Granular rheology · DEM simulation
A Single Dislocation Weakens a Granular Crystal
Main claim
A single edge dislocation glides through a low-friction granular crystal, lowering its yield stress far below that of a defect-free crystal. Even an ordered assembly of grains can become much easier to deform when it contains one line-like structural defect.
Problem
Atomic crystals yield through the motion of dislocations, allowing plastic deformation far below the theoretical strength of a perfect lattice. Granular materials are macroscopic, dissipative, and frictional, so it was not clear whether the same defect mechanism could survive or whether friction would destroy crystalline order before a dislocation could move.
Approach
We constructed a two-dimensional hexagonal granular crystal containing one edge dislocation and sheared it slowly in discrete element method simulations. Interparticle friction was varied systematically. Particle trajectories, local coordination, shear stress, and yield stress were compared across gliding, intermittent, and crystal-breaking regimes and against a defect-free crystal.
What we found
At low friction, roughly below 0.1 in the studied model, the dislocation core moves through the lattice in an inchworm-like sequence and produces plastic deformation. At higher friction, glide is suppressed and crystalline order deteriorates instead. When glide occurs, the yield stress is far lower than for a perfect crystal and varies approximately linearly with friction on top of an elastic Peierls barrier.
Why it matters
The work demonstrates a direct connection between granular rheology and dislocation theory developed for atomic solids. It identifies a defect-enabled route to weakening ordered granular structures and suggests that controlling interparticle friction could tune strength through a mechanism different from conventional lubrication.
Keywords
granular rheology, dislocation glide, DEM simulation, yield stress, Peierls stress.
Paper
, “Dislocation Glides in Granular Media,” Physical Review Letters 135, 048202 (2025).