Modeling of Powder Compaction: A Review
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are two- or three-dimensional and are normally continuum-based, meaning that the discrete particle effects/characteristics are not directly addressed in the modeling. Distinct or discrete models specifically consider particle-particle and particle-wall interactions. Boundaryelement models provide a convenient route for handling the large strains generated in certain compaction processes. Choosing the appropriate model or modeling approach depends on many factors, including the engineering requirements, the availability of the necessary "input" data for the model, and the available means for validating the model predictions. All models require "materials" input data for both the wall (i.e., die) and the bulk-powder and compact "rheology." A simple model like J-W requires a wall friction coefficient and a stress-volume constitutive relationship for the bulk material. More refined models require more input data—say a description of the elastic response or a more accurate description of the boundary condition. The value and the predictive capacity of any model are entirely dependent on the availability and reliability of the required materials input data. Additionally confidence in model predictions hinges on model validation, which requires experimentally characterizing the compact and the compaction process. This overview will demonstrate that computer models with varying levels of sophistication can now provide a close and practically useful description of compaction processes. Options for modeling compaction and their predictive potential are reviewed. Predictions of wall stresses, stress and density distributions within a compact, and green shape are compared with experimental measurements. Additionally the "input" data
required to model compaction will be summarized. Modeling Powder Compaction To model powder compaction, one must determine the states of stress, the strain, and the displacements in a powder body subjected to interface forces, interface displacements, and body forces at the die (boundary) interfaces as well as the way they propagate through the powder body. In choosing suitable constitutive models to describe the deformation behavior of powders during compaction, the material's response to the environment and the applied stress states must be considered. This includes (1) the yielding, hardening, and failure characteristics of the "frictional" and "compressible" powder during compaction; (2) the large strain formulation of the powder bed under compaction; (3) the friction at the interface of the powder and the die wall; and (4) the elastic recovery within the compact upon the completion of the compaction process. With this information, it is possible to determine the evolution of the internal and external structural states of a powder compact and to describe the response of the tooling (dies) during the compaction process. The following section reviews the constitutive models currently available for powder materials and the numerical methods that may be used for their implementation. Constitutive
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