Evidence of mechanically activated processes in slow granular flows

Area of Science:

• Physics
• Materials Science
• Rheology

Background:

• Granular materials exhibit complex mechanical behaviors.
• Shear bands are localized zones of intense deformation within these materials.
• The influence of shear bands on distant, non-sheared regions is not fully understood.

Purpose of the Study:

• To investigate how a shear band affects the mechanical response of a granular material in regions away from the band.
• To quantify the changes in intruder motion due to the presence of a shear band.
• To elucidate the underlying physical mechanism governing this altered behavior.

Main Methods:

• Microrheology experiments were conducted using an immersed rod.
• A constant force (F) was applied to the rod positioned outside the shear band.
• The creep velocity (V(creep)) of the rod was measured as a function of applied force and distance to the shear band.

Main Results:

• In the absence of a shear band, a critical force (F(c)) was required to initiate intruder motion.
• The presence of a shear band allowed intruder movement even for forces F < F(c).
• The creep velocity exhibited a dependence on the force difference (F(c) - F) and proximity to the shear band.

Conclusions:

• A shear band significantly modifies the mechanical behavior of granular materials in adjacent non-sheared zones.
• The observed phenomenon can be modeled using an Eyring-like activated process.
• This study provides insights into the non-local effects of localized deformation in soft matter.