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.
Highlights
The mechanical response of brittle heterogeneous materials under compressive loading and the damage accumulation within their mass, which unavoidably accompanies the loading procedure, are of great interest in a wide range of engineering applications
The acoustic activity was analyzed in terms of the improved b-value (Ib-value) and the cumulative energy of the acoustic signals
As far as it concerns the cumulative energy of the acoustic signals, it was observed that during the stages of constant stress level, its time evolution is governed by a power law with two distinct branches
Summary
The mechanical response of brittle heterogeneous materials under compressive loading and the damage accumulation within their mass, which unavoidably accompanies the loading procedure, are of great interest in a wide range of engineering applications. Plotting Eq(2) on log-log scales (Fig.5a) indicates that the time evolution of the cumulative energy (CE) of the acoustic signals during the constant stress stage B consists, of two distinct branches of different values of the exponent m.
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