ESTIMATION OF THERMAL-SHOCK FRACTURE-TOUGHNESS OF SI3N4

An infrared radiation heating method was proposed previously as anew t echnique for estimating thermal shock strength and thermal shock fract ure toughness of ceramics using a thin-circular disk with or without a n edge crack, heated by infrared rays at the center with a constant he at flux. In this paper, thermal shock fracture toughness was measured by the above method in four kinds of silicon nitride. Temperature dist ributions, thermal stresses and stress intensity factors for the speci mens were also analyzed considering the temperature dependent thermal conductivity, thermal diffusivity and thermal expansion of the materia ls. The experimental results show that the highest value of thermal sh ock fracture toughness was observed in the material having the higher thermal conductivity, which was developed by growing the grains and de creasing the amount of the grain boundary phase.