Inter-particle adhesion induced strong mechanical memory in a dense granular suspension

Area of Science:

• Materials Science
• Soft Matter Physics
• Rheology

Background:

• Amorphous solids can develop memory of applied strain amplitude through cyclic shearing.
• Previous experiments indicated weak bulk mechanical property changes associated with this memory.
• Yield stress solids, like dense suspensions, are candidates for exhibiting pronounced memory effects.

Purpose of the Study:

• To investigate the memory effect in a yield stress solid (cornstarch in oil) under cyclic shear.
• To quantify the impact of training strain amplitude on memory formation and mechanical properties.
• To elucidate the underlying mechanisms responsible for strong memory encoding.

Main Methods:

• Cyclic shear applied to a dense cornstarch and paraffin oil suspension.
• Measurement of differential shear modulus to quantify memory strength.
• In situ boundary imaging to observe strain localization and particle velocity.
• Varying training strain amplitudes (γT) above and below the yield point.

Main Results:

• The system exhibited training-induced strain stiffening and plasticity, encoding a strong memory of the training amplitude (γT).
• Memory strength decreased with increasing γT, but was observable across a wide range of amplitudes.
• Strain localization occurred at boundaries, with the bulk behaving as a solid plug.
• Particle velocity inside the bulk showed a sudden increase when readout strain exceeded γT.
• Inter-particle adhesive interactions were identified as crucial for the strong memory effect.

Conclusions:

• Dense cornstarch suspensions demonstrate significant memory effects in their mechanical response to cyclic shear.
• Inter-particle adhesion is essential for the observed strong memory, leading to strain stiffening and plasticity.
• The system can retain memory of multiple strain histories, with the most recent smaller amplitude strain being prioritized.