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고체윤활 Graphite 소재의 마모 특성에 관한 연구
양호영(Hoyoung Yang),김재훈(Jaehoon Kim),김연욱(Yeonwook Kim),하재석(Jaeseok Ha),박성한(Sunghan Park),이환규(Hwankyu Lee) 한국추진공학회 2013 한국추진공학회지 Vol.17 No.5
The important design factors for designing solid lubricating of dynamic seal are tightness, wear resistance and lubricant films. In this study, the effect factors influenced solid lubricating roperties of the graphite were analyzed and wear behaviour caused for various test conditions was compared with results obtained from reciprocating wear tests. Also the optimal conditions for formation of lubricant films were investigate to evaluate wear properties of graphite materials. The repeated procedure for the formation of wear particles and lubricant films, and the dissipation of lubricant films was estimated the wear mechanisms with changes of wear depth. Therefore the lubricant film of graphite seal was generated by adhesion of wear particles on the worn surface and it was very useful in wear characteristics.
고속압력하중부가에 의한 고체추진제의 균열진전평가에 관한 연구
하재석(Jaeseok Ha),김재훈(Jaehoon Kim),양호영(Hoyoung Yang) 한국추진공학회 2012 한국추진공학회 학술대회논문집 Vol.2012 No.5
창이 있고 밀폐되어있는 시험챔버를 사용하여 고속압력하중부가에 의한 고체추진제의 균열진전시험을 수행하였다. 고체추진제 예균열 시험편은 시험챔버내에 설치되고, 고속압력하중을 부가하기 위해 어큐뮬레이터 내에 고압으로 축적된 질소가스를 가압밸브를 통해 시험챔버 내에 가압하였으며, 시험챔버내의 압력이 설정압력에 도달하게 되면 가압밸브는 닫히고 배기밸브를 통해 시험챔버는 감압이된다. 시험결과로부터 시간에 따른 시험챔버압력을 나타내는 압력-시간 선도를 얻었으며, 선도로부터 가압비(ΔP/Δt)를 계산하였다. 3가지 가압비 64.34, 73.86, 85.44 ㎫/s 에 대한 시험을 수행하였으며, 가압비에 따른 균열진전길이가 측정되었다. 또한 고속 디지털카메라촬영을 통해 균열진전과정을 분석하였다. An experiment of rapid pressurization-induced crack propagation of solid propellant was conducted by using a windowed test chamber. A pre-cracked specimen of solid propellant is installed in the chamber, and highly compressed nitrogen gas in a accumulator pressurizes the chamber until the chamber pressure reaches set-up pressure to make the chamber depressurization. Pressure-time trace was obtained from the experimental result, and pressurization rate was defined from the trace. In this study, three pressurization rates (64.34, 73.86 and 85.44 ㎫/s) are considered, and propagation lengths are measured. Also, a progression of the crack propagation recorded by a high-speed digital camera is presented.
하재석(Jaeseok Ha),김재훈(Jaehoon Kim),양호영(Hoyoung Yang) 한국추진공학회 2012 한국추진공학회 학술대회논문집 Vol.2012 No.5
고충전 탄성중합체 균열선단에서의 파괴기구를 분석하였으며, 스트립 항복 모델 및 내재결함 모델이 적용되었다. 두 가지 모델의 수정으로부터 고충전 탄성중합체에 대한 파손평가선도의 작성방법이 연구되었다. 고체로켓연료로 사용되는 고충전 탄성중합체의 인장시험 및 파괴인성시험을 수행하였으며, 시험결과로부터 파손평가선도를 작성하였다. 내재결함 모델로부터 작성한 파손평가선도는 스트립 항복 모델로부터 작성한 파손평가선도와의 비교를 위해 정규화되었다. 두 가지 모델로부터 작성한 파손평가선도를 비교한 결과, 내재결함모델을 이용한 파손평가선도가 스트립항복모델을 이용한 파손 평가선도보다 더 보수적으로 파손을 평가하는 것으로 나타났다. Failure mechanisms for a highly filled elastomer were discussed, and the stip-yield and the inherent flaw models were applied to them. Then, failure assessment diagram methods were investigated by means of modified two models. Fracture toughness tests using CCT(center-cracked tension) specimens made of a highly filled elastomer were conducted to generate the failure assessment diagrams. The failure assessment diagram of the inherent flaw model was normalized in order to compare with that of the modified strip-yield model. From the comparison of two failure assessment diagrams, it was found that the failure assessment diagram of the modified inherent flaw model more conservatively assesses the failure than that of the modified strip-yield model.
하재석(Jaeseok Ha),김재훈(Jaehoon Kim),양호영(Hoyoung Yang) 한국추진공학회 2012 한국추진공학회지 Vol.16 No.6
An experiment of rapid pressurization-induced crack propagation of solid propellant was conducted by using a windowed test chamber. A pre-cracked specimen of solid propellant is installed in the chamber, and highly compressed nitrogen gas in an accumulator pressurizes the chamber until the chamber pressure reaches set-up pressure to make the chamber depressurization. Pressure-time trace was obtained from the experimental result, and pressurization rate was defined from the trace. In this study, three pressurization rates (64.34, 73.86 and 85.44 MPa/s) are considered, and propagation lengths are measured. Also, a progression of the crack propagation recorded by a high-speed digital camera is presented.
김연욱(Yeonwook Kim),김재훈(Jaehoon Kim),양호영(Hoyoung Yang),박성한(Sunghan Park),이환규(Hwankyu Lee),김범근(Bumkeun Kim),이성범(Seungbum Lee),곽재수(Jaesu Kwak) 한국추진공학회 2013 한국추진공학회지 Vol.17 No.5
Graphite is commonly used as a solid lubricant leading to low friction coefficient and abrasion. In this study, wear behavior of sealing graphite(HK-6) at elevated temperature was evaluated. Reciprocating wear test was carried out as wear occurred graphite as a seal(HK-6) is positioned between the liner and driving shaft. Variables which are temperature, sliding speed and contact load are set. This study suggest optimized environment conditions through the wear properties of graphite.
하재석(Jaeseok Ha),김재훈(Jaehoon Kim),양호영(Hoyoung Yang) 한국추진공학회 2012 한국추진공학회지 Vol.16 No.5
Failure mechanisms for a solid propellant were discussed, and the stip-yield and the inherent flaw models were applied to them. Then, failure assessment diagram methods were investigated by means of modified two models. Fracture toughness tests using CCT(center-cracked tension) specimens made of a solid propellant were conducted to generate the failure assessment diagrams. The failure assessment diagram of the inherent flaw model was normalized in order to compare with that of the modified strip-yield model. From the comparison of two failure assessment diagrams, it was found that the failure assessment diagram of the modified inherent flaw model more conservatively assesses the failure than that of the modified strip-yield model.
하재석(Jaeseok Ha),김재훈(Jaehoon Kim),정규동(Gyoodong Jung),박재범(Jaebeom Park),양호영(Hoyoung Yang),서보휘(Bohwi Seo) 한국추진공학회 2012 한국추진공학회 학술대회논문집 Vol.2012 No.11
고체추진제 내부의 균열은 연소면적을 증가시키기 때문에 과연소를 발생시키며 로켓의 기능을 상실하거나 파손되는 문제로 이어질 수 있다. 따라서 고체추진제의 설계에서 균열진전에 대한 저항력인 파괴인성의 평가가 요구된다. 하지만 고체추진제의 특성상 복잡하고 심한 비선형 거동을 나타내기 때문에 파괴인성을 측정하는 데에는 많은 어려움이 있다. 본 연구에서는 고체추진제를 선형점탄성 재료로 가정하여 파괴인성을 평가하였다. CCT(Center-cracked Tension) 시험편을 이용한 파괴인성시험을 수행하였으며 점탄성재료에서 나타나는 응력완화현상을 이용한 가상탄성변위를 계산하여 ASTM E399 규격을 통해 파괴인성을 평가하였다. 또한 파괴인성에 대한 시험온도, 시험속도의 영향에 대한 결과를 고찰하였다. Increased burning area generated by cracks in a solid propellant can lead to excessive burning and failure and severe engine failure. Therefore, it is necessary to evaluate fracture toughness of solid propellants. However, it is very difficult to measure fracture toughness of solid propellants because of the nonlinear mechanical behavior. In this study, fracture toughness evaluation of a solid propellant was conducted assuming that the solid propellant is the linear viscoelastic material. Actual displacements from fracture toughness tests using CCT specimens were converted into pseudo-elastic displacements by using stress relaxation characteristics. Also, effects of test temperature and speed on the fracture toughness were considered.
하재석(Jaeseok Ha),김재훈(Jaehoon Kim),정규동(Gyoodong Jung),박재범(Jaebeom Park),양호영(Hoyoung Yang),서보휘(Bohwi Seo) 한국추진공학회 2013 한국추진공학회지 Vol.17 No.2
A crack in a solid propellant increases the area of burning surface, which leads to excessive burning that causes motor failure. Therefore, it is necessary to evaluate fracture toughness of solid propellants. However, it is very difficult to measure fracture toughness of solid propellants because of the nonlinear mechanical behavior. In this study, evaluation of fracture toughness on a solid propellant was carried out under the assumption that the solid propellant is a linear viscoelastic material. Actual displacements from fracture toughness tests using CCT specimens were converted into pseudo-elastic displacements by using stress relaxation characteristics and fracture toughness was evaluated using ASTM E399 standard. Also, effects of test temperature and speed on the fracture toughness were considered.