Seismic instruments: article

Аnnotation: The spectra of acoustic signals obtained during uniaxial compression of artificial sandstone samples under continuous loading through post-ultimate state up to failure, were analyzed. In the present work, we make an attempt to reveal a shift towards the lower values in the characteristic acoustic signal frequency when the load approaches the critical load state. The experiments were performed on the lever press in two modes: simple continuous loading and continuous loading with periodic impact on the sample by the direct current. This was done in order to testify the effect of electric current on the parameters of acoustic emission. In both cases, upon reaching the load close to ultimate and post-ultimate states, the amplitude of the signals in the frequency range of 10–20 kHz begins to noticeably exceed the amplitude of the signals in the frequency ranges above 20 kHz. At the final stage, immediately before the beginning of the avalanche-like rise of acoustic emission activity, an increase in signals with frequencies within the range of 5–10 kHz is marked as well. On the base of identical behavior of the samples, we conclude that the electrical impact did not significantly affect the spectral acoustic signal characteristics. The shift of the frequency interval, which is accounted for the maximum RMS ampli-tudes of the acoustic signal, towards low frequencies may indicate either the formation of larger cracks or the appearance of additional cracks of a different mode than at lower loads (for example, shear cracks). By itself, this phenomenon may indicate impending macro-destruction.