(788g) Use and Misuse of the Diametrical Compression Test

The diametrical compression (DC) test has been used extensively to derive the tensile strength of pharmaceutical tablets from the measured breaking force. DC-derived tensile strengths provide a good approach to measuring lot-to-lot variability in the mechanical properties of tablets. For these quality control type applications, method precision is required, but accuracy is not.
Additionally, DC has been used to calibrate parameters of the Druker Prager Cap (DPC) model, a yield criterion expressing the failure of a powder compact under arbitrary 3D loading conditions. For this application, the DC method must not only provide suitable precision, but also accuracy. In this work we explore the accuracy of the DC method in the measurement of tensile strength and conclude that the true tensile strength of a powder compact is approximately double the DC-derived value. While historical literature assumes that tablets fracture under tension along the centerline of the tablet, analysis of the stress state suggests that tablets are likely to fracture under shear. The impact of this ~50% error should be considered when accuracy of the tensile strength result is required.