bQuantitative evaluation of fracture processes in concrete by the use of improved -value

Shiotani, Tomoki; Yuyama, Shigenori; Li, Z.W.; Ohtsu, Masayasu

doi:10.1016/b978-008043717-0/50031-3

Cited by 32 publications

(26 citation statements)

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“…The most important phenomenological law describing the amplitude scaling of emission events is the GR law [15–21]: where N (≥ m ) is the number of events with magnitude M ≥ m occurring in the specimen volume during a given time interval, and b (or ‘ b ‐value’) indicates the damage level reached in the specimen. The magnitude of AE events is defined in dB through the relation log( V max /1 μ V); the magnitude of ELE events is defined in dB through the relation 20 log( a max /1 μ m s −2 ).…”

Section: Ae and Ele Frequency–magnitude Statisticsmentioning

confidence: 99%

“…The b ‐value, being correlated with the degree of damage localisation, is recognised as a useful tool for damage level assessment. In general terms, the damage process moves from diffused microcracking to localised macrocracks as the material approaches impending failure, and the b ‐value decreases from values in the range (1.5–2.5) at the initial stages to values approximately 1, and less, during propagation of the through‐going fracture [16–21].…”

Section: Ae and Ele Frequency–magnitude Statisticsmentioning

confidence: 99%

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

Schiavi

Niccolini

Tarizzo

et al. 2011

Strain

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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

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Section: Ae and Ele Frequency–magnitude Statisticsmentioning

confidence: 99%

Section: Ae and Ele Frequency–magnitude Statisticsmentioning

confidence: 99%

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

Schiavi

Niccolini

Tarizzo

et al. 2011

Strain

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“…Thereby, the slope of the cumulative frequency-amplitude distribution plot(s) of AE is affected. In order to avoid or filter such low-amplitude, unwanted AE, researchers proposed Ib-value analysis, and it is a relatively new approach that is computed using recorded AE peak amplitude data [27,39,40,[48][49][50].…”

Section: Frequency-amplitude Distribution Relationmentioning

confidence: 99%

Acoustic Emission During Flexural Deformation of Reinforced Concrete Under Incremental Cyclic Loading

Sagar

Rao²

2016

Journal of Testing and Evaluation

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Acoustic emissions (AE) released during the flexure tests of reinforced concrete (RC) beams under incremental cyclic loading conditions in the laboratory were subjected to improved b-value (Ib-value) analysis. Ib-value has been reported to be useful to detect, track, and investigate the various stages of micro-cracking and macro-crack damage in concrete. Further, Ib-value has been found to be free from the influence of monitoring conditions. We observed in the present study that the Ib-value began to decrease with the beginning of the formation of new micro-cracks, and then stabilized ($1.0) and finally dropped down sharply to a very low value marking the onset of macro-crack damage and its growth in concrete. Additionally, when the Ib-value decreased, AE with steep rise angle (RA) values were noticed with the formation and growth of micro-cracks in concrete. On the contrary, the average frequency (AF) of AE events was found to decrease during the micro-and macrocracking stages of the test beams. These experimental observations of AE-based Ib-value combined with RA and AF were useful for the detailed study of flexural deformation and the failure of concrete at various stages in the laboratory and, perhaps, in situ conditions as well.

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“…As discussed earlier, AE ''b values'' have previously been used to assess AE events and their occurrence over time. For example, the b value (given by the second constant in the empirical relationship of the number of events, N, of a size greater than or equal to magnitude M, log 10 N = a)bM,) is often seen to drop during the enlargement of cracks (e.g., SHIOTANI et al, 2000). Such empirical analysis can also be applied to acoustic emission data, after multiplication by 20 to correct for the fact that AE amplitudes are measured in decibels rather than the logarithmic peak amplitude of the Richter scale (HATTON et al, 1993).…”

Section: Event Location and Rnmentioning

confidence: 99%

Monitoring Fracture Propagation in a Soft Rock (Neapolitan Tuff) Using Acoustic Emissions and Digital Images

Hall

Sanctis

Viggiani

2006

Pure appl. geophys.

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Sudden and unexpected collapses of underground cavities below the city of Naples (Italy) represent a serious safety hazard. The collapses occur due to the detachment of large blocks from the cavity roofs, walls and pillars, often a long time after the original quarry excavation has been completed. It is recognised that existing discontinuities, e.g., fractures, play an important role in the failure process by inducing local stress-concentrations and reducing the overall material strength. The larger fractures, which ultimately lead to collapse occur through interaction, propagation and coalescence of these discontinuities. This paper presents recent results of experiments carried out on natural, dry specimens of Neapolitan finegrained tuff to investigate the mechanisms involved in sample failure. A better understanding of fracture development and rock bridge behaviour is gained through a combination of AE and photographic monitoring in an experimental program considering samples with artificial pre-existing heterogeneities, which simulate the in situ discontinuities. For a range of rock bridge geometries the mechanisms and timing of different stages of the failure process are identified and characterised. The results show that, in general, a classical description of failure, for samples without artificial flaws or with only a single flaw, is followed: (1) crack closure; (2) linear stress-strain response and crack initiation with stable crack growth; (3) crack damage and unstable crack growth leading to failure. For samples with two artificial pre-existing flaws the third phase is split into two parts and failure of the sample occurs only after both the unstable propagation of external wing cracks and coalescence of the internal cracks in the bridge. In terms of the timing and duration of each phase, it is seen that phases 1 and 2 have little dependence on the flaw configuration but phase 3 seems to depend directly on this. In particular the angle in rock bridge between the inner tips of the pre-existing flaws, b, plays a key role: phase 3 is shorter for b = 120°than for b = 105°. These differences are due to the different modes of coalescence in the rock bridge. For b = 105°the total failure is preceded by bridge rotation, which appears to take longer than the simpler mode of failure for b = 120°. It has only been possible to determine the time ranges of interest using the AE signatures, whilst the photographs allow the fracture geometry evolution to be described. Additionally the frequency character of AE events is investigated and shown to have significant potential for characterisation of AE source types and thus failure processes.

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bQuantitative evaluation of fracture processes in concrete by the use of improved -value

Cited by 32 publications

References 1 publication

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

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

Acoustic Emission During Flexural Deformation of Reinforced Concrete Under Incremental Cyclic Loading

Monitoring Fracture Propagation in a Soft Rock (Neapolitan Tuff) Using Acoustic Emissions and Digital Images

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