The method of shear cell testing plays a pivotal role in assessing the flowability of powders, notably in the context of evaluating pharmaceutical formulations and processes. Despite numerous studies on shear cell methodology and its diverse applications, there remains a need to compare the performance of specific shear cell designs. This study addresses this gap by offering a comprehensive comparison of two full-bed rotational shear cells – the Peschl and FT4 cells. The evaluation focuses on assessing the precision and accuracy of each instrument, considering six materials: two reference materials with well-established behavior and four pharmaceutically relevant materials. Key parameters obtained from the measured yield loci (including cohesion, unconfined yield strength, flow function coefficient, and angle of internal friction) were analyzed and compared, shedding light on the differences in performance between the two shear cells. Statistical analysis using regression methods revealed the significance of not only the test material but also the shear cell used for measurement, emphasizing the influential role of shear cell design. This work delves into the significance of powder bed density during shear cell measurements and compares the results of the shear cells to orthogonal methods (such as the critical arching diameter and Hausner ratio). Broader implications for comprehensive powder characterization are discussed, providing valuable insights for the field of material science and pharmaceutical formulation.
