Criticality indices provided by the evolution of pressure stimulated currents and acoustic emissions in the natural time domain

Abstract

The target of this study is to detect the existence of criticality indices, namely, indices which may be considered as in-time warning signals about the entrance of a mechanically loaded system into its critical stage, i.e., the stage of impending fracture. To achieve this target advantage is taken of the experimental data provided by two sensing techniques, namely the Acoustic Emissions and the Pressure Stimulated Currents ones. The innovation of the present study is that the temporal evolution of the acoustic and electrical activities is implemented in terms of the Natural Time rather than in terms of the conventional time. The experimental protocol included three-point bending tests with centrally notched beam-shaped specimens made of either plain concrete or concrete reinforced with either plastic or metallic short fibers. The comparative analysis of the acoustic and electric activities in the Natural Time Domain revealed that both techniques provide clearly distinguishable criticality indices. Moreover, it was proven that the overall evolution of the acoustic activity is quite compatible with the respective one of the electric activity, concerning both the instant at which the pre-failure indices are detected, and, also, the duration of the respective regions of criticality.