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Abstract
Powder compaction is a fundamental method for size-enlargement, which is widely applied in many industrial fields. The mechanical strength of a compact is a critical property, which is strongly affected by particle property and compaction process. Thus, better understanding of compact strength under different compaction conditions is of great importance to both fundamental understanding and optimization of engineering practice.
This work was to develop a numerical model based on the finite element method (FEM) to investigate powder compaction. The Drucker-Prager Cap (DPC) constitutive equations were adopted in the model. Experiments were also conducted to obtain the values of the parameters in the model. The model was firstly developed to simulate the die compaction of iron ore powders. Low density area was observed at the lower corner where compacts tend to be damaged during handling and transport. During the unloading stage, there was a higher shear stress area located from the top edge to the centre, which is the reason for the capping phenomenon.
The model was then coupled with a nonlinear crack model to predict the compact tensile strength through diametrical compression. The effect of compact shape was also investigated. The stress analysis showed there was a higher shear stress area located from top edge to the centre during unloading. With increasing curvature of compact surface, the responses of the compacts changed from brittle to ductile. The predicted bulk loading response was in a good agreement with experimental results in terms of hardening and softening stress-strain responses. The strength decreased as the friction coefficient increased. However, the failure mode did not vary with friction condition
The FEM model was then applied to modelling a continuous briquetting of powders. Detailed analysis was carried out to show the material flow behaviour and failure pattern inside the pellets. The cause of crack formation was investigated. A parametric study further demonstrated that material properties and operational conditions all contributed to the bulk behaviour of the formed pellets. The output unit was influenced by friction coefficient and input pressure.