Abstract : As part of the BMDO-funded Sapphire Statistical Characterization and Risk Reduction (SSCARR) program, thin circular disks of seeker window-grade sapphire are thermally fractured using a CO2 laser. The resulting test data will be used to benchmark window failure models being developed under SSCARR that will utilize mechanical bend-bar data obtained for sapphire with the same processing and pedigree. A significant advantage of thermal stress testing over mechanical strength testing is the avoidance of contact stresses. This is particularly important for sapphire, which is susceptible to load-point stress concentrations that can induce twinning and premature failure from rhombohedral shear. The susceptibility to twin formation and rhombohedral shear fracture in the absence of contact loads is an important question being investigated as part of this effort. The experimental test procedure and data reduction are described, and thermal fracture test results obtained to date are summarized.