A New DIC-Based Method to Identify the Crack Mechanism and Applications in Fracture Analysis of Red Sandstone Containing a Single Flaw

As a representative non-interferometric optical technique, the digital image correlation (DIC) can provide full-field displacement and strain measurement for the deformed rocks. However, the standard DIC technique has a limitation in measuring the displacements at the discontinuity and cannot be directly used for identifying the crack mechanism. Thus, a new DIC-based method is proposed for automatically tracing the discontinuities and quantitatively identifying the crack mechanism, i.e. mode I, mode II, and mixed-mode I/II. The new method involves three steps, including displacement measurement from the standard DIC technique, displacement field reconstruction at the discontinuity with the modified subset splitting technique, and post-processing for crack identification and displacement jump measurement. The effectiveness and robustness of the modified subset splitting technique and post-processing method have been verified with the synthetic images and theoretical displacement fields of mode I crack and dislocation. Then, the proposed method is utilized to locate cracks and quantitatively identify the crack mechanism of the initiated cracks in red sandstone containing a single flaw under uniaxial compression. The crack development in the flawed red sandstone specimens is analyzed and the crack types are summarized, in which wing cracks are in mode I, while horsetail cracks and anti-wing cracks are identified as mixed-mode I/II crack. It is shown that the new method avoids some ambiguous identification of crack mechanism and present more objective results.