Timelapse ultrasonic tomography for measuring damage localization in geomechanics laboratory tests

Abstract

Variation of mechanical properties in materials can be detected non-destructively using ultrasonic measurements. In particular, changes in elastic wave velocity can occur due to damage, i.e., micro-cracking and particles debonding. Here the challenge of characterizing damage in geomaterials, i.e., rocks and soils, is addressed. Geomaterials are naturally heterogeneous media in which the deformation can localize, so that few measurements of acoustic velocity across the sample are not sufficient to capture the heterogeneities. Therefore, an ultrasonic tomography procedure has been implemented to map the spatial and temporal variations in propagation velocity, which provides information on the damage process. Moreover, double beamforming has been successfully applied to identify and isolate multiple arrivals that are caused by strong heterogeneities (natural or induced by the deformation process). The applicability of the developed experimental technique to laboratory geomechanics testing is illustrated using data acquired on a sample of natural rock before and after being deformed under triaxial compression. The approach is then validated and extended to time-lapse monitoring using data acquired during plane strain compression of a sample including a well defined layer with different mechanical properties than the matrix.

Reconstructing Underwater Temperature Spatial Distribution Using Ultrasound Tomography

“…Temperature of the right side of the water pool was slightly higher than that of the left side. Circulating water system in the 27m × 14.6m × 4m water pool might cause the temperature change from 19.30 • C to 19.45 • C. Clearly, such a small-scale temperature distribution could not be reconstructed by either using low frequency underwater acoustic technique [4]- [7], [9], [14] or high frequency acoustic tomography [8], [11].…”

“…, the sound speed variation δc j can be reconstructed by solving Eq. (7). We then use the least square method…”

“…Acoustic tomography of ocean climate project was proposed to monitor global ocean temperature [5]. Low frequency acoustic transmission was conducted to obtain temperature variation of arctic ocean water [6] and to monitor heat content across the Mediterranean Sea [7]. Low central frequencies such as 40 Hz, 100-to 200-Hz, and 400 Hz lead to low temporal as well as spatial resolutions of acoustic tomography.…”

History effects in the creep of a disordered brittle material

“…Additionally, the AE in the sample was monitored using two piezoelectric sensors, yielding a catalog of acoustic event energies E AE . The sample was simultaneously monitored with ultrasonic sensing [53] (measurements at 6-min intervals, which are removed from the AE data) using two arrays of ultrasonic transducers to follow the evolution of the attenuation of direct (ballistic) elastic waves within the material, a way to probe internal damage of the sample. See Appendix A for full experimental details.…”

Modern Displacement Measuring Systems Used in Geotechnical Laboratories: Advantages and Disadvantages

“…In a very wide range of applications, non-invasive methods of observing the full field of deformations and displacements include the following methods (based on [ 91 , 92 ]: optical, based on X-rays (X-ray tomography), e.g., [ 7 , 93 , 94 , 95 , 96 ], neutron tomography, e.g., [ 8 , 97 , 98 ], thermography, acoustic and ultrasonic tomography, e.g., [ 99 , 100 , 101 ], Magnetic resonance imaging (MRI), e.g., [ 102 ], Electrical resistivity tomography (ERT), e.g., [ 103 ], Positron emission tomography (PET). …”