Cracking of LT Single Crystal Due to Thermal Stress
Noriyuki MIYAZAKI and Naoyoshi KOIZUMI
Abstract:The quantitative estimation of the failure stress of a lithium tantalate(LT) single crystal due to thermal stress was investigated. Circular plate test specimens were heated in a silicone oil bath, then subjected to large thermal stress by room temperature silicone oil. Cracking occurred during cooling. The transient heat conduction analysis was performed to obtain temperature distribution in the test specimen at the time of cracking, using the surface temperatures measured in the test. Then the thermal stress was calculated using the temperature profile of the test specimen obtained from the heat conduction analysis. It is found from the results of the thermal stress analysis and the observation of the cracking in the test specimens that the cracking induced by thermal stress occurs mainly in cleavage planes due to the stress component normal to the plane. As for a size effect of failure stress, large-sized circular plate test specimens show lower failure stress than small-sized ones. Four-point bending tests were also performed to examine the relation between the critical stress for the cracking induced by thermal stress and the four-point bending strength. Several discussions were made for size effect of failure stress from the viewpoint of the WeibullÕs weakest link model. Key Words:Finite element method, Thermal stress, Cracking, Failure stress, Single crystal, Weibull distribution