Crackling noise and its dynamics in fracture of disordered media

Laboratory experiments on fracture yield ample evidence on the stick-slip or intermittent character of the dynamics of failure. We discuss the experimental evidence about such intermittency based on in particular acoustic emission (AE), the detection and analysis of ultrasound which reflects the elastic energy released in the fracture process. The main points are the statistical characterization of AE, the correlations that possibly exist in AE signatures or time series, and the universality of such features upon changing material and fracture setting (loading mode, loading rate and so forth). We also discuss implications on theory and on materials science via failure time or ultimate strength prediction.