Numerical Investigation of the Residual Stress Distribution of Flat-Faced and Convexly Curved Tablets Using the Finite Element Method

Abstract

The stress distribution of tablets after compression was simulated using a finite element method, where the powder was defined by the Drucker-Prager cap model. The effect of tablet shape, identified by the surface curvature, on the residual stress distribution was investigated. In flat-faced tablets, weak positive shear stress remained from the top and bottom die walls toward the center of the tablet. In the case of the convexly curved tablet, strong positive shear stress remained on the upper side and in the intermediate part between the die wall and the center of the tablet. In the case of x-axial stress, negative values were observed for all tablets, suggesting that the x-axial force always acts from the die wall toward the center of the tablet. In the flat tablet, negative x-axial stress remained from the upper edge to the center bottom. The x-axial stress distribution differed between the flat and convexly curved tablets. Weak stress remained in the y-axial direction of the flat tablet, whereas an upward force remained at the center of the convexly curved tablet. By employing multiple linear regression analysis, the mechanical properties of the tablets were predicted accurately as functions of their residual stress distribution. However, the multiple linear regression prediction of the dissolution parameters of acetaminophen, used here as a model drug, was limited, suggesting that the dissolution of active ingredients is not a simple process; further investigation is needed to enable accurate predictions of dissolution parameters. Key words tablet shape; simulation; mathematical model; residual stress; finite element method; multiple linear regression Tablets are the most common and popular dosage form of drug administration. Tablets are generally manufactured by compressing a mixture of dry powders or granules using metal dies and punches. Various stresses remain on the surface and in the interior of tablets after the compression. The effect of the residual stress distributions of tablets on tablet hardenss [1][2][3][4][5][6][7][8] and tableting failures such as capping and lamination 9,10) have been numerically investigated. The finite element method (FEM), in which the powder is modeled using the Drucker-Prager cap (DPC) model, [9][10][11][12][13][14] can be applied to modeling the deformation of pharmaceutical powders 11,15) and thus to simulate the residual stress distribution of tablets. Powders are modeled as continuum media in the FEM and the compaction process is identified by boundary-value analysis. The DPC model is often applied to the analysis of the stress distribution and relative-density changes of the tablets during the tableting process. In examples of the use of the DPC model, Han et al. 12) reported that the density distributions of the tablets were affected by the punch geometry while Wu et al. 9,10) described how tablet failure is more likely to be associated with a band of intensive shear stress generated during the decompression of tablets. Additionally, the density distribution pa...

Latent Structure Analysis of Wet-Granulation Tableting Process Based on Structural Equation Modeling

“…In addition, the deviance information criterion (DIC) is available as another GOF parameter. 25) The DIC is an asymptotic approximation, and it is useful in the model selection problems where the posterior distributions have been obtained by MCMC simulation. The DIC greatly decreased when the early model (Fig.…”

Strength Simulation of Scored Tablets Based on the Finite Element Method Using an Extreme Vertices Design

“…3) Moreover, although the ε 1 was considered as an explaining variable in this study, multivariate analysis-in which all strains of inner tablet are considered as explaining variables-could increase prediction accuracy. 21,22) These approaches might enable us to predict in silico tablet hardness of arbitrary formulation and shape accurately.…”

Finite Element Analysis and Modeling in Pharmaceutical Tableting

“…The largest number of the presented studies (35.6% of the total) deal with the stress/density distribution within the tablet during compression [ 5 , 15 , 27 , 61 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 ]. From these, 31.3% deal with the effect of punch shape [ 61 , 74 , 79 , 82 , 85 ].…”