Similarity of fluctuations in critical systems: Acoustic emissions observed before fracture

Abstract

Here, we study the scaled distributions for the variance κ1 of natural time χ when analysing the energy time-series of acoustic emission recorded when marble and cement mortar specimens were subjected to mechanical loading until fracture. It is shown that the κ1 scaled distributions exhibit – for at least three orders of magnitude – a characteristic exponential tail like that previously found for the order parameter in equilibrium (e.g., two-dimensional Ising model), and in non-equilibrium (e.g., turbulent flow) critical systems as well as in seismicity. The presented findings, which are also compared to those coming from the non-conservative Olami–Feder–Christensen earthquake model and the Burridge–Knopoff train model, advocate for the use of κ1 as an order parameter for the acoustic events preceding failure in a fashion similar to that in the case of seismicity.