Optical system for microscopic observation and strain measurement at high temperature

A system of optical microscopy has been developed for high-temperature direct observation and strain measurement. Observations at high temperatures are carried out using a UV CCD camera and UV illumination while thermal radiation is cut off by a UV light transmission filter. Observation of a Vickers indentation on polycrystalline alpha-Al2O3 revealed that sufficient image contrast was maintained up to 1400 degrees C. The potential of the proposed system for strain measurement via digital image correlation was evaluated through measuring the thermal strain of polycrystalline alpha-Al2O3; the obtained coefficient of thermal expansion agreed well with the reported values.