Issue 41

S. K. Kourkoulis et alii, Frattura ed Integrità Strutturale, 41 (2017) 536-551; DOI: 10.3221/IGF-ESIS.41.64 546 0 100 200 300 400 1.0 1.5 2.0 2.5 3.0 0 500 1000 1500 Load [kN] Ib [-] Time [s] ib value load 0.5 1.0 1.5 2.0 2.5 3.0 0 5000 10000 15000 20000 25000 0 500 1000 1500 Ib- value RA [μs/V] Time [s] mRA Ib value Ib -value 0.5 1.0 1.5 2.0 2.5 3.0 0.00 0.60 1.20 1.80 2.40 3.00 0 500 1000 1500 Ib -value Energy (PSC) [aA 2 s] Time [s] Energy (PSC) Ib value Energy (PSC) Ib -value n g S b -val Figure 10: Time variation of the Ib -value in juxtaposition to the respective variation of the load imposed load drop caused by the local fracture of the upper corner of one of the two fragments (Fig.4), which results, in fact, to an instantaneous relief of the stress field within the epistyle’s body. After this time instant the load starts increasing again and the Ib -value increases abruptly reaching finally values even exceeding Ib =2.5. Similar behaviour of the Ib-value has been already observed and discussed in refs.[34, 35]. At the time instant at which the Ib-value starts increasing again after its drop at t=1150 s, a similar behaviour is exhibited by the RA parameter. This is clearly seen in Fig.11a, in which the time variation of RA is plotted in juxtaposition to that of the Ib -value: RA is very low, varying in the region 0<RA<5x10 3 μs/V for the time-interval from 0<t <1150 s. Suddenly at t=1150 s the value of RA is skyrocketed exceeding 20x10 3 μs/V, i.e., more than four times higher. Along the same lines the time variation of the Ib -value is considered in comparison to the respective variation of the energy of the PSC [36]. The two plots are shown in Fig.11b. It is revealed from this figure that the energy of the PSC increases more or less smoothly against time for the time interval 0<t<1000 reaching a maximum value equal to about 0.45 aA 2 s. Then it remains almost constant until t=1150 s where it exhibits an explosive increase to a value exceeding 2.50 aA 2 s, i.e., almost five times higher compared to the maximum value attained until the specific time instant. The specific conclusion is of utmost importance since it indicates again a close qualitative correlation between the recordings of the AE and PSC techniques, which could be used in the near future in the direction of quantitatively calibrating the PSC technique as Continuous Structural Healthy Monitoring tool. (a) (b) Figure 11: Time variation of the Ib -value in juxtaposition to the respective variation of (a) the RA parameter and (b) PSC energy.