Fluorescent 2D Digital Image Correlation With Built‐in Coaxial Illumination for Deformation Measurement in Space‐constrained Scenarios

Abstract

An advanced two-dimensional digital image correlation (2D-DIC) using active imaging and telecentric imaging has been proposed to overcome the problems of out-of-plane motion and ambient light variation. Here, the technique is further improved by combining built-in coaxial illumination and telecentric fluorescent imaging to provide quality 2D-DIC measurement even in space-constrained scenarios. This improved 2D-DIC firstly excites the fluorescent speckles on the specimen surface using an ultraviolet light source through built-in coaxial illumination, and then employs a monochromatic telecentric imaging system to capture the images of the excited speckles. By tracking the movements of fluorescent speckles using DIC, full-field displacements and strains can be retrieved. For validation, the quality of speckle images captured by three different 2D-DIC systems was firstly evaluated, proving that the proposed fluorescent 2D-DIC can eliminate the specular reflections and acquire speckle images with the best quality. A uniaxial tensile test of an Al alloy specimen in an environmental chamber and thermal strain measurement of a polymethylmethacrylate sample in a water bath device were performed using the established system, further confirming the practicality of the proposed method. With the improved performance, compactness, and ease of use, this fluorescent 2D-DIC is expected to be widely applied in future research.