“Integrated” digital image correlation for residual stress measurement

Residual stress measuring by optical methods has been proposed by several authors in the past years; nevertheless the technique is still confined to optical laboratories: indeed the large sensitivity of the optical methods allows measuring very low stress values with high reliability, but these advantages are counter-balanced by the high sensitivity to vibrations, which makes very difficult performing the measurements outside of optical laboratories. Digital Image Correlation (DIC) is a possible alternative: indeed this technique is much less affected by vibrations, but its sensitivity is quite low, thus negatively affecting the accuracy of results. This work proposes a variant of Digital Image Correlation, known as iDIC (integrated DIC), to perform residual stress measurement. Since this approach directly integrates in the formulation the hole drilling shape functions, it overcome most of the problem of standard DIC; in this way it is possible to obtain accurate results without using interferometric techniques.