The Brittle-Ductile Transition in Porous Limestone Imaged by X-Ray Computed Tomography and Digital Image Correlation

Abstract

We studied the brittle-ductile transition in three porous carbonates, Indiana, USA, Majella, Italy, and Leitha, Austria, with porosity ranging between 16 and 31%. A series of triaxial experiments were performed at room temperature, constant strain rate, and at effective pressures ranging from 5 to 150 MPa. Several sets of X-ray Tomography images were acquired before and after deformation. 3D digital image correlation (DIC) was performed on the images of the intact and deformed samples. The use of 3D-volumetric DIC allowed us to map out the subtle development of strain localization associated with the transition from brittle faulting to cataclastic flow in the three limestones. Our observations showed that strain localization may develop at relatively small axial strains of ~1%, in both the brittle faulting and transitional regimes. In Majella limestone (porosity = 31%), the localized deformation involved both shear and compaction. Compaction bands were only observed in less cemented samples of Leitha limestone.