Experimental evidence of accelerated seismic release without critical failure in acoustic emissions of compressed nanoporous materials

TL;DR

This study investigates acoustic emissions during compression of nanoporous silica materials, revealing multiple accelerated seismic release events without a singular critical failure point, challenging traditional critical failure models.

Contribution

It demonstrates that ASR can occur without a critical point due to dissipation and hardening, providing new insights into failure processes in nanoporous materials.

Findings

Multiple ASR periods observed without critical failure.

AE energy distribution remains stationary despite activity increases.

Critical exponents partly align with mean field models.

Abstract

The total energy of acoustic emission (AE) events in externally stressed materials diverges when approaching macroscopic failure. Numerical and conceptual models explain this accelerated seismic release (ASR) as the approach to a critical point that coincides with ultimate failure. Here, we report ASR during soft uniaxial compression of three silica-based (SiO$_2$) nanoporous materials. Instead of a singular critical point, the distribution of AE energies is stationary and variations in the activity rate are sufficient to explain the presence of multiple periods of ASR leading to distinct brittle failure events. We propose that critical failure is suppressed in the AE statistics by dissipation and transient hardening. Some of the critical exponents estimated from the experiments are compatible with mean field models, while others are still open to interpretation in terms of the solution of frictional and fracture avalanche models.