Studying feasibility of applying digital image correlation algorithms on infrared images

Full-field optical methods constitute a valuable class of tools in experimental mechanics which have been applied, in the last decades, to a number of different problems. in the last years, in conjunction with the advancements in computing a new full-field approach is becoming more and more widely adopted. This is the so called Digital Image Correlation (DIC) approach which is, in its essence, based on algorithms of image analysis and comparison allowing to extract information about, shape and strain/displacement field of the object under study. The core of the approach consists in studying the correlation of each sub-portion of the reference image with each sub-portion of the image of the loaded object. This can be conveniently done if a random, isotropic, high-contrast pattern is present on the surface to be analyzed. Such a kind of pattern can be naturally present on the object under analysis or artificially sprayed on it. Also temperature measurements can get great advantages from adopting full-field approaches allows to get the entire temperature field instead of a single average temperature value. It is well known, in fact, that by using infrared (IR) thermography it is possible to evaluate point by point the temperature of a body with a known emissivity by using an infrared detector and a proper collecting lens to record the radiation emitted in the infrared spectrum. In many situations both strain field and temperature field have to be recorded in order to have a full comprehension of the thermo-mechanical behaviour of the analyzed component. For example, in IR thermography and ESPI were used to detect the thermomechanical behaviour of a power transistor. In this paper we study the feasibility of using a simplified approach for measuring displacement/strain field and temperature field at once. This relies on performing digital image correlation analysis directly on thermal images (t-DIC). This would allow, whenever it is possible to prepare to surface with a random pattern of emissivity or when it is naturally present on the sample to analyze, to get in a simple way the complete thermomechanical response of the sample. Implementation of a combined IR-2D DIC system is here shown; a calibration procedure is presented and validated and finally results on a case study are illustrated.