Localized Densification during the Stage II–III Transition ‐ Compaction Efficiency at High Pressures

Abstract

Localized densification and compaction efficiency at high pressures was studied using X‐ray computed tomography. Stage III begins with the initiation of a region of uniform average density within the overall high‐density zone. No further densification occurs in this region; additional pressure is transmitted into adjacent, less‐dense zones and the die wall. This localized increase in wall friction continuously decreases compaction efficiency. Discrete element modeling was used to visualize force transfer. The transition was governed by events that ranged from the microscale to the macroscale. Terapascal levels of pressure were required to produce a uniform compact.

Static and dynamic compaction of ceramic powders

“…The stress-density relationship provides no evidence of localization within the compacting sample. However, previous ceramic compaction experiments and modeling (Kong and Lannutti, 2000;Nam and Lannutti, 2004) have shown that non-uniform densities can develop in the specimen, albeit at lower stresses than in the current experiments.…”

Discrete Element Simulations of the Compaction of Aggregated Ceramic Powders

“…Thus, DEM offers a unique tool to introduce pertinent microstructural characteristics into simulations. It is worth noting that the DEM generated compaction curves clearly reproduce the three stages of compaction that are generally observed in aggregated powders 14 . This has been obtained naturally by introducing simple contact laws together with realistic material parameters in the simulations.…”

“…As observed experimentally for many types of aggregated powders, 13,14,32–34 no significant densification takes place in the first part until a certain critical axial stress, σ c , is reached. Comparison of Figs.…”

“…They are mostly involved with metallic 6–9 or composite powders 10–12 . Some of them have treated the compaction of ceramic powders, 13,14 and there have been some recent efforts toward understanding the effect of morphology on granule breakage 15 …”

“…Kong and Lannutti 13 and Nam and Lannutti 14 have already used DEM simulations to model the compaction of such powders. They were able to reproduce the three stages generally observed in the compaction of aggregates, namely aggregate rearrangement (stage I), aggregate fracture (stage II), and primary particle rearrangement (stage III).…”