Investigations of quasi-static vortex-structures in 3D sand specimens based on DEM and Helmholtz-Hodge vector field decomposition

The paper presents some three-dimensional simulation results of granular vortex-structures in cohesionless initially dense sand during quasi-static plane strain compression. The sand behaviour was simulated using the discrete element method (DEM). Sand grains were modelled by spheres with contact moments to approximately capture the irregular grain shape. The Helmholtz-Hodge decomposition (HHD) of the displacement vector field from DEM calculations was used. The variational discrete multiscale vector field decomposition allowed for separating a vector field into the sum of three uniquely defined components: curl free, divergence free and harmonic. Vortex-structures were strongly connected to shear localization. They slightly changed along the specimen depth. They localized in locations where shear zones ultimately developed

Experimental and numerical investigations of concrete behaviour at meso-level during quasi-static splitting tension

The paper describes experimental and numerical results of quasi-static splitting tensile tests on concrete specimens at meso-scale level. The loading strip was made of plywood or steel. Fracture in concrete was detected at the aggregate level by means of three nondestructive methods: 3D x-ray micro-computed tomography, 2D scanning electron microscope and manual 2D digital microscope. The discrete element method was used to directly simulate experiments at the meso-scale. Concrete was modelled as a random heterogeneous 4-phase material composed of aggregate particles, cement matrix, interfacial transitional zones and macro-voids based on micro-tomographic images. Two-dimensional calculations with real concrete microstructure were carried out. A satisfactory agreement between numerical and experimental results was achieved. The evolution of contact normal forces, coordination number, broken contacts, grain rotations and crack displacements was also investigated. In addition, each energy component was calculated and analyzed at a different stress-displacement stage

Numerical simulations of sand behaviour using DEM with two different descriptions of grain roughness

A quasi-static homogeneous drained triaxial compression test on cohesionless sand under constant lateral pressure was simulated using a three-dimensional DEM model. Grain roughness was modelled by two different approaches: first with contact moments applied to rigid spheres and second with clusters of rigid spheres imitating irregular particle shapes. The effect of the grain roughness (shape) on shear strength, dilatancy, energy and dissipation was analyzed using both models. Numerical results were directly compared with experimental results on Karlsruhe sand

Modelling of behaviour of plain concrete using DEM

For a realistic description of the mechanical behaviour of concrete, which is a strongly inhomogeneous and non-linear, microstructure should be taken into account. The size, volume and shape of aggregate have a pronounced influence on the concrete behaviour at the macro-level. In this paper, the discrete element method (DEM) is used as a tool to describe the concrete behaviour under uniaxial compression and uniaxial tension

Modelling of concrete fracture at aggregate level using dem based on X-ray CT images of internal structure

The paper describes two-dimensional meso-scale numerical results of fracture in notched concrete beams under quasi-static three-point bending. Concrete was modelled as a random heterogeneous 4-phase material composed of aggregate particles, cement matrix, interfacial transitional zones (ITZs) and air voids. As a numerical approach, the discrete element method (DEM) was used. The concrete micro-structure in calculations was directly taken from real concrete specimens based on 3D x-ray micro-computed tomography images and 2D images by the scanning electron microscope (SEM). Attention was paid to the shape of a fracture zone between aggregate grains. In addition, the effect of properties of ITZs on fracture was studied

Investigations of micro-structure evolution in granular shear zones using DEM

The evolution of shear zones in initially medium dense cohesionless sand for quasistatic 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 laid on some micro-structural events appearing in shear zones (force chains, vortex structures, local density fluctuations). The calculated geometry of shear zones was compared with experimental results of laboratory model tests and finite element calculations

Simulations of fracture in concrete beams under bending using a continuum and discrete approach

The paper describes two-dimensional meso-scale results of fracture in notched concrete beams under bending. Concrete was modelled as a random heterogeneous 4-phase material composed of aggregate particles, cement matrix, interfacial transitional zones and air voids. Within continuum mechanics, the simulations were carried out with the finite element method based on a isotropic damage constitutive model enhanced by a characteristic length of micro-structure. In addition, the discrete element method was used. The concrete micro- structure in calculations was directly taken from real concrete specimens based on 3D x-ray micro-computed tomography images and 2D images by the scanning electron microscope. ovides information and instructions for preparing a Full Paper to be included in the Proceedings of COMPLAS XIII Conference

Rolling Friction in Loose Media and its Role in Mechanics Problems

Rolling friction between particles is to be set in problems of granular material mechanics alongside with sliding friction. A classical problem of material passive lateral pressure on the retaining wall is submitted as a case in point. 3D method of discrete elements was employed for numerical analysis. Material is a universe of spherical particles with specified size distribution. Viscose-elastic properties of the material and surface friction are included, when choosing contact forces. Particles' resistance to rolling relative to other particles and to the boundary is set into the model. Kinetic patterns of medium deformations are given. It has been proved that rolling friction can significantly affect magnitude and nature of passive lateral pressure on the retaining wall

Traceability of raw materials in silos in an anode plant

Carbon anodes, regularly consumed in primary aluminum production, are made of calcined petroleum coke, coal tar pitch, and recycled materials. The properties of calcined coke depend on the source of crude oil and the calcination conditions. Similarly, pitch properties depend on the coal tar source and the manufacturing process. Different calcined coke and pitch mixtures are commonly used in anode manufacturing to meet various regulations and/or due to economics and availability. This makes it hard to maintain the anode quality. Calcined coke and pitch are placed in silos and used when required for production. It is hard for the industries to track the source of raw materials used in their daily recipes. This article presents an approach to trace back the details of the use of particulate raw materials with a custom-made software, which takes into account the type (mass flow or funnel flow) of silos. Such tracking can help identify the causes of problems and maintain/improve anode quality