Correlations between electrical and mechanical signals during granular stick-slip events

TL;DR

This study investigates the relationship between electrical signals and mechanical slip events in granular materials, revealing correlations with displacement and acoustic emissions, and highlighting surface charge effects during slip.

Contribution

It provides new quantitative analysis of electrical-mechanical correlations in granular slip events, emphasizing surface charge roles and asymmetries before and after slips.

Findings

Strong correlation between displacement, acoustic emissions, and voltage.

Voltage generation linked to surface properties of granular materials.

Asymmetry observed in pre-slip and post-slip electrical signals.

Abstract

Powders and grains exhibit unpredictable jamming-to-flow transitions that manifest themselves on geophysical scales in catastrophic slip events such as landslides and earthquakes, and on laboratory/industrial scales in profound processing difficulties. Over the past few years, insight into these transitions has been provided by new evidence that slip events may accompanied, or even preceded, by electrical effects. In the present work, we quantify the correlation between slip and the separation of electrical charges, using an archetypal granular material: photoelastic polymers. We measure a strong correlation between material displacement, acoustic emissions, and voltage. We find that the generation of voltage is associated with surface, rather than bulk properties of the granular materials. While voltage precursors are only occasionally observed in this system, there is some asymmetry in the cross-correlation between the slip and voltage signals that indicates differences between the pre-slip and post-slip dynamics.