High-speed And High-temperature Digital Image Correlation Method In Experimental Study Of Thermal Shock

When aircraft is working, its surface and engines suffer serious thermal shock leading to the fracture of material easily. The process of thermal shock is transient and temperature changes drastically, current study is limited to the qualitative analysis of comparing the shape of the sample before and after thermal shock, without quantitative analysis aim at the process. A new method aiming at high-temperature and high-speed testing was established based on the existing technology of digital image correlation (DIC). The new method was used to test the mechanical properties of material in the course of thermal shock successfully, which could provide evaluation index for the resistance of thermal shock.Noise levels of high-speed camera were estimated by shooting stationary objects at different frequencies. Results shown that camera noise levels keep stable at different frequencies and different times; the error is small enough for DIC method. High-speed photography system's distortion was researched by measurement of a rigid body displacement. A calibration is needed when the system is working below 1040fps, while the frequencies over 2000fps the distortion can be ignored.To produce speckles which can sustain high temperature at the surface of materials is crucial to high-temperature mechanical measurement. A new method for making high-temperature speckles was invented by silvering. Furthermore, a grinding process was explored by using sandpaper, sharpening stone and rasp, which was applied in ZrB2 successfully. When material is heated to a certain temperature, radiation becomes strong and will cover the speckle field. This problem was solved by designing a filter with mid-peak position for transmission is 450nm and the full-width value is 40nm.A droplet-quenching thermal shock experimental platform was built. Through a new way, four different crack patterns were observed: linear, semi-circular, wavy and mixed crack. By application of high-speed and high-temperature DIC, the course of the glass thermal shock was clearly observed and its displacement field was computed with increment of 0.25ms. Results showed that the displacement field changed drastically and intricately, stress concentration was observed obviously. Furthermore, Finite element simulation of principal stress was in good agreement with the experimental results.An oxyacetylene emergency-heating experimental platform was built autonomously. The structure of substrate and coating was shocked underΔT = 2000℃, a quantitative calculation of the strain evolution of the substrate, coating surface and the lateral side was achieved. In extreme high temperature conditions, the strain distribution and evolution was obtained. The strain is very high and some domains up the order of 10^-2. Also, the thermal shock of the ZrB2 was realized byΔT = 1600℃on the aforementioned platform.