Excitation of acoustic emission by elastic impulses

Experiments on the deformation of models made of granite debris, quartz san d, and cement were carried out under conditions of biaxial compression at a constant strain rate of epsilon' = 0.26 X 10(-6). The models contained an inner weakened layer, the deformation in which led to fracturing accompanie d by acoustic emission, whose intensity was recorded. The models were perio dically subjected to the action of elastic impulses created by small balls falling front a given height. The following regular features were revealed. This action initiates acoustic events such that the decay of the excited a coustic activity can be described by a power law. The duration of the excit ation phase increases with the impact force or with the repeated impacts. T he fraction of weaker acoustic signals decreases, as the macroscopic fractu re of the sample develops. This phenomenon is an analogue of a decrease in the slope of the recurrence plot, observed in seismological practice at the preparation state of a strong earthquake.