Formación de bandas de corte en materiales granulares: una aproximación micromecánica (original) (raw)

Shear band formation in granular materials: a micromechanical approach

abstract 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.

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.

Experimental investigation of shear band patterns in granular material

Journal of Structural Geology, 2003

This paper presents three series of sandbox experiments of extensional deformation in granular material. The dependence of the developing shear band system on different boundary conditions and material properties is investigated: (1) granulometric properties of the material, (2) initial geometry of the specimen, and (3) dynamic material parameters. Particular attention is paid to the controlling of the basal boundary conditions. X-ray technique and particle image velocimetry (PIV) are used to study the changes in the granular structure and in the formation of shear band patterns. The results show that boundary conditions are an elaborate factor to explain differences in the shear band pattern. It is shown that neither the average grain size diameter d 50 nor the rate of loading influences the shear band spacing. The spacing of the bands seems to be linearly dependent on the initial height of the specimen.

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.

Morphologies of three-dimensional shear bands in granular media

Physical Review E, 2006

The description of the rheological properties of dry granular media is a key question which controls the ability to handle (mixing, storing, transporting, etc.) these particulate systems. An interesting and sometimes annoying feature of such materials is strain localization, which appears almost always when a sample is subjected to deformation. The morphology of these narrow domains (shear bands) is far from being understood.