Contact Transience during Slow Loading of Dense Granular Materials

Abstract

The irregularity of particle motions during quasi-static deformation is investigated using discrete element (DEM) simulations of of sphere and sphere-cluster assemblies. Three types of inter-particle movements are analyzed: relative motions of particle centers, relative motions of material points of two particles at their contact, and the traversal of contacts across the surfaces of particles. Motions are a complex combination of rolling, sliding, and elastic distortion at the contacts, and all motions are highly irregular and variant, qualities that increase with increasing strain. The relative motions of particle centers diverges greatly from those of an affine displacement of the particles. The motions of the non-convex sphere-cluster particles was more regular that those of spheres. The paper also investigates the effect of the distance between two remote particles and their pair-wise relative displacements. Even for particle-pairs separated by more than 6 intermediate particles, the relative motions do not conform with the mean deformation (affine) field. Force chains are shown to be transient features, which survive only briefly across elapsed strains.

Dependency of Dilatancy Ratio on Fabric Anisotropy in Granular Materials

“…A 3D clumped particle is created by rigidly connecting two identical overlapping spherical particles. The efficacy of clumped particles in representing the behavior of sand has been justified in numerous studies (e.g., Kuhn 2017;Li et al 2016). A traditional linear elastic-plastic contact law (Cundall and Strack 1979) is used for interparticle contact in the 3D tests, with K n ¼ 5 × 10 5 r kN=m 2 and K s ¼ 0.3K n , where r equals the radius of the particle.…”

Multi-directional behavior of granular materials and its relation to incremental elasto-plasticity

“…These hypothetical models also lead to tangential plasticity, although they presume a single, averaged behavior to all contacts with the same orientation, assume affine movements among the particles, and homogenize movements across the space of orientations. Recent DEM simulations have shown, however, that micro-scale movements are irregular and non-affine, with particles seemingly darting and dodging in a highly irregular manner, and that contact movements are highly diverse, even when one considers a subset of contacts having the same orientation [57,58,59]. Moreover, a fraction of contacts are persistently non-elastic and continue to undergo frictional slip even when the direction of bulk deformation is reversed [24].…”

Operational Variables on the Processing of Porous Titanium Bodies by Gelation of Slurries with an Expansive Porogen

“…In this test the applied compressive force distributes inside the sample transmitting the applied force in a simple elastic-plastic behavior [ 39 ]. The dome configuration makes the compressive forces to develop circular tensile stresses on the surface of the sample [ 40 , 41 , 42 ]. It has to be noted that this analysis considers a homogeneous and isotropic pore distribution without pore orientation, but orientation arising from the processing technologies can conditions the mechanical properties [ 43 ].…”

“…The final evolution of the force-strain curve (Zone III) can be identified with a densification process forced by the uniaxial pressure that compression plates exert onto the broken sample. As the broken pieces are not confined into a die, the Zone III can’t be clearly identified [ 40 ]. In this study we were focused on the Zones I and II where the structural integrity of green sponges is mainly conditioned by the porosity and then by the selected operation variables (X G , X P and X T ).…”