Transverse compression for the measurement of the tensile strength of pharmaceutical tablets: a reassessment in the case of brittle fracture.

The mechanical strength of pharmaceutical compacts is most often quantified by their tensile strength, a quantity commonly assessed through breaking compacts of different shapes. As the current standard practice of breaking materials compressed into thin cylindrical disc, referred to in this work as the classical Brazilian test (CBT), is known to yield inaccurate results due to improper contact between the compact and the platens compressing it, alternative tests, such as the transversal compression test (TCT) and the flattened Brazilian test (FBT), which use, respectively, cuboid compacts and cylindrical discs with flat parallel ends, have been proposed in the literature. While it has been shown that the FBT consistently yields tensile strength values higher than those determined from the CBT, the comparison between CBT and TCT remains inconclusive. The present work aims to clarify this shortcoming for compacts exhibiting brittle fracture behavior using computational simulations and experimental data. The former approach shows that the predicted stress distributions occurring during TCT and FBT are similar, thus the two tests should give comparable tensile strength results. This trend is confirmed experimentally for two commonly used excipients in pharmaceutical formulations: lactose and mannitol. Specifically, our results show that the FBT- and TCT-derived tabletability for these materials are identical and are consistently higher than that determined from the CBT. These results confirm that tensile strength values obtained from the TCT and CBT cannot be directly compared.