Similarity matrices as a new feature for acoustic emission analysis of concrete

The acoustic emission signal contains information about the fracture process which emits the signal and its travel path to the recording sensor. This is expressed in the signal's shape. Estimating the cross correlation function or the magnitude squared coherence function between several signals of clustered events, leads to information about the similarity of these signals, i.e. about the fracture processes and the travel paths. It is possible to use the signal's original shape or to calculate the envelope by the Hilbert transform or to use only a small window around the onset of the signal. With the help of a similarity matrix it is possible to investigate very quickly changes in the physical properties of the ray path of events from one cluster. I.e. changes concerning the dimension of the fracture area or internal stress redistributions become visible. The similarity analysis can be used to identify true acoustic emissions from artefacts and it can be used to reduce the number of events which must be localized to characterize the failure behaviour. Furthermore, the results can be surveyed by other fracture analysis procedures.