Accurate displacement measurement by correlation of colored random patterns

The use of colored random patterns for the calculation of the correlation coefficient is proposed to improve the accuracy of the digital image correlation technique for displacement measurements. The colored random pattern is created by spraying color paints on the surface of a sample. Then, not only the displacement distributions but the displacement gradients are determined using a set of color images before and after deformation. The effectiveness is demonstrated by applying the proposed method to the displacement measurement of rigid body rotation, and the results are compared with those obtained from the monochromatic images. The results show that the use of the color image in digital image correlation improves the measurement accuracy both of the displacements and the displacement gradients. In addition, the smaller size subset can be used for the calculation of the correlation. The proposed technique is effective in the fields of experimental mechanics and experimental stress analysis.