Doctoral Dissertations

Date of Award

8-2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Civil Engineering

Major Professor

Dayakar Penumadu

Committee Members

Eric C. Drumm, George M. Pharr, Roberto S. Benson

Abstract

The mechanics of granular material is an important issue that governs many geotechnical engineering applications. Two types of particles having similar particle size, but different shape are used in this research to evaluate the role of particle morphology on the physical properties of its assemblage. Experimentation of 1-D compression behavior at constant axial strain rate under laterally confined conditions is performed for these two particulate materials and the behavior of the stress path is analyzed in relation to the initial material packing and physical characteristics of the granules.

The behavior of granular assemblages under imposed loading conditions are also evaluated by analyzing the macro and micro level morphological changes (in terms of shape and size distribution) resulting from 1-D compression tests. Various experimental procedures and techniques are employed for characterizing the size and shape aspect of these particles. The mechanical properties (hardness, modulus, and time dependent creep parameters) of the individual particles are determined and analyzed using nanoindentation technique. Nanoindentation has emerged recently as a powerful tool for precise measurements of mechanical properties of materials. Considering its potential applicability in the broad area of micromechanics associated with granular materials, an in-depth study of its application is performed. Since a rigorous study of the nanoindentation technique for finite size particles has not been done to date, initial testing for developing appropriate experimental and interpretation procedures required testing reference material such as fused quartz and novel composite materials to gain additional insight and experience. For this reason, besides granular materials, the changes in mechanical properties for structured materials (blended single wall carbon nanotube-epoxy composite specimens) are also included in this research

The micromechanical analysis of granular assembly using computer simulation through the program PFC2D (2-Dimensional Particle Flow Code), an application of Distinct Element Method (DEM) is also performed. The material micro-properties such as particle shear stiffness and normal stiffness values are assigned from the nanoindentation test results for the two granular materials. The particle contact behavior, nature of force chain structure, and uniformity of deformation associated with 1-D compression on granular materials having different shape and mechanical properties are analyzed.

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