Digital Image Correlation accuracy: influence of kind of speckle and recording setup

Abstract

Digital Image Correlation (DIC) is a popular optical technique which allows the measurement of displacement and strain fields on an object surface showing a random speckle pattern. To use its extension to 3D cases (called Digital Volume Correlation, DVC), it is often necessary to include particles in the material in order to have a sufficient contrast. However, as these particles are more rigid than the material, it is not sure that the correlation technique is able to follow exactly strains on the speckle pattern made of powder. As the digital recording process by CCD camera and correlation algorithms are the same between 2D and 3D cases, this study is then conducted in 2D cases in order to show the influence of the powder in the speckle pattern on the evaluation of displacement by DIC linked to the choice of the type of interpolation, of CCD cameras and lighting. In displacement tests, only the recording setup seems to have a strong influence on the accuracy of measurements. For strain experiments, powder has an effect on strain measurements over 10%.