Interevent acoustic emission character of three-point-bending tests on concrete beams by the nearest neighbor distance

Three-point-bending tests on notched concrete beams were performed with real-time AE (acoustic emission) monitoring. Based on the nearest neighbor theory modified from seismology, the minimum interevent distance eta(j)* for every AE event is calculated. The b-value and space fractal dimension are computed to further explore the parameter eta(j)*. The experimental results indicate that eta(j)* values for AE data from threepoint-bending tests show a mixed distribution of background and clustered events, similar to earthquakes induced by fluids, and are considered to be due to the formation of a single main fracture under this loading condition. The real-time difference and real-time interval for every nearest event pair are similar to the lognormal and exponential distributions, respectively. According to eta(j)* combined with the spatial distribution of AE events, eta(j)* is negatively correlated with the fracture trace, which means that AE events with smaller eta(j)* values are closer to the trace. Analyses of b-values and spatial fractal dimensions illustrate eta(j)* ability to smooth the variation curves of these two parameters and clarify their change rules. These observations confirm that eta(j)* is a useful index for illustrating the interevent characteristics of AE data and has significance for analyzing the fracture mechanisms of concrete materials. (C) 2019 Elsevier Ltd. All rights reserved.