Breaking pharmaceutical tablets with a hole: Reevaluation of the stress concentration factor and influence of the hole size
July 15, 2017, midnight
J. B. Kopp
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The mechanical strength of pharmaceutical tablets holds significant importance, and its examination using the principles of linear elastic fracture mechanics has been introduced in the pharmaceutical realm through the Brittle Fracture Index (BFI). This index relies on the stress concentration factor (SCF), and conflicting findings regarding the SCF value during the diametral compression of a disc with a hole have been documented in pharmaceutical literature. In this study, utilizing numerical simulations (FEM) and analytical outcomes, the SCF value was validated to be 6. This result was also found to be applicable to the flattened disc geometry introduced in a prior study. The SCF value was observed to be nearly independent of the hole size when the ratio between the hole and tablet diameters was below 0.1. However, experimental findings presented in this paper demonstrate that the load required to break a compact varies with the hole size. This influence stems from alterations in the stress distribution around the hole as its size changes. Criteria such as the average stress criterion, accounting for stress distribution, helped elucidate the impact of the hole on the breaking load.