Thermal shock fracture behavior of wave-transparent brittle materials in hypersonic vehicles under high thermal flux by digital image correlation

During diving, high orbit maneuver, or target detection and positioning, a hypersonic vehicle will experience high thermal flux. Aerodynamic heating will cause intense thermal shock to the antenna window and radar dome, which are usually made of brittle materials that are transparent to electromagnetic waves and are critical to the mission of target positioning and hitting. Therefore, determination of the time to fracture of the brittle materials under high thermal flux is of great significance. In this study, thermal shock tests were performed on two brittle materials, i.e., SiO ₂ and Al ₂ O ₃ , using a quartz lamp radiator test system with a maximum thermal flux of 1.5MW/m ² . The difference between the pre-set and actual thermal fluxes for the tests was smaller than 1.0%. The time to fracture was determined for the two brittle materials by employing the digital image correlation method to capture and analyze changes in speckle images of the specimen’s surface. The speckle image analysis also revealed variations in the surface strain values (ε _x and ε _y ) prior to fracture. The test results provide important input for the safety and reliability design of radar domes and other electromagnetic wave-transparent signal detection and positioning components of hypersonic vehicles when subjected to high thermal fluxes.