Finite element study of particle contact mechanics and stockpiling process

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Embargoed until 2013-07-31
Copyright: Zheng, Qijun
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Abstract
Granular matter is widely used in many industrial and environmental processes but poorly understood till now. To model such matter from a discrete view point, e.g. using the so-called discrete element method (DEM), an important aspect is to accurately determine the particle-particle contact forces as they control the motions of the individual particles and accordingly, the bulk behaviour of the granular system. Although many models have been proposed to quantify the contact forces, they are, in general, lacking the consistency and sound physical basis, particularly for viscoelastic materials. On the other hand, from a continuum view point, the granular matter is more difficult to model due to its different behaviours under different conditions. A known problem that challenges the continuum approaches is the pressure dip beneath a granular heap. In spite of intensive researches in past decades, this problem still remains open for discussion. In present work, using the finite element method (FEM), we first analyse the contact forces between a viscoelastic sphere and a rigid plane, including the normal and tangential forces as well as the rolling friction. The results show that previous models for viscoelastic materials are all problematic in one aspect or the other. Based on a theoretical derivation in the framework of contact mechanics and the FEM results, a new set of models are proposed to describe the contact behaviour of viscoelastic spheres. To gain more generality, the new models are then extended to account for the contact of non-spherical particles which are testified in impacts of two ellipsoids. This work also tries a novel approach, i.e. the finite element method of Eulerian formulation, to investigate the above mentioned problem of the pressure dip. This approach allows us to model the whole construction process of a pile as in experiments, which can therefore record the deformation history of the material automatically. Of interest is the fact that such a method, together with the Mohr-Coulomb or Drucker-Prager elastoplastic models is able to reproduce the pressure dip as well as other experimental observations. A parametric study further shows that the emergence of the pressure dip could be affected by both experimental conditions and material properties. This work can be regarded as a support for traditional elastoplastic approaches in the studies of granular matter.
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Author(s)
Zheng, Qijun
Supervisor(s)
Yu, Aibing
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Publication Year
2012
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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