YIELD AND DEFORMATION OF AN ASSEMBLY OF DISKS SUBJECTED TO A DEVIATORIC STRESS LOADING

The deformation of an assembly of particles is examined using a discre te element method (DEM) numerical model. The particles are modeled as random-sized, rough, inelastic, circular two-dimensional disks. The si mulations keep track of the displacements, velocities and contact forc es of each particle in order to examine the local rearrangements of th e particles during the deformation and to determine the bulk stress st ates. The behavior of cohesive materials can be examined by introducin g tensile forces between particles. The tests are done by applying con stant confining pressures on two parallel flexible boundaries and a co nstant displacement rate on the two other flat frictionless walls. Dur ing the loading, the axial stress on the moving walls reaches a peak v alue and afterwards remains essentially constant for large strains. St ress-strain curves are obtained for a large range of confining pressur es. They show that the yield envelopes follow the linear Mohr-Coulomb criterion. The global angle of friction is determined for a large rang e of particle-particle friction angles and particle size distributions . It was found that the global friction angle phi(cv) increased with i nterparticle friction angle phi(1) for phi(i) < 6 degrees; for larger values of phi(i), the global friction angle is essentially constant. A s the spread in the particle size distribution increased, the magnitud e of the internal angle of friction was found to increase for a given interparticle friction angle. (C) 1998 Elsevier Science Ltd.