Modeled effects of density gradients on resonance signatures of pressed powder compacts

Plastic deformation of powder during compaction can cause heterogeneities within the resulting tablet, with models such as the Drucker-Prager Cap (DPC) popular for simulating this process in powder metallurgy and pharmaceuticals. For materials that cannot be homogenized via sintering, persistent density gradients can affect the resulting performance of the tablets but be challenging to quantify in production environments. Prior studies have demonstrated the ability to resolve linear grading with resonant ultrasound spectroscopy (RUS). Here we present work to link 2-D density variations in compressed powder compacts to their resulting modal response characteristics. Using a DPC model calibrated against real-world pressing data, we simulated compaction and relaxation in compacted powders, capturing verticaland radial stress and density gradients arising from plasticity and die-wall friction, with larger-volume tablets exhibiting greater bulk density contrasts. Using the resulting volume distributions, we assess the impacts on the ability of RUS to resolve heterogeneities, highlighting details such as gradient symmetry and mode matching. These results underscore the sensitivity of resonance to subtle density nonuniformities and support the development of RUS-based inspection protocols for detecting process-induced inhomogeneities in compacted powders.