2002 Volume 45 Issue 4 Pages 612-619
In order to evaluate the reliability of ceramics under transient thermal stress, thermal shock test equipment was designed and fabricated. Cylindrical specimens made of Si3N4 and SiC were tested by the test equipment. Each specimen was preheated uniformly at 1573K in an electric furnace and then pulled down rapidly into a cooling chamber beneath the furnace. At the same time, it was cooled locally by high-velocity helium gas that was passed through a narrow slit. The transient temperature distributions were measured by optical pyrometers and thermocouples. The moment of fracture was confirmed by the sound of the fracture itself. Fracture originated at the outer surface immediately under the cooling nozzle. Consequently, the average value of nondimensional fracture stress of Si3N4 specimens was about two times that of SiC specimens.