Fracture precursor phenomena in marble specimens under uniaxial compression by means of Acoustic Emission data

Abstract

Marble specimens are subjected to a specially designed stepwise load­­ing protocol, in an attempt to detect fracture precursor phenomena taking advantage of Acoustic Emission (AE) data. The analysis is carried out in terms of the number of acoustic hits recorded and the time evolution of the improved b-value (Ib-value), the cumulative energy of the acoustic signals and the F-fun­c­tion. During the stage of in­creasing load, intense acoustic activity is detected as the cor­responding stress reaches the transitional phase from the linear to the nonlinear mechanical re­sponse of the material. When the stress is stabilized at levels exceeding 95% of the material’s compressive strength, the acous­tic activ­ity is drastically reduced. During the first seconds of the stress stabil­iz­ation stage the reduction follows an exponential law. Special attention is paid to the phases, where the occurrence of AE hits shows a strong increase. During these phases acoustic signals of low frequency and high RA are re­corded, in­di­cating that the micro-cracking process is of shear rather than of opening mode.