Comparative assessment of the acoustic activity and the Pressure Stimulated Voltage in marble specimens under compression

The temporal evolution of the electric activity generated in marble specimens under uniaxial compression is analyzed and quantified in terms of the Pressure Stimulated Voltage (Electric Potential) developed. The evolution of the electric activity is considered in juxtaposition to that of the respective acoustic one, quantified either in terms of the average frequency of generation of acoustic signals or of their Cumulative Energy content. Two classes of specimens were tested, differing with respect to the loading rate imposed. It is concluded that the electric activity is very weak, or even negligible, until the critical instant designated by the entrance into the stage of thermodynamically irreversible response of the material. Beyond this instant the electric activity starts increasing very rapidly almost until the instant at which the load attains its peak value. A few seconds before fracture, the electric signal exhibits an abrupt drop. The temporal evolution of the electric activity and that of the acoustic one are in excellent agreement, independently of the parameter used for their quantification. The study revealed that both activities provide clear pre-failure indices, early warning about upcoming disastrous fracture. Moreover, it was highlighted that the loading rate diversifies the results only from a quantitative point of view, “translating” the stress interval within which the pre-failure indices are located: The higher the loading rate the lower the stress level at which the pre-failure indices are detected.