Papers

@article{munoz-ibanez_acoustic_2021,

title = {Acoustic emission monitoring of mode I fracture toughness tests on sandstone rocks},

author = {Andrea Muñoz-Ibáñez and Jordi Delgado-Martín and Miguel Herbón-Penabad and José Alvarellos-Iglesias},

url = {https://www.sciencedirect.com/science/article/pii/S0920410521005672},

doi = {10.1016/j.petrol.2021.108906},

issn = {0920-4105},

year  = {2021},

date = {2021-10-01},

urldate = {2026-08-06},

journal = {Journal of Petroleum Science and Engineering},

volume = {205},

pages = {108906},

abstract = {A series of mode I fracture toughness tests employing the semi-circular bend (SCB) and the pseudo-compact tension (pCT) methodologies have been performed with two sandstone types and specimens of 50 and 100 mm in diameter. The tests were complemented with the concurrent monitoring of acoustic emission (AE) activity using a multi-sensor array. With the obtained data, we compare and analyse the two testing methods, the mechanical evolution along experiments and the significance of different acoustic emission parameters. The hypocenter location of the AE events allows a better understanding of the processes occurring in the tests and the analysis of properties like amplitude or peak frequencies are valuable complements. Crack modes are assessed using a parameter-based strategy (comparison of the average frequency, AF, and rise angle, RA), and the potential of the Ib-value to discriminate cracking processes in fracture toughness tests is explored. Results show that the pCT method provides more comprehensive and detailed results, both in terms of mechanical information and acoustic emission data. We discuss the applicability of the generally accepted models of small-strain brittle material failure typically applied to compressive tests (including or not including AE data) and further methodological questions of interest when considering AE monitoring in fracture toughness tests.},

keywords = {Acoustic emission, AE parameter analysis, Crack classification, Rock fracture mechanics},

pubstate = {published},

tppubtype = {article}

}

@article{munoz-ibanez_acoustic_2019,

title = {Acoustic emission processes occurring during high-pressure sand compaction},

author = {Andrea Muñoz-Ibáñez and Jordi Delgado-Martín and Elisa Grande-García},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/1365-2478.12691},

doi = {10.1111/1365-2478.12691},

issn = {1365-2478},

year  = {2019},

date = {2019-01-01},

urldate = {2026-08-04},

journal = {Geophysical Prospecting},

volume = {67},

number = {4},

pages = {761–783},

abstract = {Granular materials submitted to uniaxial compression undergo pore space reduction due to mechanisms such as particle rearrangement and grain crushing. These changes in the internal structure of the material release energy in the form of elastic waves that can be detected by sensors sensitive to acoustic emission. In this study, Acoustic emission monitoring with a wavelet-based signal processing technique is used to identify the various mechanisms occurring during high-pressure sand compaction. Particle movement, grain failure, friction between grains and the surface of the compression cell and intergranular friction are studied. Acoustic emission data recorded during these simplified tests are used to characterize each phenomenon. Wavelet transform analyses allow the identification of useful features, making possible frequency discrimination among sliding, rolling, friction and grain fragmentation processes. For instance, we observe that at low stress, grain flow is characterized by the lowest centroid and peak frequencies, while at greater stresses, intergranular friction and grain fragmentation have the higher values. In the tests performed, the stress–strain evolution and final condition of the tested sand are broadly consistent, irrespective of the condition employed: continuous, stepwise or even variable loading rate or temperature. However, Acoustic emission data manifest much more complex behaviour (including thermal, load-rate dependency and delayed fragmentation phenomena) than that suggested by stress–strain relationships. At low stress levels, grain flow (sliding/rolling) is a relevant strain-accommodation mechanism, but so is crushing due to the effect of concentrated forces at the grain contact level. At high stresses, when crushing is generalized, intergranular friction is also a relevant phenomenon due to the increase in the coordination number produced by previous fragmentation.},

keywords = {Acoustic emission, b-value, Grain crushing, Sand compaction, Wavelet transform analysis},

pubstate = {published},

tppubtype = {article}

}