Evaluation and improvement of digital image correlation uncertainty in dynamic conditions

Abstract

Dealing with a moving target causes a motion effect (i.e. blurring) on the acquired images. This factor is an important source of measurement uncertainty while exploiting the Digital Image Correlation (DIC) technique. Therefore, the present study aims to evaluate and improve DIC uncertainty in dynamic conditions in the case of translating target. The study focuses on 2D DIC. In the case of 3D DIC similar problems arise, and therefore a complete understanding of two dimensional conditions will be of great help for further studies which deal with 3D conditions. The whole work can be divided into two main parts. In the first part, two different methods to simulate the motion effect on a reference image are proposed, discussed and validated. These methods allow simulating the acquired images in a real dynamic test and estimating the measurement uncertainty caused by the motion effect. The validation is performed by conducting several harmonic vibration tests with an electromagnetic shaker. In the second part of the study a numerical technique is proposed to estimate the motion effect present in an acquired image. This technique gives two main advantages. First of all, since the motion effect itself has a known influence on the uncertainty of measurement (first part of the study), we can predict the DIC׳s uncertainty by just having an acquired image. Furthermore, this numerical technique is used in the last part of this work to improve the performances of DIC in dynamic applications. In this way the bias error and the uncertainty of measurements were considerably decreased.