Criticality Hidden in Acoustic Emissions and in Changing Electrical Resistance during Fracture of Rocks and Cement-Based Materials

Acoustic emissions (AE) due to microcracking in solid materials permit the monitoring of fracture processes and the study of failure dynamics. As an alternative method of integrity assessment, measurements of electrical resistance can be used as well. In the literature, however, many studies connect the notion of criticality with AE originating from the fracture, but not with the changes in the electrical properties of materials. In order to further investigate the possible critical behavior of fracture processes in rocks and cement-based materials, we apply natural time (NT) analysis to the time series of AE and resistance measurements, recorded during fracture experiments on cement mortar (CM) and Luserna stone (LS) specimens. The NT analysis indicates that criticality in terms of electrical resistance changes systematically precedes AE criticality for all investigated specimens. The observed greater unpredictability of the CM fracture behavior with respect to LS could be ascribed to the different degree of material homogeneity, since LS (heterogeneous material) expectedly offers more abundant and more easily identifiable fracture precursors than CM (homogenous material). Non-uniqueness of the critical point by varying the detection threshold of cracking events is apparently due to finite size effects which introduce deviations from the self-similarity.

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Studies of Fracture Processes in Cement-Based Materials under Compression with Microtomography and Computer Vision

10.21236/ada337781 ◽

1997 ◽

Author(s):

Surendra P. Shah ◽

Eric N. Landis ◽

Denis T. Keane

Keyword(s):

Computer Vision ◽

Cement Based Materials ◽

Fracture Processes

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Towards early warning of gravitational slope failure with co-detection of microseismic activity: the case of an active rock glacier

Natural Hazards and Earth System Science ◽

10.5194/nhess-19-1399-2019 ◽

2019 ◽

Vol 19 (7) ◽

pp. 1399-1413 ◽

Cited By ~ 3

Author(s):

Jérome Faillettaz ◽

Martin Funk ◽

Jan Beutel ◽

Andreas Vieli

Keyword(s):

Early Warning ◽

Slope Failure ◽

Acoustic Emissions ◽

Warning System ◽

Heterogeneous Material ◽

Rock Glacier ◽

Simple Method ◽

Distributed Sensors ◽

New Strategy ◽

Co Detection

Abstract. We developed a new strategy for disaster risk reduction for gravitational slope failure: we propose validating on a case study a simple method for real-time early warning of gravity-driven failures that considers and exploits both the heterogeneity of natural media and characteristics of acoustic emissions attenuation. This method capitalizes on co-detection of elastic waves emanating from micro-cracks by a network of multiple and spatially distributed sensors. Event co-detection is considered to be surrogate for large event size with more frequent co-detected events marking imminence of catastrophic failure. In this study we apply this general method to a steep active rock glacier, a natural heterogeneous material sharing all relevant properties of gravitational slope failure, and demonstrate the potential of this simple strategy for real world cases, i.e., at slope scale. This new strategy being theoretically valid for all types of failures, it constitutes a first step towards the development of a new early warning system for gravitational slope failure.

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Acoustic Emission Monitoring of the Turin Cathedral Bell Tower: Foreshock and Aftershock Discrimination

Applied Sciences ◽

10.3390/app10113931 ◽

2020 ◽

Vol 10 (11) ◽

pp. 3931 ◽

Cited By ~ 2

Author(s):

Amedeo Manuello Bertetto ◽

Davide Masera ◽

Alberto Carpinteri

Keyword(s):

Structural Integrity ◽

Regional Scale ◽

Acoustic Emissions ◽

B Value ◽

Masonry Building ◽

Cumulative Number ◽

Value Analysis ◽

Integrity Assessment ◽

Static And Dynamic Analysis ◽

Bell Tower

Historical churches, tall ancient masonry buildings, and bell towers are structures subjected to high risks due to their age, elevation, and small base-area-to-height ratio. In this paper, the results of an innovative monitoring technique for structural integrity assessment applied to a historical bell tower are reported. The emblematic case study of the monitoring of the Turin Cathedral bell tower (northwest Italy) is herein presented. First of all, the damage evolution in a portion of the structure localized in the lower levels of the tall masonry building is described by the evaluation of the cumulative number of acoustic emissions (AEs) and by different parameters able to predict the time dependence of the damage development, in addition to the 3D localization of the AE sources. The b-value analysis shows a decreasing trend down to values compatible with the growth of localized micro and macro-cracks in the portion of the structure close to the base of the tower. These results seem to be in good agreement with the static and dynamic analysis performed numerically by an accurate FEM (finite element model). Similar results were also obtained during the application of the AE monitoring to the wooden frame sustaining the bells in the tower cell. Finally, a statistical analysis based on the average values of the b-value are carried out at the scale of the monument and at the seismic regional scale. In particular, according to recent studies, a comparison between the b-value obtained by AE signal analysis and the regional activity is proposed in order to correlate the AE detected on the structure to the seismic activity, discriminating foreshock, and aftershock intervals in the analyzed time series.

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