Issue 50

I. Dakanali et alii, Frattura ed Integrità Strutturale, 50 (2019) 370-382; DOI: 10.3221/IGF-ESIS.50.31 376 Differences observed between the curves of all experiments within each class could be well attributed to uncontrollable parameters related to the inhomogeneity and anisotropy of Dionysos marble [19-23], the size effect characterizing its pro- perties [24,25] as well as to the different properties of the paste. The LVDT indications (blue line) for the bar’s movement during the experiments for two characteristic tests of each class are shown in Fig.7. The 1 st and 2 nd class LVDT curves present three distinct inclination changes before the maximum load. The first two changes are due to the elastic response of the whole experimental system and only the third change is due to the bar’s sliding. It is observed that there is a correlation between the load curve and the respective LVDT’s curve. It also seems that the load vs. time curve could be sensitive to the experimental configuration’s boundary conditions and specific specimen details, which leads to variations on the behavior recorded (Fig.7). For example, for 1 st and 2 nd class, three changes of inclination are generally observed but for the second test in 2 nd Class (Fig.7b) there is an initial concave upward LVDT curve followed by a concave downward part. The respective curves of two characteristic push-in tests (Fig.7c) show that the LVDT indications’ rate changes slightly before the maximum load. Data from innovative sensing techniques A thorough analysis of the data gathered from the AE sensors reveals that the acoustic emission recordings are in temporal correlation with the changes of the bar’s displacement and the load. This correlation can be seen in Fig.8, in which the time variation of the duration and energy of the AEs are plotted versus time, in conjunction with the respective time variation of the data gathered from the LVDT in contact with the bar’s lowest end, for a 1 st class typical test. In the same figure, the variation of the load versus time is plotted (green line). It is evident that the AEs before the bar’s sliding are fewer and of lower energy and duration compared to the respective AEs of the 3rd part, after the sliding starts. Figure 8: ‘1 st Class’ test: time variation of the load and the LVDT indications with the duration and energy (contour plot) of the AEs. Figure 9: ‘1 st Class’ tests: variation of the bar’s displacement and cumulative energy of the AE versus load.