Damage analysis of thermal-shock failure in isostatically pressed carbon-bonded refractories for continuous casting of steel

In refractory engineering, evaluating thermal shock resistance is essential. Yet, for some applications, standardized tests may not fully characterize the processes of damage development and failure. To analyze failure mechanisms in refractories enabling continuous casting of steel a novel thermal shock test was developed. The test simulates ascending heating of severity typical for the service conditions. Sample geometry is representative of service pieces. Several isostatically pressed carbon-oxide materials of different brittleness at failure were tested for in situ monitoring. An infrared temperature measurement, contact extensometers, as well as non-contact methods of digital image correlation and Laser Doppler Vibrometry were used.Regarding the novelty of Laser Doppler Vibrometry for damage assessment in refractories, this method was validated by a series of stress-strain tests. The damage was also quantified by stress-strain data employing cyclic stress-strain protocols. During the thermal shock tests, materials of different brittleness demonstrated a wide range of possible failure modes, including instantaneous cracking throughout the sample thickness, gradual crack growth, and damage formation without pronounced crack localization. The modes of failure corresponded with the standardized thermal shock index ranking. In-situ non-destructive tests were especially beneficial for the analysis of non-brittle failure.