PSI - Issue 3

S.K. Kourkoulis et al. / Procedia Structural Integrity 3 (2017) 326–333 8 S.K. Kourkoulis, D. Triantis, I. Stavrakas, E.D. Pasiou and I. Dakanali / Structural Integrity Procedia 00 (2017) 000–000

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The results of the PSC technique were along the same direction. The electric current recorded is very low and almost linearly increasing up to about 92% of the maximum load attained. Then it starts increasing very abruptly, in dicating entrance to non-steady state and impending catastrophic failure. Similarly, the acoustic activity becomes more intense at load-levels equal to about 95% of the respective maximum value. In addition, the AE technique permitted not only temporal but also spatial monitoring of the damage evolution process. Therefore, it was possible to “guess” the notch from which fracture is to start. The specific “guess” was verified by the data of the ultra high speed camera. This “guess” was also, in agreement with the respective “prediction” of the DIC technique, the results of which were, in turn, in excellent agreement with those of the clip-gauges concerning the NMOD. Recapitulating, it can be safely concluded that the system studied (marble DENT specimens under monotonic uni axial tensile load) enters its critical state at load levels equal to about 90% to 95% of the final fracture load. The pre dictions concerning this critical threshold, as they are obtained from all techniques considered here, differ ony slightly (less than 5%) from each other. Taking into account the inherrent inhomogeneity of marble, these differences can be considered well within the range of accepted experimental error. The results of the present protocol concerning the capacity of the specific sensing techniques to provide pre-failure indicators are in very good accordance to similar ones, drawn from experimental protocols with different materials and loading schemes (Dakanali et al. 2016, Dakanali 2017, Triantis et al. 2015, Kourkoulis et al. 2017). Therefore the potential of AE and PSC techniques to be used for Structural Health Monitoring are further supported, since they provide clear warning signs about upcoming failures. References Dakanali, I., Stavrakas, I., Triantis, D., Kourkoulis, S.K., 2016. Pull-out of threaded reinforcing bars from marble blocks. Procedia Structural Integrity 2, 2865–2872. Dakanali, I., 2017. Applying innovative experimental techniques for the study of the mechanical behavior of structural members of ancient monuments and numerical simulation. PhD Thesis, Supervisor: Kourkoulis, S.K., National Technical University of Athens, Greece. Filippi, S., Lazzarin, P., 2004. Distributions of the elastic principal stress due to notches in finite size plates and rounded bars uniaxially loaded. International Journal of Fatigue 26, 377-391. Inglis, C.E., 1913. Stresses in a plate due to the presence of cracks and sharp corners. Proceedings of the Institute of Naval Architects 55(1), 219-230. Kirsch, G.,1898. 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