One of the long term barriers in understanding granule breakage is the lack of a universally accepted test method or test granules to systematically evaluate agglomerate breakage propensity and mechanism. Computer simulations are often used but are limited by the lack of identical, controlled agglomerates to test and validate simple models, let alone replicate the complex structure of real industrial agglomerates.
This report summarises progress to date on a new 3D printing production method of test agglomerates with defined and "tuneable" properties. Agglomerates were designed using Solidworks 2014 software and printed by an Objet500 Connex 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. Compression and impact tests were performed to investigate the breakage behaviour of printed agglomerates in terms of agglomerate orientations, bond properties and strain rates.
The compression and impact results reveal different agglomerate breakage characteristics. For compression tests under low strain rate, breakage occurs at the bond between primary particles, and the compressive strength is influenced by the bond strength significantly. In future, it is worth to further relate the microscopic particle-particle and particle-bond interactions to the macroscopic compressive strength. For impact tests with high strain rate, the agglomerates with flexible bond show rebound behaviour, while the agglomerates with rigid bond fracture. Under the same impact conditions, the rubber materials have high fracture toughness and the rigid materials behave in a more brittle manner that can fracture easily. For the fractured agglomerates, clear fracture planes can be observed with low impact energy. At high impact energy, a large amount of small debris occurs, and the breakage extent increases accordingly.
Now that proof of principle for the approach has been established, the next stage of the project is to conduct systematic studies of agglomerate strengths varying structure, material properties, under various breakage forces, orientations and strain rates.