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최훈석(Hoonseok Choi),김재훈(Jaehoon Kim),오광근(Kwangkeun Oh),문순일(Soon-il Moon),구송회(Songhoe Koo) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
Graphite material has been widely used in rocket nozzle throat due to its excellent thermal properties. However, compared with typical structural material, graphite is relatively weak with respect to both strength and toughness due to its quasi brittle behavior and gets oxidized at 450°C. Therefore it is important to evaluate mechanical properties of this material for application. This study presents an experimental method to investigate fracture behavior of ATJ graphite at elevated temperature. In particular, temperature, loading and oxidation conditions are major parameter to investigate the relationship of strength and fracture characteristics. Uniaxial tests are conducted in accordance with ASTM in the range of R.T to 1,000°C. Fractography analysis of fractured specimens are carried out using SEM
최훈석(Hoonseok Choi),김재훈(Jaehoon Kim),김연욱(Yeonwook Kim),서보휘(Bohwi Seo),문순일(Soonil Moon) 한국추진공학회 2014 한국추진공학회지 Vol.18 No.4
Graphite is commonly used for rocket nozzle. The purpose of the present study is to evaluate compression fracture behavior of ATJ graphite. Uniaxial compression test is conducted in accordance with ASTM C 695 in the range of R.T to 900°C. The size effects of specimen on the compressive strength and fracture behavior were investigated. Two types of cylindrical specimen, i.e., where the diameter to length ratio is 1:2 (ASTM C 695 specimen) or 1:1, were tested at room temperature.
최훈석(HoonSeok Choi),김기홍(Ki-Hong Kim),전태영(TaeYoung Jeon) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
This paper presents a dynamic analysis of a high speed flight-vehicle as it is launched from rail guided structure. The important performance of the rail guided structure is that the flight-vehicle should be separated from the rail in a stable condition at the initial stage. Rail guided structure model studied in this paper is composed of rail structures, spring loaded detent and night-vehicle. The flight-vehicle has two hangers, one of which was constrained by detent mechanism prior to launch. As the vehicle moves, the forward hanger presses against the slope face of the detent level. In order for the vehicle to be moved, enough load must be applied to overcome the detent spring force. In this paper, launching mechanism and dynamic behavior of night-vehicle were studied. Analysis of the dynamics of the rail guided structure and flight-vehicle were simulated using MBD(multi body dynamic) simulation. AS a results of MBD simulation, detent force, contact force, roll/pitch/yaw motions of launched vehicle at the initial stage were plotted.
로켓 노즐목에 사용하는 ATJ 그라파이트의 압축 파단 특성
최훈석(Hoonseok Choi),김재훈(JaeHoon Kim),김연욱(Yeonwook kim),서보휘(Bohwi Seo),문순일(Soon-il Moon) 한국추진공학회 2013 한국추진공학회 학술대회논문집 Vol.2013 No.12
본 연구의 그라파이트는 로켓 노즐 목 재료로 많이 사용되는 것으로써 온도, 가공성 및 무게 측면에서 유리하다. 하지만 고온 및 고압상태에서 고속으로 취성파괴 되므로 설계 시 구조적 안정성을 충분히 확보해야 한다. 본 연구에서는 로켓 노즐목에 이용되는 ATJ 그라파이트에 대해서 상온 및 고온에서 ASTM C 695에 준하여 압축 시험을 수행하였다. 또한 시편의 단면적 변화에 의한 압축 강도 및 파단 특성을 분석하였다. Graphite is commonly used for rocket nozzle throat. The purpose of the present study is to evaluate compression fracture behavior of ATJ graphite. Uniaxial compression test is conducted in accordance with ASTM C 695 in the range of R.T to 900˙C. The size effects of specimen on the compressive strength and fracture behavior were investigated. Two types of cylindrical specimen, i.e., where the diameter to length ratio was 1:2(ASTM C 695 specimen) or 1:1 , were tested at room temperature
나성현(Seonghyeon Na),최훈석(Hoonseok Choi),오광근(Kwangkeun Oh),김재훈(Jaehoon Kim) 한국추진공학회 2015 한국추진공학회 학술대회논문집 Vol.2015 No.5
입자강화 복합재는 균열진전에 대한 저항력인 균열저항거동의 평가가 요구된다. 하지만 입자강화 복합재의 특성상 복잡하고 심한 비선형 거동을 나타내기 때문에 균열저항에 대한 저항을 나타내는 기준인 파괴인성을 측정하는데 많은 어려움이 있다. 본 연구에서는 입자강화 복합재를 선형 점탄성 재료로 가정하여 파괴인성을 평가하였다. 비선형 파괴거동 시험인 WST(Wedge splitting test) 시험편을 이용한 파괴인성시험을 수행하였으며 변형 전과 변형 후의 이미지를 비교하여 변위, 변형률을 측정하는 기법인 디지털이미지 상관법(Digital image correlation)을 이용하여 균열저항거동 평가에 필요한 데이터를 추출하였고, 변형률장을 가시화 하였다. 또한 ASTM E399 규격을 통해 파괴인성을 평가하였고, 시험온도는 50℃에서 ?60℃로 진행하였다. A particulate reinforced composite is required estimation of fracture crack resistance behavior about resisting power for crack growth. However, fracture toughness is hard to measure because of non-linear behavior. In this study, evaluation of crack resistance behavior was carried out under the assumption that the Particulate reinforced composite is a linear viscoelastic material. Wedge splitting test was performed on fracture toughness. Data for crack resistance behavior and strain fields obtained through the digital image correlation that is technique compared image of transformation. Also, it evaluated fracture toughness through ASTM E399 standard and the experiments are conducted in the range of temperature 50 ℃. to ?60 ℃.
고체 추진용 입자강화 복합재의 정적 균열 저항 거동 평가
서보휘(Bohwi Seo),최훈석(Hoonseok Choi),김재훈(Jaehoon Kim) 한국추진공학회 2014 한국추진공학회지 Vol.18 No.5
Particulate reinforced composite is composed of hard particles and polymer matrix. This material has been widely applied for engineering industry such as automobile, construction and aerospace. For the safe application, it is important to assess crack resistance behavior. Especially in aerospace industry, crack could cause significant problem when the material is used for solid rocket fuel. Therefore, it is inevitable to estimate the characteristics of the crack propagation. In this study, crack propagation tests were conducted using particulate reinforced composite under crosshead rate 2.54 mm/min in the range of temperature -60℃to 60℃. The strain contour of surface for specimen was generated using digital image correlation method.
DIC에 의한 입자강화 복합재 추진제의 균열저항 특성평가
나성현(Seonghyeon Na),최훈석(Hoonseok Choi),오광근(Kwangkeun Oh),김재훈(Jaehoon Kim) 한국추진공학회 2015 한국추진공학회지 Vol.19 No.6
In this study, it is evaluated for fracture toughness to analyze crack resistance properties of particulate reinforced composite propellant. Fracture toughness test using WST specimen is conducted by temperature conditions from 50℃ to –60℃. Evaluation method for fracture toughness calculated using an equation suggested by ASTM E399 with linear elastic fracture mechanics. From these result, splitting loads and stress intensity factors of propellant increase according to decrease of test temperature. Also, the strain fields of specimen surface using digital image correlation increase as temperature decreased from 50℃ to –40℃, but it sharply decreases at –60℃ because of brittle behavior.