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

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  • Otoguro Saori
    Department of Pharmaceutics, Hoshi University
  • Hayashi Yoshihiro
    Department of Pharmaceutical Technology, Graduate School of Medicine and Pharmaceutical Science for Research, University of Toyama
  • Miura Takahiro
    Mechanical CAE Division, Cybernet Systems Company, Ltd.: Tokyo 101–0022, Japan
  • Uehara Naoto
    Department of Pharmaceutics, Hoshi University
  • Utsumi Shunichi
    Department of Pharmaceutics, Hoshi University
  • Onuki Yoshinori
    Department of Pharmaceutical Technology, Graduate School of Medicine and Pharmaceutical Science for Research, University of Toyama
  • Obata Yasuko
    Department of Pharmaceutics, Hoshi University
  • Takayama Kozo
    Department of Pharmaceutics, Hoshi University

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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.

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