PSI - Issue 55

Dimos Triantis et al. / Procedia Structural Integrity 55 (2024) 185–192 Triantis et al. / Structural Integrity Procedia 00 (2023) 000 – 000

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while the load tends to attain its maximum value, the average energy exhibits a relatively sudden increase and then it tends to be stabilized within a rather narrow interval forming a kind of a plateau, which is terminated some tenths of a second before the fracture of the specimen tested. Similar qualitative conclusions were drawn for the case of a structural test, namely an experiment during which a copy of a fractured and restored marble epistyle was tested under ten-point bending. In spite of the differences and the much more complex nature of the specific specimen (compared to the wide marble plates and the prismatic marble beams tested in tension and compression, respectively) the average energy content of the acoustic events exhibited a compatible behaviour to that of the elementary experiments. Indeed, at the critical time instant (corresponding now to the slope change of the load-time plot rather than to the maximum load) a plateau of the temporal evolution of the average energy was formed (after a relatively rapid increase), which was terminated at the instant of a second load time slope change (designating activation of an additional damage mechanism). The temporal evolution of the average energy of the acoustic events recorded in the epistyle was studied in juxtaposition to that of the Pressure Stimulated Currents. Remarkable similarities were highlighted, validating somehow the conclusions drawn. Recapitulating it can be stated that the onset of the plateau of the average energy constant may be well considered as a relatively early signal, warning about upcoming entrance of a system into its critical stage. 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