Comparing failure tests on pharmaceutical tablets: Interpretation using experimental results and a numerical approach...

Area of Science:

• Pharmaceutical Sciences
• Materials Science
• Mechanical Engineering

Background:

• Mechanical strength is a critical quality attribute for pharmaceutical tablets.
• Standard failure tests like the Brazilian test and three-point bending test are used to determine tensile strength (TS).
• Literature reports conflicting TS values from different tests, often attributed to the maximum stress criterion.

Purpose of the Study:

• To investigate the discrepancies in TS values obtained from different failure tests for pharmaceutical tablets.
• To test the hypothesis that the maximum stress criterion is unsuitable for heterogeneous and quasi-brittle pharmaceutical tablets.
• To implement and calibrate a numerical fracture criterion, the cohesive zone model (CZM), as an alternative.

Main Methods:

• Experimental calibration of the cohesive zone model (CZM) using tablet failure tests.
• Numerical simulations employing the calibrated CZM to predict tablet breaking forces.
• Comparison of numerical results with experimental data and literature findings.

Main Results:

• Numerical breaking forces using the CZM showed good agreement with experimental values.
• The CZM approach successfully captured the trends observed when comparing different failure tests.
• The model reproduced the factor of 2 difference in TS between three-point bending and diametral compression tests found in literature.

Conclusions:

• The maximum stress criterion is inadequate for accurately assessing the tensile strength of pharmaceutical tablets due to stress heterogeneity and their quasi-brittle nature.
• The cohesive zone model (CZM) provides a more suitable numerical approach for evaluating pharmaceutical tablet mechanical strength.
• The CZM can reconcile discrepancies in TS measurements from different testing methods, improving the reliability of tablet mechanical property assessment.