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Thermally Grown Oxide의 고온 크리프에 따른 열차폐 코팅의 잔류응력 분포에 관한 유한요소해석
장중철,최성철,Jang, Jung-Chel,Choi, Sung-Churl 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.8
The residual stress changes on thermo-mechanical loading in the interface region of the Thermal Barrier Coating (TBC)/Thermally Grown Oxide (TGO)/Bond Coat (BC) were calculated on the TBC-coated superalloys using a Finite Element Method (FEM). It was found that the residual stress of the interface boundary was dependent upon mainly the oxide formation and the swelling rate of the oxide by creep relaxation. During an oxide swelling, the relaxation of residual stress which is due to creep deformation increased the TBC's life. In the case of the fine grain size of TGO scale, the TBC stresses piled up by oxide swelling could be relaxed by diffusional creep effect of TGO.
에멀젼 건조법에 의한 Bi-2223 초전도 분말과 테이프 제조
장중철,이응상,이희균,홍계원 한국세라믹학회 1997 한국세라믹학회지 Vol.34 No.2
액상 분말 합성법 중의 하나인 에멀젼 건조 방법에 의한 분말 합성은 조성 조절이 용이하고 균질한 미립자 분말을 제조할 수 있는 장점을 지니고 있다. 에멀젼 건조법을 사용하여 합성 분체의 초기 형상과 입도를 제어하고 근본적으로 더욱 개선된 homogeneity를 얻었다. 에멀젼의 분리를 억제시킬 수 있는 계면활성제, 오일상 및 수용액의 혼합비를 조절함으로써 Bi(Pb)-Sr-Ca-Cu-O 초전도 분말을 제조할 수 있었다. 이 방법에 의하여 합성된 산화물 초전도체 분말의 특성 및 pellet으로 성형한 시편을 열처리하여 미세구조와 전기적 특성을 조사하였다. 또한, OPIT(Oxide Powder-in-tube)법에 의해 테이프를 제작하여 미세구조와 전기적 특성을 관찰하였다. 합성된 분말의 입자크기는 1$\mu$m이하의 구형이었으나 대부분이 2~5$\mu$m크기로 응집되어 있었다. Ar분위기의 1/13atm 산소분압(Po2)에서 84$0^{\circ}C$로 72시간 동안 열처리한 덩어리형 시편의 임계저항온도는 108K이었으며, 1차와 2차 열처리한 테이프의 임계전류는 각각 0.4A와 1.5A이었다. The powder preparation by using emulsion drying method, one of the chemical powder fabrication methods has the advantages; easy to control the chemical stoichiometry and to fabricate homogeneously fine particles. In the present study, the initial morphology and size distribution of the powder fabricated by using emulsion dry-ing method were controlled and were improved the homogeneity. By carefully controlling the mixing ratio of oil phase and aqueous solution and surfactant of preventing emulsion separation, the Bi(Pb)-Sr-Ca-Cu-O su-perconducting powders were prepared. The properties of the superconducting powder fabricated by this method and the microstructures and superconducting properties of the pelletized samples were investigated. The microstructures and electric properties of the tapes prepared by oxide powder-in-tube method were in-vestigated. The fabricated powder was spherical with less than 1$\mu$m but most of them was agglomerated with 2~5$\mu$m in size. The critical temperature of the pelletized sample annealed at 84$0^{\circ}C$ for 72 hours in oxygen par-tial pressure of 1/13atm in Ar atmosphere was 108K. And the critical current of the first and second annealed tapes in air prepared by oxide powder-in-tube process were 0.4A and 1.5A, respectively.
열차폐 코팅의 TGO 성장과 형상비에 따른 TC-BC-TGO 계면에서의 잔류응력 변화에 대한 유한요소해석
장중철,최성철,Jang, Jung-Chel,Choi, Sung-Churl 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.7
The residual stresses in the interface region of the Thermal Barrier Coating (TBC)/Thermally Grown Oxide (TGO)/Bond Coat (BC) were calculated on the TBC-coated superalloy samples using a Finite Element Method (FEM). It was found that the stress distribution of the interface boundary was dependent upon mainly the geometrical shape or its aspect ratio and the thickness of TGO layer, which was formed by growth and swelling behavior of oxide layer. Maximum compressive residual stress in the TBC/TGO interface is higher than that of the TGO/bond coat interface, and the tensile stress had nothing to do with change of an aspect ratio. The compressive residual stresses in the TBC/TGO and TGO/bond coat interface region increased gradually with the TGO growth.
장중철(Jung-Chel Chang),장성용(Sung-Young Chang),김범수(Beom-Soo Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
The Blade is typical hot gas part of gas turbine. especially 1st blade is operated severe environments which include both above 1300℃ high temperature gas and thermal stress by high speed rotation of 3600 rpm. To obtain high efficiency, thermal barrier coating(TBC) and internal cooling system have been used. In this study, we examined thermal barrier coating and base materials of 1st and 2nd blades to evaluate degree of degradation, and then investigate the type and cause of failure by degradation.
장중호,최현철 한국통신학회 1999 韓國通信學會論文誌 Vol.24 No.6
12GHz-13GHz에서 동작하는 두 개의 선형 직교 편파된 신호를 분리전송하기 위한 협대역 직교모드편파분리기를 설계 및 제작하였다. 제안된 구조는 도파관 형태의 main arm과 side arm으로 구성되어 있다. 각 모드에 대한 전송손실 및 격리도 특성을 향상시키기 위하여 계단형 도파관 트랜스포머를 설계하고 인덕티브 포스트를 삽입하였다. 설계 제작한 직교모드편파분리기의 측정결과 각 모드에 대한 전송손실은 1dB이내, 각 포트의 격리도는 20dB이상을 보였다. This paper presents a narrow-band orthomode transducer(OMT) based on waveguide to waveguide transitions which can separate two linearly polarized orthogonal modes. This operates in the range 120Hz-13GHz frequency band. It consists of two parts, main arm and side arm. Stepped transformers are designed and an inductive post is inserted to improve the characteristics of the transmission loss and isolation. This paper also presents results from fabricated OMT These results show that the transmission loss is less than 1dB and the isolation between the ports for the OMT is above 20dB.