Avalanches in compressed porous SiO(2)-based materials.

Area of Science:

• Materials Science
• Geophysics
• Physics

Background:

• Porous silicon dioxide (SiO(2)) materials, including synthetic glass (Gelsil) and natural sandstones, are susceptible to failure under compressive stress.
• Previous studies on synthetic porous SiO(2) glass (Vycor) show similar collapse dynamics.
• Understanding failure mechanisms in these materials is critical for various engineering applications.

Purpose of the Study:

• To investigate the failure dynamics of SiO(2)-based porous materials under slow uniaxial compression.
• To analyze the acoustic emission and sample shrinking during failure events.
• To determine if the failure process exhibits critical behavior and identify statistical properties.

Main Methods:

• Uniaxial compression of Gelsil and three natural sandstones at slow stress rates (0.2–2.8 kPa/s).
• Measurement and analysis of acoustic emission events (energy, duration, waiting times).
• Monitoring sample shrinking during compression-induced jerks.

Main Results:

• Failure dynamics characterized by jerks of strain release and a major collapse, similar to Vycor.
• Acoustic emission data indicate avalanche criticality with power law statistics (exponent ɛ≃ 1.4) over four decades.
• Evidence of aftershock correlations during the failure process, suggesting scale-free behavior.

Conclusions:

• The failure of SiO(2)-based porous materials under compression follows avalanche criticality, consistent with granular media collapse.
• The observed power law statistics and aftershock correlations indicate the absence of characteristic length, energy, and time scales.
• This research provides insights into the fundamental physics governing the failure of brittle porous materials.