granulares

Granulares, in the context of physics and materials science, refers to granular materials, which are ensembles of macroscopic particles that interact primarily through contact forces. Examples include sand, grains, powders, and pellets. These materials are distinct from fluids or crystalline solids because their behavior is dominated by grain-to-grain interactions, friction, and inelastic collisions rather than thermal agitation.

Granular systems are often treated as athermal: temperature plays a negligible role in their macroscopic dynamics, while external energy input from shaking, stirring, or shearing sustains motion. They exhibit a range of behaviors from solid-like to fluid-like, and even gas-like under strong agitation. When at rest, they can jam and sustain shear stresses; when sheared, they flow with complex constitutive relations. Key properties include packing fraction, angle of repose, and force chains, which are networks of contacting grains that carry stresses within the material. Moisture, cohesion, particle shape, and size distribution strongly influence stability and flow.

Modeling approaches combine discrete and continuum descriptions. The discrete element method (DEM) simulates individual grains and their contacts, while continuum models use averaged quantities such as density and stress to describe bulk flow. Concepts like granular temperature quantify random grain motions, even though the system is not in thermodynamic equilibrium. Phenomena such as size-based segregation (the Brazil nut effect), avalanches on piles, and dilatancy under shear are characteristic of granular media.

Applications span civil engineering (soil behavior, embankments), pharmaceuticals and food processing (powder handling), and industrial processing (granular flows, mixing, and packing). Challenges include predicting non-equilibrium dynamics, jamming transitions, and scale-dependent behavior in complex mixtures.