13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- 0,E+00 1,E+04 2,E+04 3,E+04 4,E+04 5,E+04 6,E+04 7,E+04 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 Cumulative AE-event and AE-hit Displacement (mm) AE-Hits S1 AE-Hits S2 AE-event 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 Event / Hit rate Displacement (mm) Event/Hit S1 Event/Hit S2 Event/Average Hit S1-2 (a) (b) y = 74,28%x R² = 99,80% 0,E+00 2,E+04 4,E+04 6,E+04 8,E+04 1,E+05 1,E+05 1,E+05 2,E+05 0,E+00 5,E+04 1,E+05 2,E+05 2,E+05 3,E+05 Events Energy (aJ) Average Energy of total hits (aJ) 0,0E+00 5,0E+04 1,0E+05 1,5E+05 2,0E+05 0 20 40 60 80 100 120 140 160 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 Energy (aJ) Visual crack length (mm) Displacement (mm) Crack length (mm) Events Energie (aJ) (c) (d) Figure 5. AE data. a) Cumulative AE-event and AE-hit for 1-2 sensor's group location. b) ratio between cumulative AE-event and cumulative AE-hit. d) Comparison of AE-event energy and AE-hit energy. d) Plot of AE-event energy curve and crack front propagation. Plotted in figure 5 is, for each AE sensor, the cumulative AE-event along with the cumulative AE-hit. Similar results was observed between 1-2 sensor's group location and 3-4 sensor's group location, and only data from the first group are plotted. For linear location mode of AE source, calculation of x-position of each event is based on the measurement of the differences in first wave arrival times between two recorded AE-waveforms (Hits). The first wave arrival time is detected as the first threshold crossing by AE signal. Another parameter necessary for time difference location method is effective velocity. It can be established experimentally with or without considering different wave propagation modes (longitudinal, shear and Rayleigh waves). In this study, the value of effective AE wave velocity was evaluated by the conventional pencil lead breaking, and the obtained value is 5350m/s. The propagation modes were not separated inducing AE-hits which cannot be located. Indeed, figures 5.a&b show that approximately 30% of the average recorded hits from the 1-2 sensor's group location are located. However, figure 5.c shows a good correlation between AE-event energy and AE-hit energy. It should be noted that AE-hit energy is not corrected according to the attenuation curve. Some part of the no-located events can be caused by external noise such that caused by the loading system. Finally, if we compare figures 4.d and 5.d it can be shown that greater correlation between the energy release and the crack front propagation is obtained
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