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.
Highlights
Nowadays, full-field measurements of shape and displacements occurring on surface elements are accessible thanks to optical techniques based on digital cameras [1,2]
Two-dimensional Digital image and correlation (DIC) computes speckle perpendicular to the optical axis while fringe projection (FP) computes the surface displacement along the optical axis displacements in a plane perpendicular to the optical axis while FP computes the surface from the lateral shifting of the projected fringes
This work presents and evaluates two improvements in the experimental methodology used for 3D displacement measurement performing fringe projection together with 2D-digital image correlation
Summary
Full-field measurements of shape and displacements occurring on surface elements are accessible thanks to optical techniques based on digital cameras [1,2]. These techniques have provided interesting applications in experimental mechanics to observe and explain the mechanical behaviour of solids and the validation of theoretical and/or numerical models. Digital photoelasticity [3,4,5], shows a high level of sensitivity in the direct measurement of the shear strain in photoelastic materials. Electronic speckle photography and interferometry techniques [2,6] offer high sensitivity for detecting displacements
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