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구재민(Jae-Mean Koo),석창성(Chang-Sung Seok),강민성(Min-Sung Kang),김대진(Dae-Jin Kim),이동훈(Dong-Hoon Lee),김문영(Mun-Young Kim) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.4
가스터빈 블레이드는 터빈 가동 시 발생하는 고온화염으로부터 블레이드를 보호하고, 구조물의 표면 온도를 안전한 수준으로 낮추기 위하여 블레이드 표면에 열차폐 코팅(TBC; Thermal barrier coating)을 하여 사용하고 있다. 본 논문에서는 가스터빈 1단 블레이드에 적용되는 코팅 방식을 이용하여 코인형 시험편을 제작하였고 열화 온도 및 유지 시간의 변화에 따른 코팅 계면 산화물의 성장 거동을 분석하였다. 코팅 단면에 대하여 코팅 계면 산화물의 두께와 마이크로 비커스 경도를 측정하여 열화 특성을 평가 하였다. 또한 성분분석을 통하여 미세조직의 변화를 관찰함으로써 열차폐 코팅의 열적 열화특성을 평가하였다. The thermal barrier coating of a gas turbine blade was degraded by isothermal heating in a furnace and by varying the exposure time and temperature. Then, a micro-Vickers hardness test was conducted on the cross section of the bond coat and Ni-based superalloy substrate. Further, the thickness of TGO(Thermally Grown Oxide) was measured by using an image analyzer, and the changes in the microstructure and element contents in the coating were analyzed by using an optical microscope and by performing SEM-EDX analysis. No significant change was observed in the Vickers hardness of the bond coat when the coated specimen was degraded at a high temperature; delamination was observed between the top coat and the bond coat when the coating was degraded for 50 h at a temperature 1,151℃.
잔류응력으로 인한 응력비 변화를 고려한 U자형 구조의 피로특성 평가
김상영(Sang Young Kim),구재민(Jae Mean Koo),석창성(Chang Sung Seok),모진용(Jin Yong Mo) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
Mechanical structures with power sources experience repeated force produced by motors. As a result, the life of the pipes reduces and ultimately, the pipes collapse. In most cases, the U-shape pipe is made from a straight pipe by complicated bending work. During this work process, plastic deformation of the pipe produces residual stress in the pipe. This residual stress significantly affects the fracture behavior of the pipe and induces the change of the stress ratio (min. stress/Max. stress = R). For this reason, residual stress has to be evaluated. In this paper, the residual stress of a U-shaped pipe was evaluated by FEM analysis. In addition, fatigue tests of the U-shaped pipe were performed by using a uniaxial fatigue testing machine. The results of the fatigue test were modified with the results of FEM (Finite Element Method) analysis for residual stress. The modified fatigue test results of the U-shaped pipe were compared with those of a straight pipe.
수정된 하중비법을 이용한 배관 시험편의 균열 길이 계산
최정훈(Jung-Hun Choi),구재민(Jae-Mean Koo),석창성(Chang-Sung Seok),허용(Yong Huh),박재실(Jae-Sil Park) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.12
The objective of this paper is to apply the load ratio method to the measurement of the crack length of the real scale pipe specimen. The load ratio method was modified and finite element analyses were performed to derive the relationship between the normalized compliance and the normalized crack length for the pipe specimen. In order to measure the crack length, the direct current potential drop method and the modified load ratio method were applied to the pipe test. The applicability of the modified load ratio method was confirmed by comparing the calculated crack length with the measured crack length from the pipe experiment.
협계용접부 강도 불균일을 고려한 소성 η계수 평가 (I)
허용,김형익,선광상,구재민,석창성,Huh, Yong,Kim, Hyung-Ick,Seon, Kwang-Sang,Koo, Jae-Mean,Seok, Chang-Sung 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.6
This study evaluated the influence of the strength mismatch of HAZ for a plastic ${\eta}$-factor, which is the principle parameter determining the plastic portion of J-integral to assess the fracture toughness of the weldment. The specimen of tensile and hardness test was manufactured from the piping applying narrow-gap welding, and the mechanical properties of weldment, HAZ and a base metal were obtained. To perform the finite element analysis according to the ratio of strength mismatch, the material properties was chosen with the change of strength using the determination method of Ramberg-Osgood constant. Also, the influence of the strength mismatch of HAZ was determined using finite element analysis by those properties.