Abstract
In any DEM simulation, the chosen particle shape will greatly influence the simulated material behaviour. For a specific material, e.g. railway ballast, it remains an open question how to model the particle shape, such that DEM simulations are computationally efficient and simulation results are in good accordance with measurements. While DEM shape modelling for railway ballast is well addressed in the literature, approaches mainly aim at approximating the stones’ actual shape, resulting in rather complex and thus inefficient particle shapes. In contrast, very simple DEM shapes will be constructed, clumps of three spheres, which aim to approximate shape descriptors of the considered ballast material. In DEM simulations of the packing behaviour, a set of clump shapes is identified, which can pack at porosities observed at track sites, as well as in lab tests. The relation between particle shape (descriptors) and obtained packing (characteristic) is investigated in a correlation analysis. The simulated packing’s porosity is strongly correlated to four shape descriptors, which are also strongly correlated among each other. Thus, to derive simple shape models of a given particle shape, matching one of these shape descriptors, might be a good first step to bring simulated porosities closer to measured ones. The conducted correlation analysis also shows that packing’s coordination number and isotropic fabric are correlated to more shape descriptors, making it more difficult to estimate the effect of particle shape on these quantities.Graphic abstract
Highlights
In Discrete Element Method (DEM) simulations, the choice of particle shape and size, the applied contact model with its material parameters and the packing preparation method will determine the simulated bulk behaviour of the material
When a specific material is considered, it is a challenge to separate the influence of particle shape and material parameters
While the angularity of railway ballast is well addressed in the literature, the stones’ nonconvexity is rarely mentioned or quantified
Summary
In Discrete Element Method (DEM) simulations, the choice of particle shape and size, the applied contact model with its material parameters and the packing preparation method will determine the simulated bulk behaviour of the material. The stones under investigation were composed of sharp corners and edges as well as rounded areas and their angularity was analysed. Another important shape characteristic of ballast stones is their nonconvexity, which was evaluated in [51] using the convexity index. Both sharp corners and edges as well as non-convex shapes can be expected to significantly influence the ballast bulk behaviour as they yield a big interlocking potential. Particle shape analysis in general is usually conducted on three different scales: form, angularity/roundness and texture. Roundness was firstly defined by Wadell, [57,58,59], and other definitions exist, see [4] for 2D data or [5, 32, 33, 62, 64]
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