Similarity of fluctuations of acoustic emissions in natural time

Abstract In the present study, a series of uniaxial compression and three-point bending experiments of marble and cement mortar specimens were carried out under different loading rates until fracture, using specimens of different geometries. During the tests the acoustic activity produced was recorded and as a next step, the energy of the acoustic signals was analysed in natural time. As a result, the variance κ1 of the natural time analysis of the acoustic energy was proven to exhibit an exponential tail as previously found for the order parameter in several equilibrium or non-equilibrium systems. The findings presented here support the use of the κ1 as an order parameter for the acoustic emission events in the last seconds before the failure of the specimens.