Evaluation of Global and Local Digital Volume Correlation for Measuring 3D Deformation in Rocks

The investigation of localized deformation in rocks at the laboratory scale can yield valuable insights into the internal structures and mechanisms of shear zones and compaction bands that impact the permeability characterization and failure mechanisms of rocks. Combined with high-resolution X-ray computed tomography and in situ loading, the digital volume correlation (DVC) technique is an effective tool for mapping the deformation in rocks. This technique is mainly divided into two categories: subset-based local DVC (L-DVC), used for rocks because of its straightforward implementation and high efficiency, and finite-element-based global DVC (G-DVC), which usually offers better accuracy because of the continuity among element nodes. In this study, we compared the accuracy and precision of these two DVC approaches for five rocks and discussed two factors important for accuracy, namely element/subset size and microstructure. The results show that performance of the G-DVC is better than that of the L-DVC, albeit at the expense of computational efficiency, especially for smaller subset sizes. An indentation test on red sandstone was performed to further demonstrate the feasibility of the two methods. This study aims to supplement the lack of research on the two DVC approaches for rocks and provides a reference for subsequent related research.