A high resolution DIC technique for measuring small thermal expansion of film specimens

In this study, we develop a high-resolution digital image correlation (HRDIC) platform for measuring small thermal deformation of film specimens with some negative factors eliminated which may affect the measurement accuracy, such as image noise, heat radiation and out-of-plane deformation. Firstly, to reduce the image noise level, the images acquired by the high-speed camera at a frame rate of 1000 fps at each temperature are first averaged and then analyzed by linear digital image correlation with bias correction. Secondly, a pneumatic device is added on the one side of the oven to eliminate the distortion effect of heat radiation from the heated oven on acquired images. Finally, by using a reference material with a known coefficient of thermal expansion (CTE) with the test sample during the thermal loading and imaging, the effect of out-of-plane deformation on in-plane thermal strain measurement is corrected. Based on above improvements in the experimental set-up and post digital image processing, the proposed HRDIC technique is demonstrated to be able to reliably measure the very low CTEs of thin silicon film and Invar-like material.

► Images acquired by high-speed camera are averaged to reduce the image noise level. ► A pneumatic device is used to eliminate the distortion effect of heat radiation on images. ► By using a reference material, the effect of out-of-plane deformation is corrected. ► Based on above improvements, HRDIC is used to measure the low CTEs of films.