Nonconvex Models of Consolidation by Particle Rearrangement in Cohesive Aggregates

本研究的目的是了解细颗粒集料的多相固结的物理特性，并开发和校准固结的预测模型。 研究的重点是固结冲程的前30%至45%，其中固结由颗粒重排主导，这已被证明以相变的形式发生。本文将利用离散化方法和非凸分析建立颗粒重排固结张量模型。为了测试和校准的模型独立的模具壁摩擦的影响，固结曲线将被测量在冲孔实验缺乏一个特征的长度尺度，和一种方法来提取从一个单一的固结曲线的过渡应力的值将被开发。然后，将包括模壁摩擦的影响，以预测在圆柱形模具中的固结曲线，这将与常见的药用填料的固结曲线进行比较。对于更复杂几何形状的模具，将开发用于模拟内聚聚集的计算代码和用于模拟多相固结的离散颗粒计算代码。作为本研究的一部分开发的方法和计算程序将适用于陶瓷零件、粉末冶金零件和药片的成形，其中固结过程的设计仍然是一个试错过程，并且其中考虑到颗粒重排的不均匀性质可能导致可靠的设计。这项研究可能有助于减少造粒等工业过程中的浪费，其中20%的粉末由于不完全固结而必须回收。该研究还与计算沉积盆地的沉降历史有关，这在石油勘探中至关重要。实验计划将为本科生的参与提供机会，研究生和本科生都将通过课堂教学受益。

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.