31 Acoustic Emission Monitoring of Rock Specimens During Fatigue Tests 243 Phase 1 Phase 2 Phase 3 Fig. 31.3 Total Cumulated AE for the specimen made of Etna basalt 100 5000 10000 15000 20000 25000 30000 35000 500 100 80 60 40 20 20 15 10 5 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 3.0 2.0 1.0 0 1000 1500 2000 2500 3000 3500 200 300 400 500 600 700 800 100 200 300 400 500 600 700 800 100 200 300 400 500 600 700 800 100 200 300 400 500 600 700 800 100 200 300 400 500 600 700 800 100 200 300 400 t (minutes) b-value A (mV) f (kHz) AE/min cum AE bt 500 600 700 800 a b c d e f Fig. 31.4 Basalt specimen: First phase. Cumulated AE (a), AE/minutes (b), AE signal Frequency (c), AE Amplitudes (d), “t exponent (e), b-value (f) In Fig. 31.4 the AE analysis are reported in details for the first phase. It is possible to observe an increasing of the AE cumulate number after 10 min from the beginning of the test. In correspondence of this increment in AE activity significant values in the AE/minutes were observed. This value, in particular, reached a peak value of 1,500 hits/min. During this time interval, between 110 and 120 from the beginning of the test the AE are characterized by a frequency range between 20 and 100 kHz. At the same time also the AE amplitudes increased up to 30 mV.
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