抄録
The quantitative estimation of the failure stress of a lithium niobate (LN) single crystal due to thermal shock was investigated. Cylindrical test specimens of 50mm diameter and 10mm thickness were obtained from a LN bulk single crystal by pulling in the c-axis direction. A test specimen was heated to about 470K in an oil bath, and then thermal shock was applied to it by pouring room temperature silicon oil; cracking occurred during cooling. The surface temperature was measured by using thermocouples. A temperature profile of the test specimen was obtained from an axisymmetric finite element program for unsteady heat conduction analysis, using the measured surface temperature as the boundary condition. Then the thermal stress was calculated from a three-dimensional finite element program for thermal stress analysis, using the temperature profile of the test specimen obtained from heat conduction analysis. The program for thermal stress analysis takes into account the anisotropy of a LN single crystal, such as of elastic constants and thermal expansion coefficients, as well as their temperature dependence. Four-point bending tests of a LN single crystal were carried out to examine the relationship between thermal shock cracking and failure due to mechanical load.
