Improvement of Ultraviolet Digital Image Correlation (UV-DIC) at Extreme Temperatures

Extreme temperature has increasingly played an essential role in design and operation of various engineering applications including spacecraft re-entry, hypersonic flight, next-generation nuclear reactors, and hot-fire rocket testing. To protect instruments against the harsh environments, it is preferable to use non-contacting measurements when monitoring the integrity of those mechanical structures. Digital Image Correlation (DIC) is a popular method which uses digital cameras in order to track motion thanks to images acquired before and after deformation. Displacements and strains are plotted over a full-field region which is conducive to identify highly risky zones. At high temperature, objects emit light which interferes with image acquisition. It is known that the emitted light is considerably suppressed when images are taken at very short wavelengths such as ultraviolet (UV). This dissertation will investigate the importance of exposure time, which is a significant factor when determining the camera sensitivity, on the uncertainty of UV-DIC measurements. Through examining the exposure time, this dissertation is intended to give insights for users when performing DIC at high temperature in both pre-testing conditions and on-going testing. In addition, the dissertation will discuss a specific phenomenon of pattern inversion which is occasionally reported in high temperature DIC measurement. Under this phenomenon, due to differences in emissivity of refractory paint and the background material, portions of the object which appear dark at room temperature instead appear bright at high temperature, and vice versa. The dissertation will explain the physical principle behind pattern inversion and introduce alternative solutions to evade the pattern inversion.With the aforementioned contributions, the dissertation is expected to improve the UV-DIC technique intensively and extensively