Evaluation of an Ultrasonic Method for Damage Characterization of Brittle Rocks

Illumination of Damage in Intact Rocks by Ultrasonic Transmission‐Reflection and Digital Image Correlation

“…The mid‐height of the specimen was chosen for ultrasonic imaging, as this region is least sensitive to the constraints applied at the specimen ends by the loading platens, and hence is more representative of the specimen deformation (Tang & Hudson, 2010). This is also consistent with the laboratory‐scale setup employed in several studies on the ultrasonic‐based characterization of rock damage, for example, Jones (1952), Gupta (1973), Lockner et al (1977), Sayers et al (1990), Wulff et al (1999), Fortin et al (2007), Luong (2009), Ghazvinian (2015), and Shirole et al (2017), Shirole, Walton, Ostrovksy, Masoumi et al (2018), Shirole, Walton, Ostrovsky, Hossein et al (2018), Shirole et al (2019a, 2019b), Shirole, Hedayat et al (2020). Compressional P‐wave ultrasonic pulses with a period of 1 μs were transmitted and reflected through the specimen, for which Videoscan longitudinal wave transducers (V‐103; diameter of 13 mm and central frequency of 1 MHz) from Olympus NDT, Inc. were used.…”

“…A negative square pulse (300 V) produced by a pulse generator from Olympus NDT, Inc. every 200 μs served as the active source of the compressional ultrasonic signals (in both T‐mode and R‐mode). The T‐mode and R‐mode ultrasonic signals were digitized at a sampling frequency of 100 MHz and were acquired near‐continuously at 1 Hz (for details, refer to Shirole et al, 2017, and Shirole, Hedayat et al, 2020). For R‐mode LUT, the source transducer acted as both the source and receiver of the reflected ultrasonic signals, whereas in T‐mode, the source and receiver transducers performed as the source and receiver of the transmitted ultrasonic signals, respectively (Figure 1b).…”

“…The presence of the plastic film ensures that there is no loss in the honey couplant present at the rock‐transducer contact area due to damage‐induced dilation in the rock volume (at different levels of stress), which is critical for associating the ultrasonic signal variations with the material damage. Before the start of the uniaxial experiments, the transducer‐rock assembly with honey coupling was allowed to equilibrate for 1 hr, to ensure that any time‐dependent artifacts related with the transducers and the specimen coupling can be neutralized (Shirole, Hedayat et al, 2020). Following the honey‐coupling period, the SG specimens were uniaxially loaded, and the full T‐mode and R‐mode ultrasonic signals were acquired using the LabVIEW‐controlled data acquisition system in‐sync with the 2‐D DIC procedure.…”

Thermal Infrared Radiation and Laser Ultrasound for Deformation and Water Saturation Effects Testing in Limestone

“…These methods comprise destructive methods involving load testing under different loading conditions [11,12] and semi-destructive mechanical tests with simultaneous measurement of acoustic emission [13,14]. Non-destructive in situ and laboratory methods for inspecting natural materials are addressed in [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], including thermal control [16][17][18][19][20], multispectral optical remote sensing [21], ground penetrating radar [22,23], ultrasonic inspection [25,26], gamma-ray logging [27], terahertz spectroscopy [28], X-ray tomography [29,30], neutron radiography [31], and others [32].…”

“…However, it would be more efficient to use this method together with ultrasonic diagnostics so as to comprehensively assess the condition and internal structure of geomaterials. Conventional ultrasonic flaw detectors and tomographs operate, as a rule, at a certain resonance frequency [24][25][26], which makes it difficult to determine the geometry and location of different-scale defects. The use of piezoelectric transducers exciting and receiving broadband ultrasonic signals results in a sharp decrease in radiated power and a significant decrease in sensitivity, which means that the dynamic range becomes narrower.…”