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문재흠,김석일,이형대 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.
Air-oil lubrication has been widely used for high-speed spindle bearings because its oil delivery is positive and can be controlled very accurately. In this study, the effects of air-oil lubrication conditions, such as the oil discharge quantity, oil discharge interval, oil viscosity, air supply rate and tube length, were analyzed with respect to the variation of the oil supply rate. The analysis was carried out by using an air-oil lubrication characteristics evaluation system which was consisted of an air-oil lubrication unit, oil absorbent paper feeding unit and image processing unit. The variation of the oil supply rate discharged from the air-oil lubrication unit was gauged as the variation ratio of the oil band width on the oil absorbent paper measured by the image processing unit. A prediction model for the variation ratio of the oil band width was established based on a response surface method, and its reliability was proved by the fact that the predicted variation ratios of the oil band width agreed well with the measured variation ratios under the various air-oil lubrication conditions. In particular, the relationships between the variation of the oil band width and the air-oil lubrication conditions were examined by analyzing the interactions between the experimental factors.
문재흠 한국구조물진단유지관리공학회 2010 한국구조물진단유지관리공학회 논문집 Vol.14 No.4
최근들어 구조물공사에 적용되는 콘크리트가 고강도화 되어가는 추세로서 크리프와 같은 콘크리트의 역학적 거동에 대한 기존 설계 예측식에 대한 전면적인 검토가 필요한 시점이다. 이에, 본 연구에서는 현행 국내 철근콘크리트 구조설계기준상의 크리프계수 예측 모델식에 대한 강도대별 적용 타당성을 검토하기 위한 일환으로 기존의 제안 모델식인 ACI 209R, CEB-FIP MC90 및 EC2 모델식을 검토 하였으며, 실험결과와 비교검토를 수행하였다. 모델식 검토결과, CEB-FIP MC90 모델의 개선식인 EC2 모델이 고강도대의 콘크리트에 대한 크리프계수를 보다 현실적으로 예측함을 확인할 수 있었으며, 실험결과와도 상대적으로 좋은 상관성을 보임을 확인하였다. Recent concrete structures have been being constructed with higher strength concrete than normal strength concrete. Therefore, it is necessary to review the applicabilities of current design codes and models for the prediction of mechanical behaviors of concrete materials such as creep. To investigate the applicability of creep model with the consideration of the strength level of concrete, three current models (ACI 209R, CEB-FIP MC90 and EC2) were studied and compared with series of experimental results. It was shown that EC2 model which is the updated model of CEB-FIP MC90 better predicts creep coefficient for high strength level concretes and showed relatively good agreements with experimental data.
고속 비상체 충돌에 대한 고성능 섬유보강 시멘트 복합체의 방호성능 평가
문재흠(Moon, Jae-Heum),박정준(Park, Jung-Jun),박기준(Park, Gi-Joon),조현우(Jo, Hyun-Woo),김성욱(Kim, Sung-Wook),이장화(Lee, Jang-Hwa) 한국산학기술학회 2015 한국산학기술학회논문지 Vol.16 No.7
공공시설물의 대형화 및 도심지로의 인구 밀집화에 따라 충돌 또는 폭발과 같은 하중조건 하에서의 구조물 방호성능 의 중요성이 대두되고 있다. 그러나, 구조물의 방호설계 및 시공에 있어서 필수적이라 할 수 있는 구조재료 또는 자재에 대한 기술개발은 제대로 이루어지고 있지 않은 실정이다. 이에, 본 연구에서는 고성능 섬유보강 시멘트 복합재로의 기본적인 방호 성능 및 방호용 자재로서의 적용 가능성을 파악하고자 40 mm 가스건을 사용한 충격 파괴시험을 수행하였다. 실험 수행 결과, 고성능 섬유보강 시멘트 복합재료에 있어서 시멘트 매트릭스의 강도 및 보강섬유가 방호성능 향상에 도움이 됨을 확인할 수 있었다. The importance of public infrastructures’ protection against crash or blast loads has been emerging issue as structures are becoming bigger and population densities in downtown cities are growing up. However, there exists no sufficient study which considers the developments of protective building materials, that are essential for protective design and construction. To assess the protection performance and the applicability as protective materials of high performance fiber reinforced cementitious composites(HPFRCC), this study performed the impact tests with 40 mm gas-gun propelled projectile crash machine. From this study, it has observed that both high compressive strength of cement matrix and fiber reinforcement are beneficial for the improvement of impact resistance.