High-temperature strain measurement using active imaging digital image correlation and infrared radiation heating

A technique for non-contact and full-field high-temperature strain measurement of a sample subjected to radiation heating using active imaging digital image correlation is described in this work. A high-performance quartz lamp heater system was designed to reproduce transient thermal environments experienced by hypersonic vehicles. The digital images of the test sample surface at various temperatures are captured using a novel active imaging optical system based on a combination of monochromatic light illumination and bandpass filter imaging. Subsequently, the captured images are processed by a robust reliability-guided displacement tracking algorithm with an automatic reference image updating scheme to extract full-field thermal deformation. With the improvements made in both the imaging system and correlation algorithm, the de-correlation problem of speckle patterns caused by the thermal radiation and surface oxidation of the heated test object are effectively addressed, enabling reliable deformation measurement in extremely high temperature environments. The performance of the proposed active imaging digital image correlation technique is verified by two experiments: (1) measurement of the uniform thermal strains of a chromium-nickel austenite stainless steel sample which is heated from room temperature to 1300 degrees C, and (2) measurement of the non-uniform thermal strain fields of a woven C/SiC composite at 1550 degrees C. The test results show that the active imaging digital image correlation is an easy-to-implement yet effective optical technique for high-temperature strain measurement, and has great potential in characterizing thermo-mechanical behaviour of materials and structures for hypersonic vehicles. Limitations and potential improvements of the present technique are also discussed.