Issue 41

S. K. Kourkoulis et alii, Frattura ed Integrità Strutturale, 41 (2017) 536-551; DOI: 10.3221/IGF-ESIS.41.64 547 0 50 100 150 200 250 0 3000 6000 9000 12000 Average frequency [kHz] RA [μs/ V] ch01: 0-350s ch01: 351s-950s ch01: 951s-1150s cho1: 1151s-1297s 0 50 100 150 200 250 0 1000 2000 3000 4000 5000 Average frequency [kHz] RA [μs/V] A Β C D 0 100 200 300 400 0 500 1000 1500 Hits/s Time [s] Ch01 T HE SUCCESSION OF FAILURE MECHANISMS n an effort to enlighten the failure mechanisms activated during the loading process of the restored epistyle the approach of considering the relation between the average frequency of the acoustic signals and their RA (rise time per amplitude) parameter, is adopted [16, 17]. The whole duration of the experiment was divided into four intervals according to the time evolution of hits/s which is shown in Fig.12. It is observed that during the first interval the number of hits per second is very small indicating negligible acoustic activity. During the second interval their number is considerably higher (exceeding fifty hits per second) with a smooth increasing tendency. During the third interval the number of hits per second attains huge values even exceeding three hundreds. Finally at the last interval the acoustic activity is again very low. It is worth mentioning that these intervals correspond with good accuracy to the time instants at which the plots of both the deflection and the opening of the fault against time exhibit characteristic slope changes, mentioned in previous sections. The average frequency of the acoustic signals is plotted versus RA in Fig.13a for the as above four time-intervals. Figure 12: The time variation of the hits/s and the time intervals considered (a) (b) Figure 13: (a) The variation of the average frequency of the acoustic signals against the respective RA for the four time intervals considered; (b) The variation of the average frequency of the acoustic signals against the respective RA for a typical pull-out test [11], for four time intervals (A is the first and D the last one) [11]. I P