Study and generation of optimal speckle patterns for DIC

Digital Image Correlation (DIC) - also referred to as white light speckle technique - is an optical-numerical full-field measuring technique, which offers the possibility to determine in-plane displacement fields at the surface of objects under any kind of loading. For an optimal use of the method, the object of interest has to be covered with a speckle pattern. The present paper studies the efficiency of a random speckle pattern and its influence on the measured in-plane displacements with respect to the subset size. Four different speckle patterns are selected with different speckle sizes and spectral content. Subsequently, each speckle pattern image undergoes a numerically controlled deformation, which is measured with digital image correlation software. Both imposed and measured displacements are compared and it is shown that the size of the speckles and its spectral content combined with the size of the used pixel subset, clearly influences the accuracy of the measured displacements.