水晶, サファイア単結晶の室温における破壊じん性

抄録

The fracture toughness (K_IC) was measured for quartz and sapphire single crystals as a function of crystal orientation at room temperature. The controlled surface flaw method popularized by J. J. Petrovic et al. was employed in this experiment. Knoop indentor was used to introduce a semicircular microflaw on the surface of the specimen. Then the 3-point bending rupture strength was measured and K_IC was calculated from the flaw size and strength.
Five kinds of crystal orientations, namely (0001), (0110), (0111), (1120) and (1121) planes as fracture surface, were used for quartz, and four crystal orientations, namely (0001), (1100), (1102) and (1120) planes as fracture surface, were used for sapphire. The relation between K_IC and the Young's elastic modulus (E) perpendicular to the fracture surface was investigated.
It is expected from the theoretical consideration that K_IC follows a linear dependence of E. The linear relation between K_IC and E was actually observed for both quartz and sapphire single crystals. This kind of relation was also reported for MgAl₂O₄ single crystal. The K_IC vs. E plot shows different lines for different crystals, namely quartz, sapphire and MgAl₂O₄. As a consequence, it is concluded that the proportional constant of this relation is dependent on the crystal structure.