Investigations of vortex structures in granular materials under earth pressure conditions by DEM

The evolution of shear zones in initially medium dense cohesionless sand for quasi-static earth pressure problems of a retaining wall was analysed with a 3D discrete element method DEM using spheres with contact moments. The passive sand failure for a very rough retaining wall undergoing horizontal translation was discussed. Attention was paid to vortex and anti-vortex structures appearing in granular shear zones. Three different methods were introduced to find granular vortices

Of cuts and cracks: data analytics on constrained graphs for early prediction of failure in cementitious materials

Using data from discrete element simulations, we develop a data analytics approach using network flow theory to study force transmission and failure in a ‘dog-bone’ concrete specimen submitted to uniaxial tension. With this approach, we establish the extent to which the bottlenecks, i.e., a subset of contacts that impedes flow and are prone to becoming overloaded, can predict the location of the ultimate macro-crack. At the heart of this analysis is a capacity function that quantifies, in relative terms, the maximum force that can be transmitted through the different contacts or edges in the network. Here we set this function to be solely governed by the size of the contact area between the deformable spherical grains. During all the initial stages of the loading history, when no bonds are broken, we find the bottlenecks coincide consistently with, and therefore predict, the location of the crack that later forms in the failure regime after peak force. When bonds do start to break, they are spread throughout the specimen: in, near, and far from, the bottlenecks. In one stage leading up to peak force, bonds collectively break in the lower portion of the specimen, momentarily shifting the bottlenecks to this location. Just before and around peak force, however, the bottlenecks return to their original location and remain there until the macro-crack emerges right along the bottlenecks

FE-INVESTIGATIONS ON SHEAR LOCALIZATIONS IN GRANULAR BODIES WITHIN HYPOPLASTICITY

Summary A spontaneous shear localization in granular bodies is investigated with a finite element method based on a hypoplastic constitutive model. To simulate properly the formation of shear zones, a hypoplastic model was extended by polar, non-local and gradient terms to take into account a characteristic length of the microstructure. Two different rate boundary value problems were numerically analyzed with an extended model

Confined granular flow in silos: experimental and numerical investigations

  During confined flow of bulk solids in silos some characteristic phenomena can be created, such as: —         sudden and significant increase of wall stresses, —         different flow patterns, —         formation and propagation of wall and interior shear zones, —         fluctuation of pressures and, —         strong autogenous dynamic effects. These phenomena have not been described or explained in detail yet. The main intention of the experimental and theoretical research presented in this book is to explain the above mentioned phenomena in granular bulk solids and to describe them with numerical FE models verified by experimental results

Investigation of micro-structural phenomena at aggregate level in concretes using DEM

This paper presents numerical analyses of concrete beams under three-point bending. The discrete element methods (DEM) was used to calculate fracture at the aggregate level. Concrete was described as a four-phase material, which was composed of aggregate, cement matrix, interfacial transitional zones (ITZs) and macro-voids. The beam micro-structure was directly taken from our experiments using x-ray micro-tomography. Simulations were carried out with real aggregate modelled as sphere clusters. Numerical results were compared with laboratory outcomes. The special attention was laid on the fracture propagation and some micro-structural phenomena at the aggregate level