Effect of cohesion on local compaction and granulation of sheared soft granular materials

Roy, Sudeshna; Luding, Stefan; Weinhart, Thomas

doi:10.1051/epjconf/201714003065

Cited by 7 publications

(9 citation statements)

References 13 publications

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“…The volume fraction increases with increase in confining stress as shown in [27,40]. In ongoing research [34], we show that inter-particle cohesion has a considerable impact on the compaction of the soft materials. Cohesion causes additional stresses, due to capillary forces between particles, leading to an increase in volume fraction due to higher compaction.…”

Section: Rheological Modelsupporting

confidence: 56%

“…where b = 0.6 for non-cohesive materials and b < < 0.5 0.7 for cohesive materials are fitted well by our data. Assuming the pressure varying hydrostatically and the bulk density as r r » 0.6 b , we translate equation (34) to W as a function of p. Substituting equations (31) and (34) in (13) and rearranging, we get the inertial number I max in the shear band center as a function of the local pressure p. Further, by substituting p, we get h* max in the shear band center and thus obtain a quantitatively accurate prediction of h* max (I max ), plotted as blue solid lines and cyan dashed lines in figure 10.…”

Section: Analytical Prediction Of Apparent Viscositymentioning

confidence: 99%

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A general(ized) local rheology for wet granular materials

2017

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We study the rheology of dry and wet granular materials in the steady quasistatic regime using the discrete element method in a split-bottom ring shear cell with focus on the macroscopic friction. The aim of our study is to understand the local rheology of bulk flow at various positions in the shear band, where the system is in critical state. We develop a general(ized) rheology, in which the macroscopic friction is factorized into a product of four functions, on top of the classical ( ) m I rheology, each of which depends on exactly one dimensionless control parameter, quantifying the relative importance of different micro-mechanical machanisms. These four control parameters relate the time scales of shear rateġ t , particle stiffness t k , gravity t g and cohesion t c , respectively, with the governing time scale of confining pressure t p . Whileġ t is large and thus of little importance for most of the slow flow data studied, it increases the friction in critical state, where the shear rate is high and decreases friction by relaxation (creep) where the shear rate is low. t g and t k are comparable to t p in the bulk, but become more or less dominant relative to t p at the extremes of low pressure at the free surface and high pressure deep inside the bulk, respectively. The effect of wet cohesion on the flow rheology is quantified by t c decreasing with increasing cohesion. Furthermore, the proposed rheological model predicts well the shear thinning behavior both in the bulk and near the free surface; shear thinning rate becomes less near the free surface with increasing cohesion.

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Section: Rheological Modelsupporting

confidence: 56%

Section: Analytical Prediction Of Apparent Viscositymentioning

confidence: 99%

A general(ized) local rheology for wet granular materials

2017

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“…The setup used for simulations consists of a shear cell with annular geometry and a split in the bottom plate, as explained in [15,17,18,22,[30][31][32][33][34]. The system consists of an outer cylinder (radius R o = 110 mm) rotating around a fixed inner cylinder (radius R i = 14.7 mm) with a rotation frequency of = 0.19 s −1 .…”

Section: A Geometrymentioning

confidence: 99%

“…The granular material is confined by gravity between the two concentric cylinders and the bottom plate, with a free top surface. [15,18,22], very few simulations are done using the whole shear cell [35,36].…”

Section: A Geometrymentioning

confidence: 99%

“…This bulk cohesion was analyzed in terms of the force and fabric anisotropies [21] for wet granular materials. In our previous studies, a generalized rheology shows that the steady-state shear stress is factorized into a product of functions of different dimensionless numbers [18,22], if a simplistic situation is assumed where all contacts have an equal liquid bridge volume. The liquid in the system is then not treated as a separate entity; rather the contact model takes into account the effect of liquid capillary bridges.…”

Section: Introductionmentioning

confidence: 99%

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Liquid redistribution in sheared wet granular media

2018

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Shearing wet granular systems causes a redistribution of the interstitial liquid, which can affect the material's bulk behavior. Using the discrete-element method, we study the early rapid transients, the intermediate states, and the slow long-term evolution of liquid redistribution for various material parameters and different initial wetting conditions in an inhomogeneous split-bottom ring-shear cell featuring a wide shear band away from the system walls. In our model, liquid exists in two states, either in liquid bridges between particles or in liquid films on the particle surfaces. Under deformations like shear, the liquid is redistributed due to the rupture of existing and formation of new liquid bridges. Since we assume the immediate redistribution limit as a new model parameter, a liquid bridge limit volume is imposed to avoid extensive clustering of liquid. Studying the effect of the local shear rate on the liquid redistribution, two distinct effects are observed: For small amounts of shear, i.e., small strain amplitude, the interstitial liquid is randomly redistributed locally, and for larger amounts of shear, liquid is transported away from the shear zone. The local redistribution quickly results in a characteristic probability distribution of liquid bridge volumes, independent of the initial wetting conditions, but the mean and the shape of the distribution are dependent on the limit volume. Although the shear-driven diffusion-like liquid transport is active from the beginning, it dominates the transport in the long term, when the liquid moves out of the shear band, making the shear band dry. Ongoing theoretical analysis suggests a competition of drift and diffusive mechanisms in a different set of coordinates that can explain all our observations by defining a local Péclet number that quantifies the relative strength of the two transport mechanisms.

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DEM analyses of cemented granular fault gouges at the onset of seismic sliding: peak strength, development of shear zones and kinematics

Casas

Mollon

Daouadji

2021

Preprint

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Fault zones usually present a granular gouge, com-ing from the wear material of previous slips. This layer contributes to friction stability and plays a key role in the way elastic energy is released during sliding. Considering a mature fault gouge with a varying amount of mineral cementation between particles, we aim to understand the influence of the strength of interparticle bonds on slip mechanisms by employing the discrete element method. We consider a direct shear model without fluid in 2D, based on a granular sample with angular and faceted grain shapes. Focusing on the physics of shear accommodation inside the granular gouge, we explore the effect of an increase of cementation on effective fric-tion (i.e. stress ratio) within the fault. We find that brittleness and the overall shear strength are enhanced with cementation, espe-cially for dense materials. For the investigated data range, three types of cemented material are highlighted: a poorly cemented material (Couette flow profile, no cohesion), a cemented material with aggregates of cemented particles changing the granular flow and acting on slip weakening mechanisms (Riedel shear bands R), and a highly-cemented material behaving as a brittle material (with several Riedel bands followed by fault-parallel shear-localization Y). Effective friction curves present double weakening shapes for dense samples with enough cementation. We find that the effective friction of a cemented fault cannot be directly predicted from Mohr-Coulomb criteria because of the heterogeneity of the stress state and kinematic constraints of the fault zone.

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Effect of cohesion on local compaction and granulation of sheared soft granular materials

Cited by 7 publications

References 13 publications

A general(ized) local rheology for wet granular materials

A general(ized) local rheology for wet granular materials

Liquid redistribution in sheared wet granular media

DEM analyses of cemented granular fault gouges at the onset of seismic sliding: peak strength, development of shear zones and kinematics

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