Granular crystal · Lattice spacing

Particle Spacing Controls Dislocation Glide

Main claim

Denser granular crystals sustain dislocation glide up to higher interparticle friction, while their yield stress scales with normal stress over an intermediate-friction regime. Changing the distance between neighbouring grains changes whether a crystal defect can move or the ordered structure breaks.

Granular-crystal simulation representing dislocation glide at controlled particle spacing — Representative image from the granular-dislocation research theme.

Problem

Once dislocation glide was found in a granular crystal, the next question was how robust it is to packing geometry. Lattice spacing changes particle overlap, normal stress, and the width of the dislocation core at the same time. Its interaction with friction therefore determines whether a defect can glide or the crystal loses order.

Approach

Using discrete element method simulations, we prepared monolayered granular crystals with one dislocation and varied both the lattice parameter and interparticle friction. Under slow shear, we tracked the dislocation, crystalline order, yield stress, and normal stress to map the boundary between glide and structural breakdown.

What we found

Denser configurations with smaller lattice spacing preserve dislocation glide up to larger friction coefficients. In the intermediate-friction regime, the yield stress scales linearly with normal stress across the tested lattice parameters. At very small friction, that scaling breaks down because the nearly friction-independent elastic barrier associated with the dislocation becomes dominant.

Why it matters

The study turns the qualitative discovery of granular dislocation glide into a controllable parameter map. Lattice spacing and friction are quantities that can be adjusted in simulations and experiments, so the result helps identify conditions for observing glide and for designing the yield strength of ordered particle assemblies.

Keywords

granular crystal, lattice spacing, dislocation glide, DEM simulation, normal stress.

Paper

Fumiaki Nakai, Takashi Uneyama, Yuto Sasaki, Kiwamu Yoshii, Hiroaki Katsuragi, “Dislocation glides in monolayered granular media: Effect of lattice constant,” EPJ Web of Conferences 340, 04008 (2025).

Published article Open-access preprint