No abstract

In this work, we measured the electromagnetic field, given by the moving charges, during laboratory fracture experiments on specimens made of different heterogeneous materials. We investigated the mechanical behaviour of concrete and rocks samples loaded up to their failure by the analysis of acoustic emission (AE) and electromagnetic emission (EME). All specimens were tested in compression at a constant displacement rate and monitored by piezoelectric (PZT) transducers for AE data acquisition. Simultaneous investigation into magnetic activity was performed by a measuring device calibrated according to metrological requirements. In all the considered cases, the presence of AE signals has been always observed during the damage process, whereas it is very interesting to note that the magnetic signals were generally observed only in correspondence to sharp stress drops or the final collapse.

We perform a comparative statistical analysis between the acoustic-emission time series from the ancient Greek Athena temple in Syracuse and the sequence of nearby earthquakes. We find an apparent association between acoustic-emission bursts and the earthquake occurrence. The waiting-time distributions for acoustic-emission and earthquake time series are described by a unique scaling law indicating self-similarity over a wide range of magnitude scales. This evidence suggests a correlation between the aging process of the temple and the local seismic activity.

SUMMARY An experimental analysis has been carried out on the long‐term behaviour of composite specimens and walls made with historical brickwork. The test pieces were subjected both to static and to cyclic loading tests (accelerate static creep) and to freezing‐thawing thermo‐hygrometric tests in order to study the durability of different strengthening mortars. The acoustic emission (AE) monitoring technique was also used to assess the damage localization and to predict the time to failure of the strengthened walls during fatigue tests. The AE is a very effective non‐destructive technique that permits to estimate the amount of energy released during fracture propagation. Damage evolution during fatigue compressive loading, in terms of measured strains and the AE counting number, can be divided into three stages; fatigue life can be predicted from the slope of the AE counting number rate diagram. Starting from an AE monitoring, a special methodology has been developed to predict the service life of creep damaged masonry structures. The novelty of this work consists in the experimental confirmation that the AE technique is able to analyse the creep curves of masonry strengthening mortars. Therefore, it demonstrated that by the AE technique, it is also possible to evaluate the durability of strengthening materials subjected to load histories in the time. Copyright © 2013 John Wiley & Sons, Ltd.

The present research focuses on acoustic emission (AE) and electromagnetic emission (EME) detected during laboratory compression tests on concrete and rocks specimens. We investigated their mechanical behavior up to failure by the AE and EME due to micro‐ and macrocrack growth. Among the tested specimens, a concrete sample was analyzed by applying to its surface both piezoelectric (PZT) transducers for detection of high‐frequency AE waves, and PZT accelerometric transducers for detection of low‐frequency AE (elastic emission or ELE). Besides the high‐frequency AEs, the emergence of low‐frequency ELE just before the failure describes the transition from diffused microcracking to localized macrocracks which characterizes the failure in brittle materials. For all the specimens, a simultaneous analysis of magnetic activity was performed by a measuring device calibrated according to metrological requirements. In all the considered specimens, the presence of AE events has been always observed during the damage process, whereas it is very interesting to note that the EMEs were generally observed only in correspondence with sharp stress drops or the final collapse. The experimental evidence confirms AE and EME signals as collapse precursors in materials like concrete and rocks.