This paper focuses on the columnar particle structures known as force chains, and their failure via buckling. The local kinematics and frictional dissipation of this failure mechanism are examined quantitatively for dense, cohesionless granular assemblies, under quasistatic and strain-controlled compression. Data are taken from a physical experiment and a discrete element simulation of bidisperse assemblies of circular particles undergoing shear banding. Particular attention is paid to the deformation and dissipation within a class of particle clusters, each composed of a buckled force chain segment and its laterally supporting neighbours. These particle clusters are found to be confined to the shear band. We establish measures of their local micropolar deformation, including nonaffine deformation, and the evolution of these quantities with strain. Temporally and spatially, the kinematics of this class of particles exhibits trends consistent with the particle motions that form the major contributors to de...

Buckling force chains in dense granular assemblies: physical and numerical experiments

This paper presents the results of a comprehensive study of the effects of rolling resistance on the stress–strain and strain localization behavior of granular materials using the discrete element method. The study used the Particle Flow Code (PFC) to simulate biaxial compression tests in granular materials. To study the effects of rolling resistance, a user-defined rolling resistance model was implemented in PFC. A series of parametric studies was performed to investigate the effects of different levels of rolling resistance on the stress–strain response and the emergence and development of shear bands in granular materials. The PFC models were also tested under a range of macro-mechanical parameters and boundary conditions. It is shown that rolling resistance affects the elastic, shear strength and dilation response of granular materials, and new relationships between rolling resistance and macroscopic elasticity, shear strength and dilation parameters are presented. It is also concluded that the rolling resistance has significant effects on the orientation, thickness and the timing of the occurrence of shear bands. The results reinforce prior conclusions by Oda et al. (Mech Mater 1:269–283, 1982) on the importance of rolling resistance in promoting shear band formation in granular materials. It is shown that increased rolling resistance results in the development of columns of particles in granular materials during strain hardening process. The buckling of these columns of particles in narrow zones then leads to the development of shear bands. High gradients of particle rotation and large voids are produced within the shear band as a result of the buckling of the columns.

Comprehensive study of the effects of rolling resistance on the stress–strain and strain localization behavior of granular materials

A stress dilatancy model with embedded microstructural information, originally developed by the writers, is used to illustrate the pivotal importance of dilatancy and fabric on the behavior of sand. Fabric, as a second-order tensor, enters into the stress dilatancy equation obtained from a microscopic analysis of an ensemble of rigid particles. Model simulations of sand behavior are carried out in triaxial stress conditions along strain paths with varying degrees of controlled dilation ~or compaction! including isochoric deformations as a particular case. Under particular strain paths and fabric conditions, it is shown that a relatively dense sand can succumb to instability or liquefaction under other than isochoric ~undrained! conditions. This phenomenon is in accord with laboratory experiments in which dilation or compaction is controlled by modulating the amount of water flowing in or out of a sand specimen during shearing. Mixed drained-undrained loading paths are also simulated with particular reference to fabric dependence at a fixed void ratio. Model simulations capture most of the observed characteristics of sand response, such as instability and asymptotic behavior under various conditions.

https://people.ucalgary.ca/~wan/Journal_Preprints/ASCE_EMD2004.pdf

Stress Dilatancy and Fabric Dependencies on Sand Behavior

Internal short circuit and failure mechanisms of lithium-ion pouch cells under mechanical indentation abuse conditions：An experimental study

In this paper, the phenomenon of strain localization, i.e., shear banding, in densely distributed metallic assemblies has been studied. A discrete element methodology for analyzing metallic granular materials has been put forward. In this numerical model, elastoplastic contact, as well as friction, rolling resistance and cohesion between spheres, are explicitly taken into account. The calculations reveal that the shear banding mechanism in dense assemblies can be thought as an instability triggered by initial imperfections. Within a band, the motion, deformation and rearrangement of spheres soften the resistance of the aggregate, as these mechanisms create additional geometric imperfections. Additionally, the simulations showed that the shear-band width does not change conclusively with the friction, rolling resistance and plasticity parameters. However, cohesive strength, even in small amounts, drastically increased the shear-band width. Finally, the shear-band thickness and inclination angles are strongly dependent on the degree of initial imperfection. Whereas for a perfect assembly the shear band inclinations were consistently around 60degrees, more heterogeneous assemblies lead to shear band angles closer to the continuum mechanics solution, which is 45degrees. This was found to be in agreement with recent experimental observations. (C) 2003 Elsevier Ltd. All rights reserved.

H Kazama

Papers

Effects of induced anisotropy on the development of shear bands in granular materials