Discrete element methodology for the analysis of cohesive granular bulk solid materials, A

Abstract

In bulk handling applications, such as conveying and storage, understanding the effect cohesion has upon the flow-ability of particulate systems at the macroscopic scale is crucial in increasing the avenues of operation unit design improvements and handling scenarios of industrial operational units. This research provides a better understanding of the role cohesion has on the flow-ability of macro materials through the development, implementation and application of a macroscopic elasto-plastic adhesive (MEPA) contact model within an open source general purpose Discrete Element Method (DEM) computer code. This dissertation outlines the development of a DEM contact law which can model stress history dependent strength behavior of cohesive particulate systems and predict its effects upon the particulate flow. The research tasks in this work are focused in three major areas: 1) cohesive function applications from powders to bulk solids, 2) modeling stress history dependency of cohesive strength, and 3) the prediction of flow properties in test applications that are comparable to experimental results. For a given bulk handling application, adequately capturing the DEM simulated behavior of cohesive solids is crucial when evaluating its handle-ability. A number of DEM micro mechanically-based cohesive contact laws are available; however, these do not model the stress history dependent behavior physically observed in particulate bulk solids. A study of these micro mechanically-based cohesive models revealed that most of these models are focused on simulating the effects of cohesion in powder systems. A major shortcoming of these micro mechanically-based models is the iterative parametric scaling needed to represent cohesive-like behavior. When simulating the handling difficulties caused by cohesion, it is apparent that modelling stress history dependency is crucial in consolidated materials with high cohesive strength. This investigation proposed a DEM history dependent particle-particle MEPA contact model that accounts for both elastic and plastic contact deformations and adhesive attractions. The MEPA model applied herein is a three branched non-linear contact model that simulates the virgin compaction loading, unloading/reloading and adhesion behavior of a particulate solid. The culmination of this research is a general purpose DEM high performance computer code, LIGGGHTS that includes an enhanced capability for material flow simulations of highly cohesive particulate systems for modeling industrial bulk solids handling applications.