Shear band formation in granular materials: a micromechanical approach (original) (raw)

Formación de bandas de corte en materiales granulares: una aproximación micromecánica

Epsilon, 2009

Shear bands as mode of failure in granular soils has been largely studied without to physically explain the formation mechanism of that, neither to reproduce exactly a defined failure pattern. Several algorithms were performed with a distinct element method. In this ones, are looking for to reproduce only shear band in a biaxial simulation on rigid disk assembly, to get information at shear zone.

Computer simulation of three dimensional shearing of granular materials: Formation of shear bands

Powders and Grains 2005: Proceedings of the International Conference on Powders & Grains 2005, Stuttgart, Germany, 18-22 July 2005, 2005

ABSTRACT: We used computer simulations to study spontaneous strain localization in granular materials, as a result of symmetry breaking non-homogeneous deformations. Axisymmetric tnaxial shear tests were simulated by means of standard three-dimensional Distinct Element Method (DEM) with spherical grains. Carefully prepared dense specimens were compressed between two platens and, in order to mimic the experimental conditions, stress controlled (initially) axisymmetric boundary conditions were constructed. Strain ...

DEM Study of Shear Band Formation in Granular Materials under True Triaxial Test Conditions

2022

Subjected to external loads, granular materials experience severe deformation in a narrow zone before their failure. This phenomenon, which is called strain localisation or shear band, is of vital importance in assessing the stability of the geotechnical structure, studying the stress-strain behaviour of soil and rock materials, and analysing the interaction of soil and structure. The present study is aimed to investigate the effect of various factors on the pattern and inclination of shear band in a general threedimensional condition of stress using the Discrete Element Method (DEM). Several tests were simulated using a developed version of the TRUBAL program called GRANULE. The GRANULE code was further developed to add the capability of carrying out simulations with different intermediate principal stresses and modelling specimens containing non-spherical particles. The shear band was detected by tracking the motion of the particles and plotting the rotation distribution of particles within the sample. The results prove that the shear band inclination and its pattern, are greatly affected by intermediate principal stress, particle shape, and confining stress. Moreover, it was observed that the change in the b value plays a key role in the alteration of the 3D configuration of the shear band.

Shear band emergence in granular materials—a numerical study

International Journal for Numerical and Analytical Methods in Geomechanics, 2007

In contrast to continuum systems where localization or shear banding arises through a bifurcation in a predefined system of differential equations, shear bands emerge in numerical simulations of deforming granular systems with no prescribed mathematical relations other than simple contact forces between particles. Shear bands emerge from the self-organization of large numbers of particles with long-range geometrical interactions playing a dominant role; both translation and rotation of particles are important. Granular media therefore deform more like materials with non-local constitutive relations than materials where only first-order interactions are relevant. In this paper we adopt a thermo-mechanical approach and explore the fluxes of energy in the evolving granular system (that has cohesion as well as friction between the particles) as it is loaded through the unstable localization regime, and track the evolution of energy dissipation. As in continua, the sign of the second-order work defines the emergence of instability in the system. Initially, these instabilities decay into stable configurations of particles but with continued loading, force chains collapse locally to generate geometrically necessary fractures. These zones then propagate to generate localization zones. When these fractures form a continuous network, the system is at the percolation thresh-hold for broken bonds. However, long before this stage, the second-order work fluctuates in bursts weakly correlated with bursts in kinetic energy as damage accumulates. This behaviour suggests that any continuum constitutive description of granular media must be (i) non-local in an anisotropic manner, (ii) micro-polar, and (iii) involve damage evolution.

Formation and development of shear bands in granular material

A system of equations modeling antiplane shear in a granular material is considered. The model includes the possibility of localization of strain, and the subsequent development of shear bands. This behavior is captured in our analysis of the Riemann initial value problem, in which an initial discontinuity propagates as a combination of moving waves and a stationary shear band. The analysis is veri ed by numerical results obtained with a Godunov method including adaptive mesh re nement.

Role of sliding contacts in shear banding affecting granular materials

2019

Shear banding is a widely concerned issue caused by shearing in the field of granular geomechanics. At the macroscopic scale, the constitutive models meet difficulties to describe how and why the shear band forms within the discrete granular assembly. The contact network inside the overall granular assembly helps us to understand the origin of some macroscopic features. Between contacting particles, sliding can occur, which is associated with the plastic dissipation. This local contact sliding may induce the rearrangement of local structures, and then contribute to the macroscopic failure characterized by larger patterns, such as shear banding. In this paper, we conduct DEM simulations using a dense specimen, and during the loading process an evident shear band appears. Then the contact sliding ratio, sliding index, and the relationship between the contact sliding and the mesostructural changes are investigated. Main conclusions are: sliding contacts firstly distribute randomly with...

Effect of cyclic shearing on shear localisation in granular bodies

Granular Matter, 2004

Cyclic shearing of an infinite narrow layer of dry and cohesionless sand between two very rough boundaries under constant vertical pressure is numerically modelled with the finite element method using a polar hypoplastic constitutive relation. The constitutive relation was obtained through an extension of a non-polar model by polar quantities, viz. particle rotations, curvatures, couple stresses using the mean grain diameter as a characteristic length. The proposed model captures the essential mechanical features of granular bodies in a wide range of densities and pressures with a single set of constants. The material constants can be easily determined from granulometric properties and laboratory tests. The attention of numerical simulations is laid on the influence of number of cycles on the thickness of an induced shear zone for both an initially dense and loose granular specimen. In addition, the effect of a stochastic distribution of the initial void ratio on shear localisation is demonstrated.

Failure in shear bands for granular materials: thermo-hydro-chemo-mechanical effects

Géotechnique Letters, 2013

The failure of geomaterials in localised shear bands is one of the most common features in geomechanics. Early studies have provided the necessary criteria for the conditions of localisation, inclination angle with respect to the loading axes and thickness of the shear bands, when loaded at room temperature. This work extends these criteria for the problem of simple shear of a chemically active granular cohesionless material at higher temperatures, where thermal or chemical pressurisation may set in and influence the response of the material. It is deduced that failure occurs at higher positive values of the hardening modulus as temperature increases, that the shear band thickness also depends on the chemical reaction characteristics and that micro-inertia due to grain translations and rotations introduce the necessary rate dependency to regularise the system.

Multiple shear band development and related instabilities in granular materials

Journal of the Mechanics and Physics of Solids, 2004

A new, small-strain constitutive model, incorporating elastoplastic coupling to describe developing elastic anisotropy, and density as a state variable to capture compaction and dilation, is proposed to simulate the behaviour of granular materials, in particular sand. This developing elastic anisotropy is related to grain reorientation and is shown to be crucial to obtain localisation during strain hardening, as experiments exhibit. Post-localisation analysis is also performed under simpliÿcative assumptions, which evinces a number of features, including softening induced by localisation, size e ects and snap-back, all phenomena found in qualitative and quantitative agreement with experiments. No prior model of granular material deformation correctly captures all these behaviours.