Granular Material Characterisation at the Macroscopic Scale for the Validation and the Calibration of Numerical Models

Numerical simulation is a useful tool for studying the behaviour of powders. Nowadays, very computing efficient DEM codes are available and allows to simulate powder processes at large scale. However, finding suitable values for the microscopic parameters (coefficients of friction, coefficients of restitution, cohesive interactions, ...) to reproduce granular materials behaviour is not trivial, in particular when dealing with real powders made of grains having complex characteristics. Moreover, in many simulation techniques, the input parameters are not directly linked with physical characteristics of the particles.

Measurements can be performed at the scale of the grains with AFM techniques for example to obtain a microscopic characterization. Even if this bottom-up method makes sense conceptually, theorical background linking micro model parameters to macroscopic behaviour is still missing.

We propose a top-bottom method based on a macroscopic characterization workflow composed of three measurements: the packing fraction dynamics (GranuPack [1]), the flowability and cohesiveness (GranuDrum [1]) and the ability of the powder to create electrostatic charges during a flow (GranuCharge [2]). These measurements are performed in well-known geometries (tubes or rotating drum) and thus can be easily simulated. Therefore, the experimental results can be directly compared with the simulations to make a validation of the selected parameters. After a description of the measurement workflow, case studies are presented.