Quantitative evaluation of transient pressure fluctuation behavior in jump tests applied to pharmaceutical powder materials

Abstract

Strain-rate sensitivity in certain metallic materials results from the interplay between two opposing mechanisms: positive strain-rate sensitivity (PSRS), wherein resistance to deformation increases with the strain rate, and negative strain-rate sensitivity (NSRS), which is associated with dynamic strain aging. In our previous study, jump tests on pharmaceutical powders revealed stress transients indicative of NSRS by Desbois et al. (2022) [1].

However, these observations were limited to few powders, and the underlying causes of the transient behavior were not fully explained. Building on these findings, we conducted jump tests on multiple exhibiting a range of viscoplastic behaviors. During the tests, both die wall and punch pressures were simultaneously measured to evaluate the von Mises and hydrostatic stresses. Pronounced transient fluctuations were observed in the von Mises stress, particularly for strongly viscoplastic powder materials. The results indicated contributions from the NSRS and suggested the involvement of a deviatoric stress component. To interpret the transients observed during the jump tests, we applied the two-factor framework proposed by Kaneko and Oyamada (2000) for metals.

Furthermore, a two-factor constitutive model was developed representing PSRS- and NSRS-driven responses to quantitatively assess the balance between the PSRS and NSRS. The model reproduced both the magnitude and timescale of the fluctuations across different materials. Collectively, the results demonstrated that the interplay between the PSRS and NSRS governs the complex stress evolution observed in the jump tests, underscoring that the strain-rate sensitivity of powder materials results from the relationship between the PSRS and NSRS.

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Materials

Six pharmaceutical excipients were employed in all the experiments: lactose monohydrate (GLac) (Excipress, Armor Pharma, Maen Roch, France), anhydrous calcium phosphate (AE) (Anhydrous Encompress, JRS Pharma, Weissenborn, Germany), dihydrate calcium phosphate (D160) (DiCafosD160, Budenheim, Budenheim, Germany), microcrystalline cellulose (MCC) (Vivapur 12, , Rosenberg, Baden-Wurtemberg, Germany), starch (Sta) (Startab, Colorcon, etc.), lactose monohydrate (Lac) (Excipress GR 150).

Yusuke Imayoshi, Shuji Ohsaki, Hideya Nakamura, Satoru Watano, Pierre Tchoreloff, Vincent Mazel, Quantitative evaluation of transient pressure fluctuation behavior in jump tests applied to pharmaceutical powder materials, Powder Technology, Volume 471, 2026, 122105, ISSN 0032-5910, https://doi.org/10.1016/j.powtec.2025.122105.

Read also our introduction article on Microcrystalline Cellulose here: