Issue 40

E. D. Pasiou et alii, Frattura ed Integrità Strutturale, 40 (2017) 41-51; DOI: 10.3221/IGF-ESIS.40.04 48 Figure 5 (con’t) : The energy calculated by both PSC and AE techniques versus the strain energy density for a typical specimen of (b) mortar and (c) glass. As a next step, an effort was made to investigate any correlation which might exist between the quantities E PSC and E AE calculated by the two experimental techniques. In Figs.6(a-c) both energies are presented in logarithmic scale for a typical specimen for each material studied here. The solid dark blue circles represents the period where the electric current produced is very weak without noticeable changes while the empty symbols corresponds to the increase of the PSC until it reaches its maximum value. It is clear that the correlation is much better when the energy emitted increases considerably (empty dark blue circles). Therefore, ignoring the period where PSC is almost constant or increases very smoothly, it was found that the correlation of the energies calculated based on both experimental techniques obeys a power law, i.e.   m PSC AE E E  , where m~0.8 for both marble and glass specimens while m~0.7 for mortar specimens (Figs.6(a-c)). C ONCLUSIONS he correlation of both experimental techniques used in the present experimental protocol is highlighted. More specific, it was found that when the Ib-value decreases, the electric signal detected by the PSC technique starts increasing considerably indicating the formation of cracks. All three materials (marble, mortar and glass) enter a critical state (i.e. Ib-value tends to 1.0) when strain is equal to about 65-75% of the maximum strain (stress level equals to about 95% for marble, about 75% for mortar and about 65% for glass). The same stress level, at which the damage state of Dionysos marble becomes critical, is also obtained by other researchers based on the variation of the b-value [35]. The alternative approach which was based on the energy released during loading of the specimens, although it makes very T 1E-4 1E-3 1E-2 1E-1 1E+0 1E-3 1E-2 1E-1 1E+0 Energy Strain Energy Density 1E-7 1E-6 1E-5 1E-4 1E-3 1E-2 1E-1 1E+0 1E-5 1E-4 1E-3 1E-2 1E-1 1E+0 Energy Strain Energy Density knee PSC knee AE knee PSC knee AE (b) (c)