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Al6061-T6 평판 시편의 노치반경과 두께가 파괴 메커니즘에 미치는 영향
두샤오(Xiao Du),왕량(Liang Wang),최낙삼(Nak-Sam Choi) 대한기계학회 2021 大韓機械學會論文集A Vol.45 No.3
Al6061-T6 합금의 연성파괴는 네킹의 발생 시에 생기는 삼축인장응력과 관계가 있다. 노치 반경과 두께에 따른 시편 표피와 내부의 응력상태가 달라진다. 본 연구에서는 두께 4 mm, 8 mm의 평판으로 노치 없는 시편(un-notched), 노치 반경이 큰 시편(L-notched, R228.1 mm), 노치 반경이 작은 시편(S-notched, R2.5 mm)을 제작하였다. 슬립라인 이론(slip line theory), 타원기준(ellipse criterion), 유한요소법(FEM), 2D 디지털 이미지 상관법(2D-DIC)을 이용하여 노치 반경과 두께에 따른 응력상태와 파괴위치를 해석하였으며 주사 전자현미경(SEM) 관찰을 병행하여 파괴 양상을 관찰하였다. 노치반경이 작을수록 응력집중으로 인해 시편 내부에 형성한 높은 삼축인장응력이 파괴를 주도하였다. 두께가 커지면 파괴는 삼축인장응력과 최대전단응력에 의한 혼합모드의 파괴거동을 보였다. The fracture behavior of Al6061-T6 alloy is related to stress triaxiality formation during the local necking process of the specimen. Distribution of triaxial tensile stress varies with different notch radii and specimen thickness. In this study, plate specimens (un-notched), specimens with large notch radius (L-notched, R228.1 mm), and specimens with small notch radius (S-notched, R2.5 mm) were made of aluminum alloy plates (thickness 4 mm, 8 mm). Slip line theory, the ellipse criterion, finite element method (FEM), and 2D digital image correlation (2D-DIC) were used to find the effect of notch radii and specimen thickness on stress state distributions and initial fracture mechanisms. A scanning electron microscope (SEM) was used to observe the initial fracture surface. For a small notch radius causing high stress concentration, the fracture began at a site close to the notch tip due to high triaxial tensile stress. With increasing specimen thickness, the fracture surface showed a mixed mode failure behavior caused by both the triaxial tensile stress and maximum shear stress.
삼축 응력이 인가된 Alloy 600의 일차수 응력부식균열 거동에 대한 연구
유승창(Seung Chang Yoo),최경준(Kyoung Joon Choi),김지수(Ji-Soo Kim),최병호(Byoung Ho Choi),김윤재(Yun-jae Kim),김종성(Jong Sung Kim),김지현(Ji Hyun Kim) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
In this study, the effects of triaxial stress was investigated in terms of primary water stress corrosion susceptibility. Thermally aged Alloy 600 specimens were prepared via accelerated heat treatment at 400 °C which is one of the highest temperature which will not cause the formation of excessive carbides or precipitates which will not be formed at nuclear power plant primary circuit environment. Triaxial stress was then applied by making round notch at the surface of round tensile specimen. The crack initiation time ere measured in-situ by direct current potential drop method during slow strain rate test at primary water condition. At the notched specimen, cracks were mainly observed at the region where shear stress is focused. Also the stair shape of fracture surface was observed, which might cause by enhanced localized plasticity and multiple number of activated slip system under triaxial stress state.
Alloy 600의 PWSCC에 미치는 열적 시효 및 삼축 응력의 영향
유승창(Seung Chang Yoo),김종성(Jong Sung Kim),황일순(Il Soon Hwang),김지현(Ji Hyun Kim) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11
In this study, the effects of triaxial stress was investigated in terms of primary water stress corrosion susceptibility. Thermally aged Alloy 600 specimens were prepared via accelerated heat treatment at 400 ℃ which is one of the highest temperature which will not cause the formation of excessive carbides or precipitates which will not be formed at nuclear power plant primary circuit environment. Triaxial stress was then applied by making round notch at the surface of round tensile specimen. The crack initiation time ere measured in-situ by direct current potential drop method during slow strain rate test at primary water condition. At the notched specimen, cracks were mainly observed at the region where shear stress is focused. Also, the stair shape of fracture surface was observed, which might cause by enhanced localized plasticity and multiple number of activated slip system under triaxial stress state.