Applicability of ultrasonic tomographic technique for progressive damage evaluation in prismatic rock specimen

Several damage processes are associated with the loading of intact rock specimens including closure of existing microcracks, initiation of cracks, and finally development of cracks. Ultrasonic imaging techniques have proven to be very successful in providing relatively high-resolution images of the damage processes in the rock. Ultrasonic velocity tomography is a full-field measurement technique that can help understand the evolution of damage within a brittle rock specimen remotely and non-destructively. Variations in elastic compressional (P-) wave velocity in a rock specimen can be associated with the changes in its elastic properties under mechanical loading at different stages of damage. The objective of this research study was to examine the applicability of ultrasonic tomographic technique for determination of velocity fields in prismatic rock specimens subjected to uniaxial compression. An array of piezoelectric ultrasonic sensors were used to generate and receive elastic waves across the prismatic specimen and a fast LabVIEW-based data acquisition system was used to record the waveforms. By analyzing and comparing the changes in generated velocity tomograms, through tomographic inversion method, the velocity fields in synthetic and natural rocks were determined.