Acoustic Emission and fracture energy dissipation in notched concrete beams subjected to three-point bending tests

In this study, three-point bending (TPB) tests on notched concrete beams having different size, have been carried out to evaluate the influence of propagation distance on the AE parameters. The most representative AE parameters have been measured by sensors at different distances from the source, in order to obtain detailed information on the type of cracks as well as on the source localization. The waves frequency and the rise angle are used to discriminate the prevailing cracking mode from pure opening or sliding [1]. The cumulated number of AE events and their amplitude are used to compute the signal energy. Each signal recorded during the bending test by the first sensor has been compared with the same signal captured by the other one. For all concrete beams, an average value of the AE parameters for each sensor has been made. The AE parameters average value indicates how important the propagation distance between the two sensors is for the AE analysis. However, AE waveform parameters are effected by strong attenuation and distortion due to propagation through an inhomogeneous medium, which should not be neglected in laboratory and, in particular way, on real structures. The AE results obtained from the three-point bending tests prove that the variation of the AE parameters during the loading process strictly depends on the specimen damage. A decrease in frequency may be provoked by large cracks progress both during tensile and sharing process, while an increase in AE signal energy content is detected approaching the final failure. A distinct element numerical model of the beam is described and used to model the energy dissipation during the three point bending test. The model accounts for the mesostructure of plain concrete in the region closed to the central notch. Each aggregate is modeled together with the bonding of the matrix. In this way it is possible to simulate numerically the concrete crushing, as well as the tensile cracking at the aggregate interface or through the matrix and, eventually, through the inclusions [2-4]. The model is able to simulate the Acoustic Emission localization and statistics, in addition to the fracture energy dissipation, allowing for a better understanding of the ongoing phenomena.