Exploring the operational limits of a bolometric camera for thermoelastic stress measurementes using a photonic reference camera

Abstract

Image analysis-based measurement techniques are gaining popularity thanks to their ability of measuring different kinds of mechanical fields without interfering with the measurand. Thermoelastic Stress Analysis is a full field, non-contact technique that uses IR images and the principle of thermoelasticity to measure stress distributions. The low amplitude of the temperature variations and the high frequency excitations required, make it mandatory to use fast and expensive IR imaging systems. Using systems based on micro-bolometers instead of photonic sensor, could significantly reduce the cost of the instrumentation. The aim of this study is to understand how to tune the acquisition parameters of a bolometric thermal camera (i.e., the length of the thermal video) and set the right excitation frequency, to match the stress measurement obtained using a state of art photonic thermal camera. The stress concentration around the hole of a PVC sample was used to quantify the difference between the measurement results obtained by the two IR systems. The results showed how having more frames allowed to obtain more detailed maps of stress distribution and to reduce the gap between the bolometric camera and the reference one. The gap increased when the sample was tested with a frequency near the limit set by Nyquist’s theorem.