Executive Summary

One of the long term barriers to particulate modelling of particulates is the lack of suitable test particles that can be used for model validation. This IFPRI project presents a new 3D printing approach to creating test agglomerates with “tunable” properties. Agglomerates were designed using EDEM or CAD software and printed on a polyjet 3D printer. Materials with different mechanical properties were used to print the particles and the inter-particle bonds, allowing combinations of bond strength, particle strength and agglomerate structure to be tested. Quasi-static compression tests (including cyclic loading) and high strain rate impact tests were performed to investigate the breakage behaviour of the printed agglomerates in terms of structure, orientation, bond properties and strain  rates.

Agglomerate deformation and breakage was simulated via Discrete Element Method (DEM) using the Timoshenko Beam Bond Model (TBBM) with bond properties matching the 3D printed agglomerates. For the two main types of agglomerate structures used in this project, the simulation and experiment showed similar qualitative breakage patterns. Mechanical testing of the sub-structures (the polymers using in the printer, and single bond “doublets” tests were performed to characterise the bond stiffness and strength in agglomerates. FEM analysis of doublet compression was performed to identify the elastic limit of the bonds, to be within the validity of the TBBM model. Qualitatively the DEM produced accurate predictions of the macroscopic breakage behaviour, and was able to quantitatively predict the compressive load during the initial deformation of the agglomerate. Although some issues were identified - possible anisotropy of agglomerate strength due to the 3D printed layers depending on the polymer selected, and the non-linear behaviour of the polymers used by Stratasys - these reflect the kind of complexities found in industrial agglomerates, and identifies clear directions for future work.

This IFPRI projects has demonstrated, for the first time, how new 3D printing technology can be used to bring “in silico” particles into the physical environment, to enable rigorous testing of agglomerate deformation  and breakage that has not previously been possible.