title: Theoretical investigations into the influence of the position of a breaking line on the tensile failure of flat, round, bevel-edged tablets using finite element methodology (FEM) and its practical relevance for industrial tablet strength testing.
abstract: Flat, round tablets may have a breaking ("score") line. Pharmacopoeial tablet breaking load tests are diametral in their design, and industrially used breaking load testers often have automatic tablet feeding systems, which position the tablets between the loading platens of the machine with the breaking lines in random orientation to the applied load. The aim of this work was to ascertain the influence of the position of the breaking line in a diametral compression test using finite element methodology (FEM) and to compare the theoretical results with practical findings using commercially produced bevel-edged, scored tablets. Breaking line test positions at an angle of 0°, 22.5°, 45°, 67.5° and 90° relative to the loading plane were studied. FEM results obtained for fully elastic and elasto-plastic tablets were fairly similar, but they highlighted large differences in stress distributions depending on the position of the breaking line. The stress values at failure were predicted to be similar for tablets tested at an angle of 45° or above, whereas at lower test angles the predicted breaking loads were up to three times larger. The stress distributions suggested that not all breaking line angles would result in clean tensile failure. Practical results, however, did not confirm the differences in the predicted breaking loads, but they confirmed differences in the way tablets broke. The results suggest that it is not advisable to convert breaking loads obtained on scored tablets into tablet tensile strength values, and comparisons between different tablets or batches should carefully consider the orientation of the breaking line with respect to the loading plane, as the failure mechanisms appear to vary.
authors.affiliation: University College London, Department of Mechanical Engineering, Torrington Place, London WC1E 7JE, UK. Electronic address: f.podczeck@ucl.ac.uk.
authors.forename: Fridrun
authors.initials: F
authors.lastname: Podczeck
authors.affiliation: University College London, Department of Mechanical Engineering, Torrington Place, London WC1E 7JE, UK.
authors.forename: J Michael
authors.initials: JM
authors.lastname: Newton
authors.affiliation: University College London, Department of Mechanical Engineering, Torrington Place, London WC1E 7JE, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Fromme
mesh_terms: D002626:Chemistry, Pharmaceutical; D020342:Finite Element Analysis; D008962:Models, Theoretical; D012984:Software; D013314:Stress, Mechanical; D013607:Tablets / Q000737:chemistry*; D013678:Technology, Pharmaceutical / Q000379:methods*; D013718:Tensile Strength
chemical_list: D013607:Tablets
keywords: Bevel-edge; Brazilian equation; Breaking line; Diametral compression test; Finite element method (FEM); Tablet tensile failure