Avalanches during sea snail fracture: Power-law mixing in layered composite materials

Layered composite materials are common in fields such as integrated circuits, aircraft, and biomedicine. Here, we study the avalanche-like failure mechanism of the shell of Peristernia reincarnate, a typical marine gastropod mollusk with an alternating soft and hard layered composite structure, through the analysis of acoustic emission signals. Unlike the widely studied seismic activities and failure of common porous materials, the energy release distribution of this layered composite material does not show a single power-law distribution but rather a mixture of two different power-law damage mechanisms. The horizontal asymptotes of the maximum likelihood estimation curve of the critical exponent correspond to different power-law exponents, among which the higher power-law exponent cannot be obtained by the conventional histogram estimation. We also point out that the effective critical exponent, which was adopted for the atypical pure power-law distribution in previous related studies, is actually the superposition result of different power laws. The power-law mixing occurs throughout the stage of the shell's failure under force, and this mixing is due to the inhibitory effect of the shell's own alternating soft and hard layered composite structure on the development of microcracks into catastrophic cracks that penetrate the structure, allowing the nucleation and initial development of microcracks to coexist for a long time during the compression process. We also examined its waiting time, aftershock decay (Omori's law), and the relationship between the largest aftershock and the main shock (Båth's law).