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열 및 기계적 반복하중 하의 내열금속 표면 홀 주변 산화막의 변형 및 응력해석
이봉훈(Feng-Xun Li),강기주(Ki-Ju Kang) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.9
가스터빈엔진 내의 블레이드에서는 표면에 외부의 찬 공기를 흘려주는 작은 냉각 홀들을 가공하고 열 차단 코팅시스템을 코팅하는 방법으로 기지금속을 고온에서 보호한다. 열 차단 코팅은 열 피로 과정에서 산화막의 성장 및 접합층과 산화막의 열팽창계수의 불일치로 산화막내부에 잔류응력이 발생하며 궁극적으로 코팅층의 분리를 유발한다. 본 연구에서는 내열합금 시편 표면에 작은 홀을 가공하여 여러 가지 고온 유지 조건에서 열 및 기계적 피로 시험을 수행하여 홀 주위의 산화막의 변형을 관찰하였다. 실험결과 기계적 피로가 홀 주위의 산화막의 변형에 중요한 영향을 미치며, 동일한 산화막 두께에서 고온 유지 시간이 짧을수록 변형이 쉽게 발생 하였다. 또한 본 연구에서는 홀 주위 산화막의 응력해석을 위한 이론적인 연구도 시도되었다. In the hot section of a gas turbine, the turbine blades were protected from high temperature by providing a thermal barrier coating (TBC) as well as by cooling air flowing through internal passages within the blades. The cooling air then passed through discrete holes on the blade surface, creating a film of cooling air that further protects the surface from the hot mainstream flow. The holes are subjected to stresses resulting from the lateral growth of thermally grown oxide, the thermal expansion misfit between the constituent layers, and the centrifugal force due to high-speed revolution; these stresses often result in cracking. In this study, the deformation and cracks occurring near a hole on a heat-resistant alloy subjected to thermo-mechanical cycling were investigated. The experiment showed that cracks formed around the hole depending on the applied stress level and the number of cycles. These results could be explained by our analytic solution.
기계적 및 열적 피로가 교정용 접착제의 결합강도에 미치는 영향
신완철,김종성,김정기 대한치과교정학회 1996 대한치과교정학회지 Vol.26 No.2
본 연구의 목적은 기계적 및 열적피로가 전단결합강도에 미치는 영향을 알아보기위한 것이다. 3종의 비반죽형 접착제(Ortho-one, MonoLokMonoLok¹System 1+ )로 mesh형의 금속 브라켓(ormesh)을 교정목적으로 발거된 소구치의 법량질면을 평탄하게 한 후 부착하고 100만회의 반복비틀림과 1,000회의 thermocycling을 가하였다. 그 후 Instron을 이용하여 전단결합강도를 측정하여 다음과 같은 결과를 얻었다. 1. 접착제의 Knoop 경도치는 thermocycling 전에는 Monolok² 가 64.03㎏/㎟ 으로 가장 크고, System 1?? 가 31.60㎏/㎟으로 가장 작았으며, thermocycling 후에도 Monolok²가 38.08㎏/㎟로 가장 크고 System 1??가 20.87㎏/㎟로 가장 작았다. thermocycling 전후 비교시 Ortho-one, Monolok2, System 1 모두에서 유의한 감소를 보였다.(P<0.01). 2. 정적 시험군의 전단결합강도는 세군간에 유의한 차를 보이지 않았다(P>0.01). 3. 1,000회의 thermocycling 후의 전단결합강도는 Monolok??군이 19.43MPa로 가장 크고 Ortho-one 군이 13.66MPa로 가장 작게 나타났으며, thermocycling 전과 비교시 Ortho-one 군(P<0.01), System 1??군(P<0.05)에서 유의한 감소를 보였다. 4. 100만회의 반복 비틀림을 가한 후의 전단결합강도는 세군에서 유사하였으며, 피로시험전과 비교시 세군 모두 유의한 감소를 보이지 않았다.(p>0.01). 5. 접착계면의 파절양상은 모든 군에서 실험조건에 관계없이 주로 브라켓/레진 계면에서 나타났다. The purpose of this study was to examine the effects of mechanical and thermal fatigue onthe shear bond strength(SBS) of stainless steel mesh brackets bonded to human premolar teeth with 3 no-mix adhesives. The stainless steel mesh bracket was Ormesh(Ormco, .022 slot) and three types of no-mix adhesives were Ortho-one(Bisco), Monolok(RMO), System 1(Ormco), The 10 loadcycles of |7.4x10sin2 ft|g·㎝ and the 1,000 thermocycles of 15 second dwell time in each bath of 5C and 55C were acturated as mechanical and thermal fatigue stress, and SBS were measured after each fatigue test. The fracture sites were analyzed by steroscope and scanning electron microscope. The results obtained were summarized as follows; 1. Before thermocycles, Monolok showed the highest Knoop hardness number(KHN, 64.03㎏/㎟) and System 1 showed the lowest value(31.60㎏/㎟). After themocycling, Monolok also showed the highest KHN(38.03㎏/㎟) and system 1 showed the minimum(20.87㎏/㎟). The KHNof Ortho-one, Monolok, System 1 significantly decreased after thermocycling(P<0.01). 2. In static shear bond test, three adhesives had no significant differences in the SBS(P>0.01). 3. After themocycling test, Monolok showed the maximum SBS(19.34±2.23MPa). The SBS of Ortho-one(P<0.01) and System 1(P<0.05) significantly decreased after 10 thermocycles. 4. The SBS of three adhesives after 10 loadcycles were similar and were not significantly decreased compared with static group(P>0.01). 5. The failure sites were usually bracket/resin interface in all groups irrespective of experimental conditions.
열 및 기계적 반복하중 하의 내열금속 표면 홀 주변 산화막의 변형 및 응력해석
이봉훈(Feng-Xun Li),강기주(Ki-Ju Kang) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.4
In a hot section of gas turbine, the turbine blades were protected from high temperature by not only a thermal barrier coating (TBC) but also cooling air fed through internal passages within the blade. The cooling air is then passed through discrete holes in the blade surface, creating a film of cooling air, further protects the surface from the hot mainstream flow. The holes are subjected to stresses due to the lateral growth of the thermally-grown oxide, the thermal expansion misfit between the constituent layers and centrifugal force by high speed revolution, which often results in cracking. In this work, the deformation and cracks occurring near a hole on a heat-resistant alloy subject to thermo-mechanical cycling were investigated. The experiments showed that during thermo-mechanical cycling the cracks occur around the hole depending applied stress level and number of cycles, which could be explained by analytic solution.
오스테나이트계 스테인리스 SUS 304H 강의 열기계적 피로 특성
양호영(Ho-Young Yang),김재훈(Jae-Hoon Kim) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
In power plants, austenite stainless steel are using as a superheater tube, reheater tube, boiler pipe, since they have a good corrosion resistance, mechanical property and oxidation resistance at high temperature. In this paper, a TMF(Thermal mechanical fatigue) test were carried out to observe thermal fatigue behavior and microstructure of 304H stainless steel which is mainly using a high temperature system of HRSG(heat recovery steam generator). The substructural changes of the starting microstructure were also found to be responsible for the reductino of the fatigue life. The tests specimens of TMF are observed by Scanning Electron Microscopy (SEM) to analyze material behaviro of SUS 304H.
열 및 기계적 피로하중에 대한 Fecralloy 표면 홈의 변형저항성 평가
이봉훈(Feng-Xun Li),강기주(Ki-Ju Kang) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Durability of structural components operating at high temperature depends on the resistance of deformation of bond coat. In this work, the thermal-mechanical fatigue tests were performed under various thermal and mechanical loads with Fecralloy specimens with and without yttrium dopant and the deformation of surface grooves was observed. The effects of the level of temperature and load, and groove orientation as well as the effect of the ratio of curvature on the deformation of the grooves were investigated, the results show that groove deformation depends heavily on the load orientation, and that the higher level of temperature and load induces the larger deformation near the grooves. However, the addition of yttrium dopant was found to suppress the deformation near groove.
열 및 열-기계적 피로에 의한 내열합금 표면의 홈의 형상변화
이봉훈(Feng-Xun Li),선신규(Shin-Kyu Sun),강기주(Ki-Ju Kang) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
The existence of grooves on the surface of bond coat has significant effect on the instability of thermal barrier system. In this work, the thermal-mechanical fatigue experiments were performed under various thermal and mechanical loads for FeCralloy specimens with and without yttrium dopant to observe the deformation of surface grooves. The effect of temperature, fatigue load and the ratio of curvature on the deformation of grooves were investigated. As the results, it has been found that the higher load level and the higher curvature ratio induces the larger deformation near the grooves. However, the addition of yittrium dopant induces the adverse results.