The critical exponents of fracture precursors
The acoustic emission of fracture precursors is measured in heterogeneous materials. The statistical behaviour of these precursors is studied as a function of the load features and the geometry. We find that the time interval between events (precursors) and events energies are power law distributed and that the exponents of these power laws depend on the load history and on the material. In contrast, the cumulated acoustic energy presents a critical divergency near the breaking time. The critical exponent is independent, within error bars, by all the experimental parameters.