Evaluation of Optical Window Integrity Under Wall Heat Flux of Scramjet Intake

The structural integrity of sapphire optical windows was numerically and experimentally evaluated under the wall heat flux of the scramjet intake. The considered heating profile was [Formula: see text] during 60 s, and the heating profile for the numerical and experimental approaches was the same. A numerical study was performed using the finite element method; the numerical results predicted that the maximum temperature of the optical window under the heating condition was about 600 K, the maximum principal stress was less than the strength of the sapphire, and the failure of the optical window would not occur based on the brittle Coulomb–Mohr material failure theory. The heating test was performed using an electrical heater under the heating condition, and the morphology was investigated using scanning electron and atomic force microscopies. The experimental results indicated that no cracks or fractures occurred on the surface of the optical window after the heating test, except for a slight change in the shape and roughness of the microstructure.