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초음파 C-scan을 이용한 터빈 블레이드 열차폐코팅의 등온열화에 의한 박리 평가 기법
이호걸(Ho-Girl Lee),김학준(Hak-Joon Kim),송성진(Sung-Jin Song),석창성(Chang-Sung Seok) 한국비파괴검사학회 2016 한국비파괴검사학회지 Vol.36 No.5
가스터빈 블레이드는 고온 고압의 환경 아래 장시간 가동하기 위하여 초합금 모재에 세라믹 코팅으로 이루어진 열차폐코팅(thermal barrier coating, TBC)은 필수요소이다. 하지만 TBC 또한 가스터빈 가동 중 일정 열화온도 및 가동시간에서 top coat의 박리현상이 일어난다. TBC의 박리는 블레이드의 손상과 직결되므로 가스터빈의 안정적인 가동을 위해서 TBC의 박리 평가가 선행되어야 한다. 기존 비파괴평가 기법 연구는 산화알루미늄층(thermally grown oxide, TGO)의 생성 유무 또는 완전 박리의 정성적 평가가 이루어져 왔다. 본 연구에서는 TBC 박리를 정량적으로 평가하기 위해 초음파검사의 C-scan기법을 이용한 TBC의 부분박리손상 map을 구현하였다. 시편들은 1,100˚C로 등온열화하여 각각 열화시간을 변화시킨 시편들을 사용하였다. 단일 탐촉자를 이용한 펄스-에코법으로 C-scan을 수행하였고 TBC 내 부분박리를 검출하기 위해 초음파를 수침법으로 시편에 수직탐상하였다. 그리고 Rogers-Van Buren과 Kim의 이론 반사식을 이용하여 부분박리영역 지름이 1 mm부터 6 mm까지 부분박리지수를 도출했다. 이를 적용하여 각 부분박리지수에 따른 부분박리 손상 map을 영상화하였다. TBC는 열화시간이 증가할수록 부분박리지수에 관계없이 부분박리영역이 모두 증가함을 확인할 수 있었다. 또한 단일 시편 내에서 부분박리지수가 증가할수록 부분박리영역이 감소하는 것을 확인하였다. 부분박리손상 map의 부분박리영역에 따른 분포를 이용하여 TBC의 완전박리 기준과 잔여 수명을 또한 도출할 수 있었다. Thermal barrier coating (TBC) is an essential element consisting of a super-alloy base and ceramic coating designed to achieve long operational time under a high temperature and pressure environment. However, the top coat of TBC can be delaminated at certain temperatures with long operation time. As the delamination of TBC is directly related to the blade damage, the coupling status of the TBC should be assured for reliable operation. Conventional studies of nondestructive evaluation have been made for detecting generation of thermally grown oxide (TGO) or qualitatively evaluating delamination in TBC. In this study, the ultrasonic C-scan method was developed to obtain the damage map inside TBC by estimating the delamination in a quantitative way. All specimens were isothermally degraded at 1,100˚C with different time, having different partial delamination area. To detect partial delamination in TBC, the C-scan was performed by a single transducer using pulse-echo method with normal incidence. Partial delamination coefficients of 1 mm to 6 mm were derived by the proportion of the surface reflection signal and flaw signal which were theoretical signals using Rogers-Van Buren and Kim"s equations. Using the partial delamination coefficients, the partial delamination maps were obtained. Regardless of the partial delamination coefficient, partial delamination area was increased when degradation time was increased in TBC. In addition, a decrease in partial delamination area in each TBC specimen was observed when the partial delamination coefficient was increased. From the portion of the partial delamination maps, the criterion for delamination was derived.
High School Students' Perceived Creativity Self-efficacy and Emotions in a Service Learning Context
Ai-Girl Tan,Valerie Ho,Elizabeth Ho,Steve Ow 대한사고개발학회 2008 The International Journal of Creativity & Problem Vol.18 No.2
Our study examined the relationship of creativity self-efficacy and emotions of high school students (n = 279) in Singapore before and after they attended a three to five-day international service learning program. Participants completed a creativity self efficacy scale, the Positive Affect and Negative Affect Scale (PANAS), Satisfaction With Life Scale (SWLS) and Subjective Happiness Scale (SHS). We found a positive, significant correlation between creativity efficacy and positive affect, life satisfaction and subjective happiness but negative correlation with negative mood affect. In addition, students whose creativity efficacy was moderately high were found to have reported higher ratings of life satisfaction after having participated in service learning. Our findings provide initial evidence suggesting that service learning with positive intervention is positively related to creativity self-efficacy and happiness of youth.
A Study on the Optical Parts for a Semiconductor Laser Module
Jun-Girl Oh,이동길,Yang-Gyu Kim,이광훈,박영식,Kwang-Ho Jang,Seung-Goo Kang 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.10
A semiconductor laser module consists of a LD (laser diode) chip that generates a laser beam,two cylindrical lenses to collimate the laser beam, a high-reflection mirror to produce a large outputby collecting the laser beam, a collimator lens to guide the laser beam to an optical fiber and aprotection filter to block reflected laser light that might damage the LD chip. The cylindricallenses used in a semiconductor laser module are defined as FACs (fast axis collimators) and SACs(slow axis collimators) and are attached to the system module to control the shape of the laserbeam. The FAC lens and the SAC lens are made of a glass material to protect the lenses fromthermal deformation. In addition, they have aspheric shapes to improve optical performances. Thispaper presents a mold core grinding process for an asymmetrical aspheric lens and a GMP (glassmolding press), what can be used to make aspheric cylindrical lenses for use as FACs or SACs, anda protection filter made by using IAD (ion-beam-assisted deposition). Finally, we developed theaspheric cylindrical lenses and the protection filter for a 10-W semiconductor laser module.