Damage assessment of a sandwich composite panel by means of digital image correlation

Different studies have demonstrated that vibration characteristics are sensitive to debonding in composite structures. Nevertheless, one of the main restrictions of vibrations measurements is the number of degrees of freedom (DOF) that can be acquired simultaneously. Recent studies have shown that it is possible to use high-speed three-dimensional digital image correlation (DIC) techniques for full-field vibration measurement. Some of the advantages of using DIC measurement for debonding assessment are: i) measuring the vibration over the full surface of an object allows detecting small changes that were unseen with conventional methods, ii) a higher spatial resolution allows computing damage indices with more precision, and iii) a high-speed 3D DIC is a non-contacting system that does not add mass to the structure. Therefore, the properties of the structure are not altered by the measurement system. The present article investigates the application of DIC measurements to assess debonding of sandwich composite panels made of carbon fibre skins and Nomex honeycomb core. A new algorithm to assess damage that combines the Gapped Smoothing method and mode shape strains is proposed. The numerical and experimental results are compared with the conventional Gapped Smoothing approach that uses mode shapes curvatures. The results indicate that the proposed approach based on strains works better in the presence of experimental noise.