Papers by Keyword: ATJ Graphite

Abstract: The rocket nozzle throat is exposed to combustion gas of a high temperature. Therefore, it is important to select suitable material for the nozzle which can maintain its structural integrity at a high temperature and to evaluate the material for proper rocket nozzle design. ATJ graphite, as the candidate material for rocket nozzle throat, is studied. In this study, an experimental method to evaluate compressive fracture behavior of ATJ graphite is presented. In particular, the effects of specimen size, temperature and heating time on compressive strength were investigated. Three types of specimens were used in uniaxial tests at room temperature, where the ratios of diameter to length are 1/2 of ASTM standard specimen, one of type I specimen and 1/0.8 of type II, respectively. Also, two kinds of specimen, which were coated using antioxidant and non-coated respectively were tested at elevated temperature to investigate temperature dependency of compressive strength.

Abstract: The purpose of the present study is to evaluate thermal shock properties of the ATJ graphite using laser irradiation techniques. Cracks of thermal shock specimens are initiated by maximum tensile stress field. Thermal shock resistance of the ATJ graphite is correlated with thermal parameter and mechanical property. To simulate the thermal stress conditions of rocket nozzle throat for the evaluation of the thermal shock resistance of ATJ graphite, the laser irradiation was applied at the central area of disk specimen. Thermal shock resistance was related to the geometry, the maximum stress, and the thermal and mechanical property. Also the analyses of transient temperature and thermal stress were performed by the finite element method with nonlinear code ABAQUS. Analyses were specially performed for several kinds of shape to determine the minimum power density which could be cracked the specimen. The shape of the thermal shock specimen which was cracked under the lower power density was obtained and the result will be proved to the test.

Abstract: Graphite has been developed as heat resistant material. To apply a reliable structural design using graphite, it is very important to investigate thermal shock characteristics. The common experimental methods of thermal shock fracture toughness are quenching and arc discharging heating methods. This paper describes experimental technique to evaluate the thermal shock fracture toughness using laser irradiation and proposes that a critical value of laser power can be a measurement to evaluate heat resistant materials. The laser source is CO₂ laser having maximum power of 4.0kW. The range of laser beam is from 1.0 to 2.7 kW and the beam duration is fixed at 1sec. K and C type thermocouples were used to measure the temperature distribution of a thermal shock fracture toughness specimen. In this study, the temperature distribution of specimen surfaces and critical laser power was investigated. After test, the surface phenomenon of specimen is examined using radiography and SEM. It is concluded that the critical laser power causing fracture can be the major factor of thermal shock fracture toughness of ATJ graphite.