SPECIFIC FEATURES OF THE ACOUSTIC EMISSION GENERATED BY THE INPACT INDUCED DAMAGE OF UNIAXIALLY COMPRESSED GRANITE
I.P. Shcherbakov1, A.E. Chmel1
1Ioffe Institute, St. Petersburg, Russia
Keywords: granite, combined load, dynamic fracturing, acoustic emission, trigger effect
Abstract
Uniaxially compressed granites were subjected to orthogonally directed pointed impact damaging. The shock-induced acoustic emission (AE) was detected by a highly sensitive wide-band piezo-transducer made of PZT ceramics. The AE time series were analyzed in the frequency ranges of 80–200 кГц (conditionally low-frequency zone) and of 300–500 кГц (high-frequency zone). The energy distributions in AE pulses detected in the lower frequency range followed a power law specific to the cooperative microcracking process, while the distributions recorded in the higher frequency zone exhibited an exponential (Poisson-like) function distinctive to random, non-interacting AE-events. The microcrack accumulation in the low-frequency zone was characterized by the b-value based on the Gutenberg-Richter law. At constant impact energy, the b-value grew progressively with the increase of the uniaxial compression of samples from zero to the highest nondestructive value thus indicating the decrease of the contribution of larger cracks. At the compression close to (but not reaching) the ultimate strength, an impact action caused the subthreshold fragmentation (trigger failure) of granite.
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