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큰 진폭의 반복하중 조건에서 저합금강과 스테인리스강의 손상거동에 미치는 노치 영향
김상언(Sang Eon Kim),김진원(Jin Weon Kim),김종성(Jong Sung Kim) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
System, structure, and components (SSCs) of nuclear power plants (NPPs) are subjected to large amplitude load- and displacement- controlled cyclic loads under beyond design basis earthquake (BDBE). Typically, high stressed and strained areas are susceptible to damage under cyclic loading condition, and the effect of stress and strain concentrations on the failure behaviors of materials are well known under low amplitude cyclic loading condition. However, the effect is still unclear under large amplitude cyclic loads that generate large cyclic plastic deformation. In this case, the failure mode and pattern are influenced by the loading type and stress state. Thus, this study conducted failure tests using notched-bar type specimen with two different notch radii under large amplitude strain- and load-controlled cyclic loads. SA508 Gr.1a low-alloy steel (LAS) and SA312 TP316 stainless steel (SS), which are materials commonly used as structural materials in NPPs, were used in the test. All tests were conducted at room temperature (RT) under a quasi-static rate. From the result of tests, the effect of notch on the load-displacement behaviors, failure cycles, and failure mode were investigated for each cyclic loading type.
방향과 위치에 따른 배관 엘보우의 기계적 물성 불균일성 평가
김상언(Sang Eon Kim),김진원(Jin Weon Kim),이대영(Dae Yong Lee),박흥배(Heung Bae Park) 대한기계학회 2021 大韓機械學會論文集A Vol.45 No.2
배관 엘보우에서 기계적 물성의 불균일성을 파악하기 위해서, SA403 WP316 스테인리스강(SS)과 SA234 WPB 탄소강(CS) 엘보우를 대상으로 시편 방향과 원주방향 위치에 따른 인장시험을 상온과 운전온도에서 수행하였다. 시험 결과, 시험온도와 엘보우 종류에 관계없이 방향에 따른 기계적 물성 차이는 크지 않지만, 엘보우에서 원주방향 위치에 따른 기계적 물성 차이는 뚜렷하였다. SA403 WP316 SS 엘보우는 곡관부 측면에서 최대 항복강도와 최소 연신율을 보였으며, 외륜에서 최소 항복강도와 최대 연신율을 보였다. SA234 WPB CS 엘보우는 측면과 외륜에 비해 내륜에서 뚜렷이 높은 항복강도와 낮은 연신율을 보였으며, SA403 WP316 SS 엘보우에 비해 원주방향 위치에 따른 기계적 물성의 편차가 컸다. 원주방향 위치에 따른 기계적 물성의 차이는 각 엘보우의 제작 공정에 따른 미세조직 차이에 기인하는 것으로 확인되었다. To investigate the nonuniformities in the mechanical properties in pipe elbows, tensile tests were conducted using specimens machined from different orientations and locations of SA403 WP316 stainless steel (SS) and SA234 WPB carbon steel (CS) elbows. Regardless of the test temperature and elbow type, the mechanical properties were nearly independent of specimen orientations but highly dependent on the circumferential locations. In the SA403 WP316 SS elbows, the highest yield strength and lowest elongation were observed at the crown, and the minimum yield strength and maximum elongation were observed at extrados. In the SA234 WPB CS elbows, the intrados showed the highest yield strength and lowest elongation, while the properties at the crown and extrados were almost similar. The difference in mechanical properties along the circumferential locations was more pronounced in the SA234 WPB CS elbows than SA403 WP316 SS elbows. Moreover, these differences are associated with local differences in the microstructures of elbows, which depend on their manufacturing processes.