Application of the cluster analysis and time statistic of acoustic emission events from tensile test of a cylindrical rock salt specimen

In a cylindrical rock salt sample under tensile load, two large acoustic emission (AE) clusters have occurred, which are perpendicular to the axial tensile load of the sample. These clusters could be found by a reasonable choice of the primary cluster parameters, which depends mainly on the spatial and temporal density of the events. In comparison with in-situ measurements in salt mines, the size of the primary cluster parameters in rock samples under tensile load is in a few orders of magnitudes lower. Therefore, the primary cluster parameters used for the laboratory investigations were a maximum distance between 4 and 12 mm and a maximum time interval of 0.5-2 min. The method used to investigate the dimension (fracture plane or not?), the spatial position as well as the temporal and spatial correlation of the AE events are described by using two large AE clusters. In addition, the time frequency distribution was applied to the two biggest clusters. The time differences of clustered AE events show a statistical equilibrium distribution, which is a clear evidence for the existance of a Poisson process. That means the events occurred independently and at random.