Elucidation of the capping mechanism during the high-speed tableting process based on FEM simulation and fracture mechanics analysis

Capping is a phenomenon in which the cap of a tablet separates from the bonding area, thereby presenting a significant problem in tablet production. The compression speed is an important factor that affects the occurrence of capping. Capping is a phenomenon in which the tablet cap separates from the band of the tablet. However, the effect of compression speed on capping has not yet been fully elucidated. In this study, numerical analyses were performed using the finite element method (FEM) with the Drucker-Prager cap and Perzyna models at 40 mm/s to further understand the effect of compression speed on capping occurrence. The calculated loading curves agreed with the experimental curves at different tableting speeds. Moreover, the simulation results confirmed that the stress distribution inside the tablet became more non-uniform with increased compression speed. Additionally, we aimed to develop a prediction method for capping tendency using FEM simulation. Predicting the capping tendency by comparing the residual stress and tablet strength at the edge of the tablet is challenging. On the other hand, accurate predictions were achieved by comparing the stress intensity factor with the fracture toughness of the tablets, based on fracture mechanics principles. Our concept of predicting capping tendencies offers valuable insights for advancing research on the tableting process.