We have determined the acoustic and microwave frequencies of a misaligned spherical resonator maintained near the temperature of the triple point of water and filled with helium with carefully characterized molar mass M = (4.002 6032 ± 0.000 0015) g mol

The damage process in a concrete specimen subjected to uniaxial compression test is investigated by detection of the propagating elastic waves because of micro-and macrocrack growth. Besides the high-frequency acoustic emissions (AEs), the presence of low-frequency elastic emissions (ELEs), from 1 to 10 kHz, is detected just before the specimen failure. A spectral analysis of the ELEs is performed by measuring with a calibrated transducer the local acceleration of the specimen surface. Quantitative information about the macrocrack effects in terms of released energy is thus obtained. Furthermore, the evolution of damage is followed through the analysis of the amplitude distribution of AE and ELE signals, distributed according to the Gutenberg-Richter (GR) statistics.KEY WORDS: acoustic emissions, b-value analysis, elastic emissions, fracture precursors, lowfrequency Ó

We subjected the time series of quasi-rigid-body vibration pulses (elastic emissions) from laboratory fracture carried out by a piezoelectric accelerometer on concrete and rock specimens under uniaxial compression to statistical analysis. In both cases, we find that the waiting-time distribution can be described by a scaling law extending over several orders of magnitude. This law is indistinguishable from a universal scaling law recently proposed for the waiting-time distributions of acoustic emissions in heterogeneous materials and earthquakes, suggesting its general validity for fracture processes independent of modes and magnitude scales.

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