Reflection transformation calibration for mirror-assisted multi-view digital image correlation system using fluorescent speckle patterns

Mirror-assisted multi-view digital image correlation (MV-DIC) is a simple-to-implement DIC technique for panoramic kinematic field measurements of regular-sized specimens. In the practical implementation of mirror-assisted MV-DIC, accurate reflection transformation calibration of the planar mirrors is considered as a pivotal step. In this work, we propose to use fluorescent speckle patterns fabricated on the mirrors to calibrate their reflection transformation matrices, which can fully utilize the camera's spatial resolution and simplify the calibration processes. The fluorescent speckle patterns on the mirrors do not interfere with the virtual object surfaces using a regular blue-light stereo-DIC system. However, under the illumination of ultraviolet light, the fluorescent speckle patterns can be captured and used to calibrate the position and orientation of the planar mirrors. The practicality and efficacy of the fluorescent speckle pattern-based calibration method are validated by profile measurement and translation tests, and an application in a four-point bending experiment is also demonstrated.