Stress redistribution and stress drop often coincide with fracture processes. The two experiments that were chosen for our b-value analysis generate failure processes with the corresponding stress drops and stress redistributions. Using acoustic emission analysis, the acoustic waves emitted from the different fracture areas are recorded. The cumulative frequency-magnitude distribution, which leads to the b-value, was originally used in seismology to characterize earthquake populations. Concerning acoustic emissions, the b-value decreases with increasing stress levels. Therefore, it was possible to determine the start of the arise of macro-cracks over time using the b-value analysis. Furthermore, a possible application in a monitoring procedure is suggested.
Acoustic emission (AE) techniques can be used for the investigation of local damage in materials.Compared to other observation techniques one advantage is the recording of the damage process during the entire load history without any disturbance to the specimen. This is somehow unique and permits for high-resolution studies of the time dependend failure of materials including precise determinations of the beginning of fractures and their consecutive progression. There are only a few other experimental techniques in fracture mechanics allowing for similar detailed observations of materials' time and spatial behaviour. Moreover, these techniques allow a calibration of experiment and simulation comparing for example the output of Finite ElementModelling with AE data analysis. This paper deals with some experimental results obtained during fracture mechanical experiments at concrete specimens demonstrating the capabilities of quantitative AE techniques.
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