Molecular Dynamics Simulations of Granular Compaction
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- 作者：Francisco X. Sanchez-Castillo ; Jamshed Anwar ; and David M. Heyes
- 刊名：Chemistry of Materials
- 出版年：2003
- 出版时间：September 9, 2003
- 年：2003
- 卷：15
- 期：18
- 页码：3417 - 3430
- 全文大小：1292K
- 年卷期：v.15,no.18(September 9, 2003)
- ISSN：1520-5002
文摘
We have carried out simulations of the compaction of model granular beds constructedfrom Lennard-Jones (LJ) particles using nonequilibrium molecular dynamics (MD). Thesystems simulated comprised a model die containing either a single granule or many granulesthat were compacted uniaxially by a vertically moving top wall. The simulations whileatomistic in nature can also be considered to have a mesoscopic significance in that theprimary LJ particles represent coarse-grained units that comprise a realistically sizedmacroscopic granule. This representation enables plastic deformation of the individualgranules as well as fusion between granules to be modeled at a fundamental level. As agranule is compressed, the constituent particles move past each other, giving rise to itsdeformation. In a multigranular system, at the points of contact between granules, the surfaceparticles on adjacent granules interact with each other and reproduce many of the featuresof intergranular bonding observed in real systems. The proposed model, although simple,captures the essential physics of the compaction process in a transparent way. It is able toencompass the transition from mainly elastic to plastic deformation, which is instrumentalin affecting the quality of real tablets. Using the developed model, we have explored theeffects of compression rate on the deformation behavior of the powder column, themicrostructure, and the integrity of the formed tablet. The simulations reproduced a numberof well-known effects found in tableting. At high compaction speeds and increased extent offinal compaction the system manifested a strong elastic response, giving rise to a tendencyfor the tablets to laminate on decompaction. Slower compaction speeds allowed more timefor greater internal rearrangement or plastic deformation and produced a more structurallyuniform and stable tablet at the end of the cycle. The simulations also revealed the underlyingcause for high-pressure "hot" spots and regions of weak interaction within the tablet wherefailure can occur. These points or regions invariably corresponded to incoherent interfacesbetween granule boundaries, and in some instances to interstitial atoms. The mechanicalstability of the tablet was found to depend on the effectiveness of the consolidation of thegranules, enhanced effectiveness being characterized by more coherent granule boundaries,resulting in a more uniform pressure distribution and stronger granule-granule interactions.