Predicting failure: acoustic emission of berlinite under compression

Abstract

Acoustic emission has been measured and statistical characteristics analyzed during the stress-induced collapse of porous berlinite, AlPO4, containing up to 50 vol% porosity. Stress collapse occurs in a series of individual events (avalanches), and each avalanche leads to a jerk in sample compression with corresponding acoustic emission (AE) signals. The distribution of AE avalanche energies can be approximately described by a power law p(E)dE = E(-ε)dE (ε ~ 1.8) over a large stress interval. We observed several collapse mechanisms whereby less porous minerals show the superposition of independent jerks, which were not related to the major collapse at the failure stress. In highly porous berlinite (40% and 50%) an increase of energy emission occurred near the failure point. In contrast, the less porous samples did not show such an increase in energy emission. Instead, in the near vicinity of the main failure point they showed a reduction in the energy exponent to ~ 1.4, which is consistent with the value reported for compressed porous systems displaying critical behavior. This suggests that a critical avalanche regime with a lack of precursor events occurs. In this case, all preceding large events were 'false alarms' and unrelated to the main failure event. Our results identify a method to use pico-seismicity detection of foreshocks to warn of mine collapse before the main failure (the collapse) occurs, which can be applied to highly porous materials only.

Avalanches in compressed porousSiO2-based materials

“…Experimentally, it has been shown that the avalanches stem from sudden changes of the internal strain field (displacement discontinuities), which usually lead to shrinking of the sample and can be detected by measuring the acoustic emission (AE) originating from contraction. Avalanche behavior has been observed previously in porous Vycor glass [10], natural goethite [11], porous alumina [12], and berlinite [13]. Their statistical characteristics share many similarities with seismicity such as the Earth crust failure due to stresses originated from plate tectonics [14,15].…”

“…Nevertheless, the corroboration of this hypothesis certainly requires more detailed investigations. The behavior in SiO 2 -porous materials is different from other porous materials such as goethite [11], berlinite [13], or alumina [12], which are also granular materials.…”

Microscopic precursors of failure in soft matter

“…In this context, we mention insightful laboratory experiments on porous rocks using microtomography, which show evidences of nucleation and propagation of precursory deformation and of self-organization of porosity prior to catastrophic failure 10 . Other 'labquake' experiences determined precursors of failure by measuring the acoustic emission of rock samples under compression 11 , finding that in sufficiently porous materials an increase of energy emission occurs near failure. This led to the proposal of using pico-seismicity detection of foreshocks for the prediction of mine collapses in highly porous environments.…”

Predicting sample lifetimes in creep fracture of heterogeneous materials

“…The problem of how to predict material strength and sample failure is where engineering, materials science, and physics meet [1][2][3][4]. The predictability of lifetimes of structures and materials involves phenomena on various scales, beginning with atomic interactions.…”