Efficient DEM simulations of railway ballast using simple particle shapes

For complex shaped materials, computational efficiency and accuracy of DEM models are usually opposing requirements.
In the literature, DEM models of railway ballast often use very complex and computationally demanding particle shapes in
combination with very simple contact laws. In contrast, this study suggests efficient DEM models for railway ballast using
simple particle shapes together with a contact law including more physical effects. In previous works of the authors, shape
descriptors, calculated in a shape analysis of two types of ballast, were used to construct simple particle shapes (clumps of
three spheres). Using such a shape in DEM simulations of compression and direct shear tests, accurate results were achieved
only when the contact law included additional physical effects e.g. edge breakage. A parametrisation strategy was developed
for this contact law comparing DEM simulations with the measurements. Now, all the constructed simple particle shapes
are parametrised allowing to study their suitability and relating their shape descriptors to those of railway ballast. The most
suitable particle shapes consist of non-overlapping spheres, thus have a high interlocking potential, and have lowest sphericity
and highest convexity values. In a micromechanical analysis of the four best performing shapes, three shapes show similar
behaviour on the bulk and the micro-scale, while one shape differs clearly on the micro-scale. This analysis shows, which
shapes can be expected to produce similar results in DEM simulations of other tests/load cases. The presented approach is
a step towards both efficient and accurate DEM modelling of railway ballast.