Acoustic and Electromagnetic Emissions as Precursor Phenomena in Failure Processes

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.