Speaker
Description
How do soft granular materials (or dense amorphous systems) respond to
externally applied deformations at different rates – from fast to slow
to very slow – and for different system sizes? This long-standing
question was intensively studied for shear deformation modes, but only
more recently also for isotropic deformations, like
compression-decompression cycles [1,2]. For moderate strain rates, in
the solid-like state, above jamming [3,4,5], the system appears to
evolve more or less smoothly in time/strain, whereas for slow enough
deformations, the material flips intermittently between the elastic,
reversible base-state and plastic, dynamic “events”. Only during the
latter events the micro-structure changes, it re-arranges,
irreversibly. The reversible base state involves both affine and
non-affine deformations, while the events are purely non-affine.
Besides their phenomenology and statistical properties, in particular,
the system size and rate dependence [6] of the events is studied,
providing reference data, to be compared in future to experiments on
model materials
like hydrogel particles using modern techniques. Finally, perspectives
and relations to real materials in application are to be addressed.
Figure 1 displays the affine, non-affine, and total displacement
fields, where in the center of the event (much larger localized
displacements) the particles are highlighted.
Figure 2 displays the kinetic to potential energy ratio during
compression from below jamming to above, for various different system
sizes and strain-rates. The zoom-in in Fig. 2 (right) allows to
observe isolated events (for slow enough compression rate) and their
exponential decay of granular temperature (dynamic cooling) relaxing
towards the steady, smooth, elastic situation between events. The
larger the system size, the more events occur, overlapping in time
(strain) if the compression rate is too fast.
References
[1] K. Taghizadeh, S. Luding, R. Basak, L. Kondic, Understanding slow
compression of frictional
granular particles under slow compression by network analysis, Soft
Matter (submitted 2023)
[2] S. Luding, K. Taghizadeh, C. Cheng, L. Kondic, Understanding slow
compression and
decompression of frictionless soft granular matter by network
analysis, Soft Matter 18, 1868 (2022)
[3] S. Luding, Granular matter: so much for the jamming point, Nature
Physics 12, 531-532, 2016
[4] N. Kumar, S. Luding, Memory of jamming -- multiscale models for
soft and granular matter,
Granular Matter 18, 58, 2016
[5] S. Luding, Y. Jiang, and M. Liu, Un-jamming due to energetic
instability: statics to dynamics,
Granular Matter 23, 80, 2021
[6] S. Luding, How does static granular matter re-arrange for
different isotropic strain rate?, in
Powders & Grains 2021 – EPJ Web of Conferences (2021), Vol. 249, p. 10001
[7] S. Luding, Elastic-plastic intermittent re-arrangements of
frictionless, soft granular matter under
very slow isotropic deformations, Frontiers Physics 11, 1211394, 2023
