Acoustic Emissions at High and Low Frequencies During Compression Tests in Brittle Materials

Abstract

The damage process in a concrete specimen subjected to uniaxial compression test is investigated by detection of the propagating elastic waves because of micro-and macrocrack growth. Besides the high-frequency acoustic emissions (AEs), the presence of low-frequency elastic emissions (ELEs), from 1 to 10 kHz, is detected just before the specimen failure. A spectral analysis of the ELEs is performed by measuring with a calibrated transducer the local acceleration of the specimen surface. Quantitative information about the macrocrack effects in terms of released energy is thus obtained. Furthermore, the evolution of damage is followed through the analysis of the amplitude distribution of AE and ELE signals, distributed according to the Gutenberg-Richter (GR) statistics.KEY WORDS: acoustic emissions, b-value analysis, elastic emissions, fracture precursors, lowfrequency Ó

On the puzzling feature of the silence of precursory electromagnetic emissions

“…More specifically, electromagnetic emissions (EME) and acoustic emissions (AE) in a wide frequency spectrum ranging from the kHz to the MHz bands are produced by opening cracks, which can be considered as the so-called precursors of general fracture. Recently, improvements in the MHz-kHz EME technique have permitted a real-time monitoring of the fracture process (Fukui et al, 2005;Kumar and Misra, 2007;Chauhan and Ashok Misra, 2008;Baddari et al, 1999Baddari et al, , 2011Baddari and Frolov, 2010;Lacidogna et al, 2010;Schiavi et al, 2011;Carpinteri et al, 2012). However, the MHz-kHz electromagnetic (EM) precursors are detectable not only at the laboratory but also at the geological scale; a stressed rock behaves like a stress-EM transducer (Sadovski, 1982;Hayakawa and Fujinawa, 1994;Gokhberg et al, 1995;Hayakawa, 1999Hayakawa, , 2009Hayakawa and Molchanov, 2002;Eftaxias et al, 2007Eftaxias et al, , 2011Eftaxias, 2012;Molchanov and Hayakawa, 2008).…”

Acoustic Emission Monitoring and Failure Precursors of Sandstone Samples under Various Loading and Unloading Paths

“…First, the confining pressure was loaded to the design value (10,20,40, and 50 MPa). Second, the confining pressure remained unchanged, and the axial stress was loaded to 80% of the peak strength obtained from conventional triaxial tests.…”

“…During this process, the strain energy is continuously released in the form of the elastic wave, which is referred to as the acoustic emission (AE). It is helpful to investigate the failure mechanism of rock materials to study the AE characteristics during the failure process and the relationship between the AE parameters and rock fracture [6][7][8][9][10][11].…”

Signal frequency distribution and natural-time analyses from acoustic emission monitoring of an arched structure in the Castle of Racconigi

“…These studies should hopefully contribute to solving the main problems of earthquake prediction and the remaining life assessment of structural elements. In particular, the latter is a crucial issue for researchers involved in restoration projects of historic monuments with damaged and cracked structural elements, which can benefit from the use of nondestructive monitoring techniques for the structural integrity assessment Schiavi et al, 2011;Lacidogna et al, 2015a). AE monitoring seems to be suitable for this kind of structural monitoring as it provides information on the internal state of a material without altering state of conservation of statues, monuments and fine artworks.…”