a single parameter. Since pipeline structures are made of ductile material, locally loaded in tension, cracks may experience low level of constraint, and therefore, J-dominance will be lost. For this reason, the level of constraint must be quantified to establish a precise assessment procedure for pipeline defects. The objective of this paper is to investigate the fracture behavior of a crack in gas pipeline(KS D 3507) by quantifying the level of constraint. For this purpose, tensile tests and CTOD tests were performed at room temperature(24$\^{C}$) and low temperature(-40$\^{C}$) to obtain the material properties. J-Q analyses were performed for SENB and SENT specimens based on 2-D finite element analyses, in order to investigate the in-plane constraint effects on pipeline defects. For precise assessment of cracks, especially shallow cracks, in KS D 3507 pipeline, constraint effect must be considered.
인장하중이 작용하는 평판에 존재하는 반타원 표면균열의 J-적분 계산식
심도준,김윤재,최재붕,김영진,Sim, Do-Jun,Kim, Yun-Jae,Choe, Jae-Bung,Kim, Yeong-Jin 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.11
This paper provides d simplified engineering J estimation method fur semi-e1liptical surface cracked plates in tension, based on the reference stress approach. Note that the essential element of the reference stress approach is the plastic limit lead in the definition of the reference stress. However, for surface cracks, the definition of the limit load is ambiguous ("local" or "global"limit lead), and thus the most relevant limit load (and thus reference stress) for the J estimation should be determined. In the present work, such limit load solution is found by comparing reference stress bated J results with those from extensive 3-D finite element analyses. Validation of the proposed equation against FF J results based on tactual experimental tensile data of a 304 stainless steel shows excellent agreements not only far the J values at the deepest point but also for those at an arbitrary paint along the crack front, including at the surface point. Thus the present results provide a good engineering tool for elastic-plastic fracture analyses of surface cracked plates in tension.
감육형상 및 내압이 원자력 감육배관의 파단에 미치는 영향 -내압과 굽힘모멘트가 동시에 작용하는 경우-
심도준,임환,최재붕,김영진,김진원,박치용,Shim, Do-Jun,Lim, Hwan,Choi, Jae-Boong,Kim, Young-Jin,Kim, Jin-Won,Park, Chi-Yong 대한기계학회 2003 大韓機械學會論文集A Vol.27 No.5
Failure of a pipeline due to local wall thinning is getting more attention in the nuclear power plant industry. Although guidelines such as ANSI/ASME B31G and ASME Code Case N597 are still useful fer assessing the integrity of a wall thinned pipeline, there are some limitations in these guidelines. For instance, these guidelines consider only pressure loading and thus neglect bending loading. However, most Pipelines in nuclear power plants are subjected to internal pressure and bending moment due to dead-weight loads and seismic loads. Therefore, an assessment procedure for locally wall thinned pipeline subjected to combined loading is needed. In this paper, three-dimensional finite element(FE) analyses were performed to simulate full-scale pipe tests conducted for various shapes of wall thinned area under internal pressure and bending moment. Maximum moments based on true ultimate stress(${\alpha}$$\sub$u,t/) were obtained from FE results to predict the failure of the pipe. These results were compared with test results, which showed good agreement. Additional finite element analyses were performed to investigate the effect of key parameters, such as wall thinned depth, wall thinned angle and wall thinned length, on maximum moment. Also, the effect of internal pressure on maximum moment was investigated. Change of internal pressure did not show significant effect on the maximum moment.