Analyzing the Potential Application of Low-Cost Digital Image Correlation in Direct Shear Test

Nowadays, Digital Image Correlation (DIC) has become a frequently used optical technique for testing lab materials due to its nature of non-contact method, allowing for full-field displacements and strains to be accurately measured. The purpose of this study is to examine the potential employment of DIC in performing the standard direct shear test by using a modified box to observe and measure the shear properties of a soil sample. Accessible tools (e.g., a consumer grade DSLR camera) and DIC open-source software were employed in this study in order to monitor every portion of the speckled pattern during deformation and tracking the relative displacements. While it is often difficult to separate the relative contributions of individual error sources in any optical technique, we propose the use of two different validation methods for assessing the accuracy of DIC: the noise-floor and the direct comparison with a second trusted source, like transducers. The results of the conducted study demonstrate that the DIC technique implemented on a properly prepared direct shear laboratory setup opens up new possibilities for the effective and accurate analysis of deformations in soil materials under direct shear loading conditions. The calculations of the noise floor of the setup and speckled pattern in terms of the mean and distribution of the displacements showed validated results with STD of 0.001 and 0.0012 mm for the horizontal and vertical planar components, respectively. The displacements measured by DIC showed good agreement with the results of the transducer with an average error of 0.1 mm.