Sensitivity of elastic parameters during the numerical simulation of pharmaceutical die compaction process with Drucker-Prager/Cap model

Abstract

Numerical simulation of the die compaction process with Drucker-Prager/Cap (DPC) model is increasingly used to understand the powder behavior during compression. The use of DPC model to numerically simulate the powder compression requires the characterization of a number of parameters like the DPC model parameters, the elastic parameters and the friction coefficient.The methods used to characterize the required parameters are well detailed in the literature. Nevertheless, the values determined for a given parameter of a product varies from a study to another. The effects of the variations of some plastic parameters were already studied in the literature, but the influence of elastic parameters has not been assessed. Then, to investigate such an influence, in this article, we have used already published values for the elastic parameters of microcrystalline cellulose. Moreover, realistic deviations of the values of Young's modulus and Poisson's ratio, based on the differences observed in the literature were introduced in the numerical simulation performed with the Drucker-Prager/Cap (DPC) model and their effects on the results were analyzed.The results show that the variation of the Young's modulus E has no influence on the distribution of the relative density, the axial and radial stresses and on the final tablet thickness. On the other hand, variations of the Poisson's ratio lead to a change of the results of the compaction. The residual radial stresses are low when high Poisson's ratio values are used in the simulation. In particular the residual die wall pressure decreases and tends towards zero when the Poisson's ratio increases. In the case of simultaneous variations of the Young's modulus and the Poisson's ratio, the effects on the numerical results are principally due the change of the Poisson's ratio. Nevertheless, the elastic recovery is more important when the values of the two parameters are low.This work clearly highlights a link between the Poisson's ratio and the residual die wall pressure. Since a correlation was established between the die wall pressure and the occurrence of some defects like capping, it is important to well characterize the Poisson's ratio for a good prediction of capping phenomena when using FEM modeling.