The micro-structural approach, which relates the mechanical behavior of a material to its micro-fabric and the properties of the constituent particles, is a more rational way of modeling the mechanics of granular materials. Within this approach is the numerical simulation method in the framework of the Discrete Element Method (DEM) of analysis. Instead of a continuum, DEM treats granular material as an assemblage of distinct particles, each governed by the laws of classical mechanics. Deformation analysis of inter-particle contacts does not imply continuity at particle boundaries. As this technique has evolved, it has been used in a wide variety of research applications in mechanics and Geotechnical engineering. However, there are some drawbacks to its use especially in the simulation and interpretation of real granular material behavior. Inadequate understanding of the micro-kinematics of particle rotation and contact rolling have rendered most DEM models ineffective in translating its usefulness to the overall study of the mechanics of granular assemblies. This study evaluated DEM analysis for the purpose of improving computer simulation models of granular materials in order to enhance the capability of predicting real granular behavior and its usefulness as an alternative to full-scale modeling. Implicit and explicit numerical integration algorithms are discussed on the basis of a generalized collocation formulation. In relation to DEM, it is shown that the explicit velocity Verlet method improves convergence, stability and accuracy. Using the concept of rolling friction, closed-form expressions were derived for contact rolling stiffness for both 2-D and 3-D problems. The developed DEM simulation model shows that the effects of rolling friction on the stress-strain behavior, shear strength and the development of shear bands are very significant. The study proves that simulation of granular media is greatly enhanced and the microstructure and micro-mechanisms are better revealed. Validation tests showed good agreement between DEM simulation results and available experimental tests on rod assemblies. Comparisons of heterogeneous deformation fields and the uniform strain fields indicate the need to incorporate a high gradient of strain theory in predicting the constitutive law of granular materials.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-4188 |
| Date | 01 January 1996 |
| Creators | Acheampong, Kofi Boakye |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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