Evaluation of progressive damage in barre granite using ultrasonic velocity tomography and digital image correlation

Full-field measurement techniques have the significant advantage of taking measurements along the complete specimen specially assisting in the characterization of heterogeneous rocks. This research's objective was therefore to evaluate and characterize the damage occurring inside uniaxially-loaded Barre granite specimens using two non-destructive full-field measurement techniques, namely, the ultrasonic velocity tomography (UVT) and two-dimensional digital image correlation (2D-DIC). Piezoelectric ultrasonic sensors were used to generate and receive elastic P-waves across the prismatic specimen and a fast LabVIEWbased data acquisition system was used to record the waveforms. Ultrasonic tomographic inversion method was utilized to generate sectional velocity field tomograms, at different levels of uniaxial stress compared to the failure stress level. By analyzing and comparing the changes in velocity tomograms, the initiation and growth of cracking in the rock specimens were monitored. The low-velocity zones in the tomograms were associated with the location and extent of damage in the specimen. The 2D-DIC technique was used to determine the displacement and strain across the specimen surface by analyzing the digital images acquired during the uniaxial loading. 2D-DIC was able to identify the damage occurring in the form of crack formation and propagation and highlighted the importance of using combined full-field measurement techniques.