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

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.

Stick-slip instabilities in sheared granular flow: The role of friction and acoustic vibrations

“…Stick-slip instabilities are ubiquitous in sheared granular materials ranging from pharmaceutical powders to earthquake fault gouge. Such instabilities are often observed in laboratory experiments [1][2][3][4][5][6][7][8][9]. At much larger scales, these instabilities may explain how aftershocks can be triggered by acoustic waves from earthquakes elsewhere [10][11][12][13][14][15].…”

“…Such instabilities are often observed in laboratory experiments [1][2][3][4][5][6][7][8][9]. At much larger scales, these instabilities may explain how aftershocks can be triggered by acoustic waves from earthquakes elsewhere [10][11][12][13][14][15].…”

Flows and patterns: The physics of fluids, granular materials, and soft matter

“…Bob was reunited with a number of his former Ph.D. students and postdoctoral researchers, colleagues, and former advisors ( This issue features fourteen articles from Bob's former undergraduates, Ph.D. students, and postdoctoral researchers, as well as several collaborators and colleagues. The articles include experimental, computational, and theoretical studies of granular media in microgravity environments [1], vibration-induced avalanches [2], three-dimensional imaging of grain orientations [3], mechanical [4,5] and vibrational [6] response of granular packings, charge interactions during stick-slip behavior [7], variations of flow fields around obstacles [8], hopper flows [9], and compacted powders [10]. In addition to granular materials, the issue also highlights novel studies of colloidal [11] and granular [12] polymers, slurries [13], and transport of sediment by desert beetles [14].…”