Time correlation of crack formation during impact fracture of rocks

Abstract

Abstract Samples of marble and granite with different grain sizes were subjected to impact fracturing under laboratory conditions. The acoustic-emission (AE) signals generated by growing cracks were detected at 10-ns intervals. Synchronically, the fractoluminescence (FL) resulting from the breakage of interatomic bonds on the sample surface was recorded. The duration of the intervals between the AE signals was shown to be a power-law function, typical of correlated (self-similar) processes. However, the FL signals did not follow this law, because the duration of free-radical formation is much shorter than the intervals at which they appear when chemical bonds break down. The AE data indicate that new cracks appear more often in materials with a smaller grain size.