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Towards simulation of compaction processes
* 1 , 2 , 2 , 1 , 3 , 1 , 1
1  Department of Pharmacy, Faculty of Health Sciences, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark
2  Research Center Pharmaceutical Engineering, Inffeldgasse 21 a/II, A-8010 Graz, Austria
3  Danish Fundamental Metrology, Matematiktorvet 307, DK-2800 Kgs. Lyngby, Denmark

Abstract: Tablet compaction consists of several stages and is thus challenging to describe in simple mathematical equations.1 Various numerical approaches have been applied to try and derive a more thorough understanding of the multiple interactions that occur during compaction.2,3 A possible way to obtain insight into the behavior of solids during compression is to perform indentation load – displacememt experiments and simulations4. A finite element modeling (FEM) method utilizing the axisymmetric capabilities of Comsol Multiphysics is presented. The model provides the possibility for evaluating both elastic and plastic deformation occurring during the indentation experiment. This evaluation of the elastic and plastic deformation can be obtained from the calculated load displacement versus pressure profile that provides the maximum indentation depth at the highest load and the final indentation depth after unloading. Elastic recovery can, thus, be characterized by the ratio between the final indentation depth and the maximum indentation depth. The indenter is model as a rigid object that penetrates into the specimen. A mesh is assigned to the entire geometry and a higher mesh density was assigned to the specimen area where the indentation contact occurred. Experimental verification of simulations can be performed using atomic force microscopy (AFM) measurements5,6. It is suggested that data obtained from such indentation load – displacememt experiments are capable of deepening existing understanding of tablet compaction processes 1. Sonnergaard, J. M. A critical evaluation of the Heckel equation. International Journal of Pharmaceutics 1999, 193, 63-71. 2. Wu, C. Y.; Hancock, B. C.; Mills, A.; Bentham, A. C.; Best, S. M.; Elliott, J. A. Numerical and experimental investigation of capping mechanisms during pharmaceutical tablet compaction. Powder Technology 2008, 181, 121-129. 3. Siiria, S. M.; Antikainen, O.; Heinamaki, J.; Yliruusi, J. 3D Simulation of Internal Tablet Strength During Tableting. Aaps Pharmscitech 2011, 12, 593-603. 4. Bolshakov, A.; Pharr, G. M. Influences of pileup on the measurement of mechanical properties by load and depth sensing indentation techniques. Journal of Materials Research 1998, 13, 1049-1058. 5. Garnaes, J. Diameter measurements of polystyrene particles with atomic force microscopy. Measurement Science & Technology 2011, 22. 6. Jee, A. Y.; Lee, M. Comparative analysis on the nanoindentation of polymers using atomic force microscopy. Polymer Testing 2010, 29, 95-99.
Keywords: Simulation, Nanoindentation, Compaction