Fracture analysis of marble specimens with a hole under uniaxial compression by digital image correlation

To investigate the effects of pre-fabricated holes with different geometries, including size, shape and inclination angle, on the strength and fracture behavior of rock materials, a series of uniaxial compressive tests were conducted on prismatic marble specimens containing a circular or an elliptical hole using a servo-hydraulic machine synchronized with a charge-coupled device (CCD) camera. Digital image correlation (DIC) was applied to record and analyze the deformation and fracturing process of marble. Experimental results combined with theoretical analysis indicate that the geometries of the internal hole are important factors affecting the strength of marble and also the boundary tangential stress distribution. The specimen with a higher tangential compressive stress concentration coefficient will have a lower UCS values. Observations show that the evolution of deformation and fracturing process of marble specimens can be visually displayed by the apparent displacement and strain fields. The propagation of cracks is a progressive development of high major principal strain zones, and the process of damage accumulation, crack initiation and propagation of rock at different stress stages can be well reflected by DIC. When the stress increases to 78.2% of peak value, critical cracks initiate in the tensile stress concentration zones. The progressive process of “open-close-reopen” of tensile cracks was quantitatively studied by the tensile strain of the specimens. It was found that the propagation of tensile cracks surrounding the hole in marble specimens was mainly affected by the nucleation and propagation of strain localization zones.