Shear bands in dense metallic granular materials

Hu, Ningning

doi:10.1016/j.jmps.2003.08.003

Cited by 57 publications

(27 citation statements)

References 27 publications

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“…As will be seen below, these "wakes" seem to derive from the main vortices. While opposite direction particle slip and/or rotation has been detected in experiments [5] and simulations [28], coordinated grain motion, in particular in the form of counterrotating wakes as seen in Fig. 6c, was not reported.…”

Section: Residual Displacementsmentioning

confidence: 72%

Vortex formation and dissolution in sheared sands

2012

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Using digital image correlation, we track the displacement fluctuations within a persistent shear band in a dense sand specimen bounded by glass walls undergoing plane strain compression. The data evidences a clear, systematic, temporally recurring pattern of vortex formation, dissolution, and reformation throughout macroscopic softening and critical state regimes. During softening, locally affine deformation zones are observed at various locations along the shear band, which we argue to be kinematic signatures of semi-stable force chains. Force chain collapse then occurs, inducing vortex formation. Local jamming at the conflux of opposing displacements between adjacent vortices arrests the vortices, providing an avenue for potential new force chains to form amidst these jammed regions. The process repeats itself temporally throughout the critical state. The pattern further correlates with fluctuations in macroscopic shear stress. We characterize the nature of the observed vortices, as they are different in our sands comprised of irregular shaped particles, as compared to previous observations from experiments and numerical simulations which involved circular or rounded particles. The results provide an interesting benchmark for behavior of non-circular/non-spherical particles undergoing shear.

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Section: Residual Displacementsmentioning

confidence: 72%

Vortex formation and dissolution in sheared sands

2012

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“…Thus, in general, it is important to have some way of accounting for the effects of particle shape in DEM simulations-at the very least a way by which relative rotations at contacts may be reasonably controlled. The introduction of a frictional contact moment or rolling resistance allows the modeler to regulate this important aspect of material behavior and achieve particle rotations that would otherwise be unrealistically high, while still retaining the simplest particle geometry and the advantage of low computational cost [14,[34][35][36].…”

Section: Numerical Simulationmentioning

confidence: 99%

Stress–dilatancy and force chain evolution

Tordesillas

Shi

Tshaikiwsky

2011

Num Anal Meth Geomechanics

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SUMMARYThe evolution of internal structure plays a pivotal role in the macroscopic response of granular materials to applied loads. A case in point is the so-called 'stress-dilatancy relation', a cornerstone of Soil Mechanics. Numerous attempts have been made to unravel the connection between stress-dilatancy and the evolution of fabric and contact forces in a deforming granular medium. We re-examine this connection in light of the recent findings on force chain evolution, in particular, that of collective force chain failure by buckling. This study is focussed on two-dimensional deformation of dense granular assemblies. Analysis of individual and collective force chain bucklings is undertaken using data from a discrete element simulation. It is shown that the kinematics of force chain buckling lead to significant levels of local dilatation being developed in the buckling force chain particles and their confining first-ring neighbors. Findings from the simulation are used to guide the development of a lattice model of collective, localized force chain buckling. Consideration of the statics and kinematics of this process yields a new stress-dilatancy relation. The physics of buckling, even at its simplest form, introduces a richness into the stress-dilatancy formulation in a way that preserves the essential aspects of fabric evolution, specifically the buckling mode.

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“…Anand and Gu, 2000;Gudehus and Nubel, 2004). For heterogeneous materials, the presence of preliminary or ''temporary'' shear bands has been attributed to local failure due to local, minor density variations (Gudehus and Nubel, 2004) or initiated by minor geometric material non-uniformities (Hu and Molinari, 2004). Such minor density variations or non-uniformities are likely responsible for producing the complex, non-uniform deformation patterns seen in the pre-peak increments of Fig.…”

Section: Patterns Of Shear Band Formation and Evolutionmentioning

confidence: 99%