Nonconvex Models of Consolidation by Particle Rearrangement in Cohesive Aggregates

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The objective of this research is to understand the physics of multiphase consolidation of fine particulate aggregates and to develop and calibrate predictive models of consolidation. At the focus of the research is the first 30 to 45 percent of the consolidation stroke, where the consolidation is dominated by particle rearrangement, which has been shown to occur in the form of a phase transition. A tensorial model of consolidation by particle rearrangement will be formulated using homogeneization methods and nonconvex analysis. To test and calibrate the model independent of the effect of die-wall friction, consolidation curves will be measured in punching experiments devoid of a characteristic lengthscale, and a method to extract the value of the transition stress from a single consolidation curve will be developed. The effect of die-wall friction will then be included in order to predict consolidation curves in cylindrical dies, which will be compared with the consolidation curves of common pharmaceutical fillers. For dies of a more complicated geometry, a computational code will be developed for the simulation of cohesive aggregation and a discrete-particle computational code for the simulation of multiphase consolidation.The methods and computational programs developed as part of this research will be applicable to the forming of ceramic parts, powder metallurgical components, and pharmaceutical tablets, where the design of consolidation procedures has remained a trial-and-error process, and where accounting for the inhomogeneous nature of particle rearrangement may lead to reliable design. The research may help reduce waste in industrial processes such as granulation, in which 20 percent of the powders must be recycled due to incomplete consolidation. The research is also relevant to the computation of the subsidence history of sedimentary basins, of critical importance in oil prospecting. The experimental plan will provide opportunities for the participation of undergraduate students, and both graduate and undergraduate students will benefit through classroom instruction.