Abstract

This paper aims at characteristic failure mechanisms of cohesive frictional materials at two levels of observation: (a) at the macroscale of continuum elastoplasticity, and (b) at the microscale of active microplanes with arbitrary orientation. Thereby, the criteria for the loss of uniqueness and the loss of ellipticity will be discussed for a macroscopic as well as a microplane-based anisotrop...

We use plate drag to study the response of granular media to localized forcing as a function of volume fraction, φ. A bifurcation in the force and flow occurs at the onset of dilatancy, φc. Below φc rapid fluctuations in the drag force, FD, are observed. Above φc fluctuations in FD are periodic and increase with φ. Velocity field measurements indicate that the bifurcation in FD results from the...

We investigate the macroscopic properties of frictionless nonconvex particles using molecular dynamics. The calculations are based on a simple and efficient method to simulate complex-shaped interacting bodies. The particle shape is represented by Minkowski operators. A multicontact time-continuous interaction between bodies is derived using simple concepts of computational geometry. Three-dime...

We introduce a simple model to describe the frictional properties of granular media under shear. We model the friction force in terms of the horizontal velocity ẋ and the vertical position z of the slider, interpreting z as a constitutive variable characterizing the contact. Dilatancy is shown to play an essential role in the dynamics, inducing a stick-slip instability at low velocity. We compu...

How does pore liquid reconfigure within shear bands in wet granular media? Conventional wisdom predicts that liquid is drawn into dilating granular media. We, however, find a depletion of liquid in shear bands despite increased porosity due to dilatancy. This apparent paradox is resolved by a microscale model for liquid transport at low liquid contents induced by rupture and reconfiguration of ...

We propose a simple continuum model to interpret the shearing motion of dense, dry and cohesion-less granular media. Compressibility, dilatancy and Coulomb-like friction are the three basic ingredients. The granular stress is split into a rate-dependent part representing the rebound-less impacts between grains and a rate-independent part associated with long-lived contacts. Because we consider ...

We use plate drag to study the response of granular media to localized forcing as a function of volume fraction ϕ. A bifurcation in the force and flow occurs at the onset of dilatancy ϕc. Below ϕc rapid fluctuations in the drag force F(D) are observed. Above ϕc fluctuations in F(D) are periodic and increase in magnitude with ϕ. Velocity field measurements indicate that the bifurcation in F(D) r...