Issue 50

D. Triantis et alii, Frattura ed Integrità Strutturale, 50 (2019) 537-547; DOI: 10.3221/IGF-ESIS.50.45 537 Focused on the research activities of the Greek Society of Experimental Mechanics of Materials Fracture precursor phenomena in marble specimens under uniaxial compression by means of Acoustic Emission data Dimos Triantis University of West Attica, Department of Electrical and Electronic Engineering, Laboratory of Electronic Devices and Materials, 250 Thivon Avenue, Campus 2, 122 44, Athens, Greece triantis@uniwa.gr, http://orcid.org/0000-0003-4219-8687 Stavros K. Kourkoulis National Technical University of Athens, School of Applied Mathematical and Physical Sciences, Department of Mechanics, Laboratory for Testing and Materials, 5 Heroes of Polytechnion Avenue, Theocaris Bld., Zografou Campus, 157 73 Athens, Greece stakkour@central.ntua.gr, https://orcid.org/0000-0003-3246-9308 A BSTRACT . Marble specimens are subjected to a specially designed stepwise loading protocol, in an attempt to detect fracture precursor phenomena taking advantage of Acoustic Emission (AE) data. The analysis is carried out in terms of the number of acoustic hits recorded and the time evolution of the improved b-value (I b -value), the cumulative energy of the acoustic signals and the F-func- tion. During the stage of increasing load, intense acoustic activity is detected as the corresponding stress reaches the transitional phase from the linear to the nonlinear mechanical response of the material. When the stress is stabilized at levels exceeding 95% of the material’s compressive strength, the acoustic activ- ity is drastically reduced. During the first seconds of the stress stabilization stage the reduction follows an exponential law. Special attention is paid to the phases, where the occurrence of AE hits shows a strong increase. During these phases acoustic signals of low frequency and high RA are recorded, indicating that the micro-cracking process is of shear rather than of opening mode. K EYWORDS . Acoustic Emission; Marble; Compression; I b -value; F-function; Micro-cracking classification. Citation: Triantis, D., Kourkoulis, S.K. Frac- ture precursor phenomena in marble specimens under uniaxial compression by means of Acou- stic Emission data, Frattura ed Integrità Strut- turale, 50 (2019) 537-547. Received: 21.01.2019 Accepted: 18.05.2019 Published: 01.10.2019 Copyright: © 2019 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION he mechanical response of brittle heterogeneous materials under compressive loading and the damage accumulation within their mass, which unavoidably accompanies the loading procedure, are of great interest in a wide range of engineering applications. Of particular interest are the quantitative description of the damage mechanisms activated and the early prediction of upcoming catastrophic failure. In this direction, series of damage assessment techniques have T