Ultraviolet time-gated active-imaging digital image correlation: A novel solution for ultra-high temperature deformation measurement

Active-imaging digital image correlation (DIC) based on monochromatic illumination and optical bandpass filtering provides a simple and effective approach to measure the surface deformation of test materials and structures at elevated temperatures. However, when the sample temperature exceeds 2000 °C or strong thermal radiation from heating elements is present, the current active-imaging strategy fails to effectively suppress the massive thermal radiation from the heated sample and heating elements. Here, we present an ultraviolet (UV) time-gated active-imaging technique that employs a gated single-photon camera to significantly reduce exposure time and a UV bandpass filter to block most thermal radiation. This combination of UV bandpass filtering in the spectral domain and time-gated imaging at UV wavelengths in the time domain suppresses the enormous thermal radiation from the heated sample and heating source to a negligible level compared with the active illumination. Real-world validations, including full-field thermal deformation measurement of a Ni-based alloy sample, thermal strain measurement at 2800 °C, and tensile strain measurement at 2500 °C of carbon-carbon composite material samples, verified the performance of the proposed method. Beyond its current applications, the ultraviolet time-gated active-imaging DIC method holds promise as a powerful tool for characterizing the thermo-mechanical properties of materials and structures in extremely high-temperature environments.