Modeling of Powder Compaction: A Review

Abstract

The compaction process involves stress transmission via rigid or flexible (die) walls and the propagation of stresses within a powder mass. The particles that comprise the powder distribute the stress by a variety of kinematic processes that involve sliding, rotation, particle deformation, and rupture. In practice the “particles” are often agglomerates of finer particles that have a range of properties. All of these factors must be considered in developing a comprehensive predictive model for compaction.The modeling of powder-compaction processes has a significant history that has been greatly advanced by the relatively recent general availability of powerful computers and their peripherals as well as by appropriate softwares. Compaction modeling may attempt to provide a basis for machine-loading specifications, or it may provide guidelines to help minimize “capping” defects where failure cracks form at the top of the green compact. It may also provide “green-body heterogeneity” through predicted stress and density distributions within a compact. Likewise compaction models may be combined with binder burnout and sintering models to predict internal microstructural features such as grain size and porosity, and the external shape of the sintered product. This article will deal only with the modeling of the compaction process; important elements such as powder flow for die filling and subsequent processing steps such as sintering and net shape predictions are not directly addressed.

Prediction of Tablet Characteristics from Residual Stress Distribution Estimated by the Finite Element Method

“…The Drucker–Prager Cap (DPC) model is one of the continuum mechanical models in which the powder is considered a porous medium. The DPC model can represent the densification and hardening of the powder, as well as the interparticle friction . The DPC model is therefore frequently used to analyze the strain, relative density changes, and stress distribution of tablets during the tableting process .…”

“…The DPC model can represent the densification and hardening of the powder, as well as the interparticle friction. 6,7 The DPC model is therefore frequently used to analyze the strain, relative density changes, and stress distribution of tablets during the tableting process. [8][9][10] The DPC model is characterized by parameters such as cohesion, internal friction angle, Young's modulus, Poisson ratio, parameters related to volume change and hardening mechanisms, and so on.…”

A modified Drucker-Prager Cap model for die compaction simulation of pharmaceutical powders

“…phenomenological models. The phenomenological models, such as critical state models like Cam-Clay plasticity models and Cap plasticity models, which were originally developed for geological materials in soil mechanics, turned out to be well suited for modelling powder compaction, especially in powder metallurgy (Aydin et al, 1997(Aydin et al, , 1996Chtourou et al, 2002;Coube and Riedel, 2000;PM-Modnet-Modelling-Group, 1999). More recently, Drucker-Prager Cap plasticity models have been used for the analysis of compaction of pharmaceutical powders, because they can represent the densification and hardening of the powder, as well as the interparticle friction Frenning, 2007;Michrafy et al, 2004Michrafy et al, , 2002Sinka et al, 2003Sinka et al, , 2004Wu et al, 2005Wu et al, , 2008.…”

“…A method to determine shear failure line from die compaction tests(Aydin et al, 1997): (a) loading path plotted on the p À q space; (b) axial stress-axial strain curve.…”

Effect of Process Variables on the Drucker–Prager Cap Model and Residual Stress Distribution of Tablets Estimated by the Finite Element Method

“…The DPC model can represent the densification and hardening of the powder, as well as the interparticle friction. 7,8) This model can also reasonably represent both the shear failure and the plastic yielding of the powder, and can be readily characterized via experiments on real powders. Therefore, the DPC model is used frequently to analyze the strain, relative-density changes, and stress distribution of tablets during the tableting process.…”