RGB Colour Encoding Improvement for Three-Dimensional Shapes and Displacement Measurement Using the Integration of Fringe Projection and Digital Image Correlation

Abstract

Three-dimensional digital image correlation (3D-DIC) has become the most popular full-field optical technique for measuring 3D shapes and displacements in experimental mechanics. The integration of fringe projection (FP) and two-dimensional digital image correlation (FP + DIC) has been recently established as an intelligent low-cost alternative to 3D-DIC, overcoming the drawbacks of a stereoscopic system. Its experimentation is based on the colour encoding of the characterized fringe and speckle patterns required for FP and DIC implementation, respectively. In the present work, innovations in experimentation using FP + DIC for more accurate results are presented. Specifically, they are based on the improvement of the colour pattern encoding. To achieve this, in this work, a multisensor camera and/or laser structural illumination were employed. Both alternatives are analysed and evaluated. Results show that improvements both in three-dimensional and in-plane displacement are obtained with the proposed alternatives. Nonetheless, multisensor high-speed cameras are uncommon, and laser structural illumination is established as an important improvement when low uncertainty is required for 2D-displacement measurement. Hence, the uncertainty has been demonstrated to be reduced by up to 50% compared with results obtained in previous experimental approaches of FP + DIC.

Three-Dimensional Digital Image Correlation Based on Speckle Pattern Projection for Non-Invasive Vibrational Analysis

“…The method is based on projected 3D-DIC and is capable of non-invasively identifying the full-field mode shapes and natural frequencies of a UAV wing made of composite material, which could potentially benefit structural dynamics and health monitoring applications [54]. Previous studies described fringe patterns [55,56], laser speckle [41,57] or a combination of both [40] to create a non-invasive pattern for full-field vibration measurement in DIC applications. In a recent study, Felipe-Sesé et al [40] proposed a combination of a fringe pattern, a laser speckle and a single-camera DIC to measure the three-dimensional shapes and the associated field of displacements of a plate excited by a shaker.…”

“…Previous studies described fringe patterns [55,56], laser speckle [41,57] or a combination of both [40] to create a non-invasive pattern for full-field vibration measurement in DIC applications. In a recent study, Felipe-Sesé et al [40] proposed a combination of a fringe pattern, a laser speckle and a single-camera DIC to measure the three-dimensional shapes and the associated field of displacements of a plate excited by a shaker. The authors validated their results with theoretical predictions and obtained a maximum error near the edges of the structure of 4.95%.…”

“…In the last few years, two main directions have been described in the state-of-the-art for the development of non-invasive projected patterns: fringe patterns and laser speckle patterns. Fringe patterns have been combined with speckle patterns and a single camera for DIC in two dimensions and mechanical trials that required a low-frequency ratio of images [39,40]. The random granular effect in the laser speckle pattern has its origin in the high coherence of the light source that is projected to the sample and in the decorrelation when the sample moves in the out-of-plane direction.…”

Three-Dimensional Shape and Deformation Measurements Based on Fringe Projection Profilometry and Fluorescent Digital Image Correlation via a 3 Charge Coupled Device Camera

“…Subsequently, the technique was employed by Luis [ 31 ] in a vibration test. To circumvent stroboscopic issues, Luis [ 32 ] and colleagues proceeded to substitute projection fringes with laser fringes. Notably, Wu Zhoujie [ 33 ] and associates employed three-step phase shifting and gray code technology to infer the 3D shape of an object, subsequently matching it via DIC.…”

Digital Image Correlation with a Prism Camera and Its Application in Complex Deformation Measurement

“…The idea is to separate the red and blue channels of a single-color camera using a light-splitting prism, and then form binocular stereo vision through reflectors [ 18 ]. In addition, Luis et al [ 19 ] synthesized the characteristic stripe and speckle pattern into color coding. They improved the measurement accuracy of 3D displacement and in-plane displacement due to the addition of phase information.…”