Continuous Nonlinear Ultrasonic Monitoring of Rock: Advances in Experimental Setup and Data Acquisition

ABSTRACT: Ultrasonic Non-Destructive Testing (NDT) techniques have been successfully used as viable alternatives to traditional stress-strain monitoring methods for tracking damage progression and characterising crack damage stress thresholds. This study focuses on the application of the Scaling Subtraction Method (SSM) a nonlinear ultrasonic testing (NLUT) technique to continuously monitor damage progression in marble under uniaxial compression until failure. To address the limitations in current research, this study provides a rationale for the selection of excitation waveform and excitation frequency, identifying the chirp excitation waveform as superior to the square wave, and establishing 1 MHz as more effective than 2.25 MHz for the rock under study. Additionally, a modified LabVIEW data acquisition system was developed to enable continuous SSM monitoring, achieving alternating low- and high-voltage ultrasonic excitations at 1 Hz. The findings reveal that the evolution of the ultrasonic nonlinearity indicator at increasing stress levels demonstrates SSM's effectiveness in actively monitoring rock damage progression, providing a more dynamic and detailed understanding of cracking behavior compared to traditional methods.