Evaluation of Thermal Shock Fracture Toughness for ATJ Graphite Using Laser Irradiation Method

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.