Modelling Pasty Material Behaviour Using the Discrete Element Method

Mixtures of a fine-grained dry solid and a liquid, with a higher solid content in the mixture, show paste-like behaviour. In many technical processes, pasty materials are handled in large quantities. Pasty Materials show the same characteristics as Bingham Plastics, behaving like a rigid body but flowing like a viscous fluid under a certain stress level. This behaviour is due to attracting forces between the particles, resulting from the capillary pressure and the surface tension of the liquid, which forms individual capillary bridges or capillary bridge clusters between the solid particles. The behaviour of granular material can be represented in a discrete element method (DEM) simulation. The calibration of the simulation parameters is achieved by comparing laboratory tests, which reflect a typical material characteristic, with the results of calibration simulations. In this project, several DEM contact models, describing attractive forces between particles depending on the distance between them, were analysed and assessed based on their ability to display the pasty material behaviour of a fine-grained solid water mixture with a high water content by comparing the simulation results to a slump test. The most promising contact model was then optimised to enable a minimal computing time for the simulation of bigger technical processes. Many existing contact models also consider attractive forces between particles (e.g. JKR cohesion) but are based on different physical effects. For this reason, the contact models assessed in the course of this project are, in general, based on the capillary effect.