Determination of the Critical Stress Intensity Factor (KIC) of Compacted Pharmaceutical Powders by the Double Torsion Method

Abstract

The critical stress intensity factor KIC has been determined for compacts prepared at different pressures from both Avicel PH101 and sorbitol "Instant', by means of a double torsion method. This method avoids the need for displacement measurement and the introduction of notch into the specimens, both of which present problems with pharmaceutical materials. Measurements of fracture loads for such specimens were reproducible. The values of KIC derived for both materials were found to increase linearly with increase in compaction pressure and linearly with decrease in specimen porosity. Extrapolation of the latter relationship to zero porosity gave values of 1.81 and 0.69 MN m-3/2 for the KIC of Avicel PH101 and sorbitol "Instant', respectively.