Competition between random and correlated accumulation of primary damages in impact-loaded SiC ceramics

Samples of SiC ceramics differing in porosity in the range 1–9% were damaged by a falling weight, and the fractoluminescence (FL) activity lasting up to 0.4 ms was detected with the time resolution of 10 ns. The recorded time series of the light emission were used for constructing the distributions of the energy release in FL pulses and the time intervals between pulses. The energy release in damage events evolved from a self-similar (power law) distribution in low porous ceramics to a fully random (exponential) distribution in more porous samples. The sequence of time intervals between FL pulses exhibited an opposite trend as transforming from the fully random set of “waiting times” in lower porous ceramics into the self-similar time distribution in the most porous ceramics. These changes in the mechanical behavior of tested ceramics were explained by the formation of the oxidized film on the pore surface and by the increasing structural role of bridges between sintered particles in more porous ceramics, which serve as stress concentrators.