References of "Kabore, Brice Wendlassida 50024438"
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See detailMicromechanical model for sintering and damage in viscoelastic porous ice and snow. Part I: Model and calibration
Kabore, Brice Wendlassida UL; Peters, Bernhard UL

in International Journal of Solids and Structures (2019)

Ice and snow are usually classified as a viscoelastic or viscoplastic materials according to temperature, strain rate, pressure and time scale. Throughout experimental studies presented in the literature ... [more ▼]

Ice and snow are usually classified as a viscoelastic or viscoplastic materials according to temperature, strain rate, pressure and time scale. Throughout experimental studies presented in the literature, it has been observed that at very low temperatures or high strain rates, porous ice and snow exhibit brittle behavior, but experience high viscous and plastic flow at temperatures close to the melting point and low rates. At the macroscopic level, nonlinearity is not necessarily attributed to permanent changes in the material or yielding but mainly to micro cracks, intergranular sliding, porosity collapse and crack propagation. In this paper, this complex behavior is described with a full microstructure-based model. Classical rheological models and beam theory are used to describe aspects of creep and fracture of granular ice and snow. [less ▲]

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See detailMicromechanical model for sintering and damage in viscoelastic porous ice and snow. Part II: validation
Kabore, Brice Wendlassida UL; Peters, Bernhard UL

in International Journal of Solids and Structures (2019)

The last decades have witnessed sharp progress in both numerical simulation methods and computing power. Realistic simulation of complex structures such as snow remains challenging. The discrete particle ... [more ▼]

The last decades have witnessed sharp progress in both numerical simulation methods and computing power. Realistic simulation of complex structures such as snow remains challenging. The discrete particle approach now accessible due to advances in parallel processing has shown to be a good alternative for brittle and quasi-brittle materials. A novel numerical model has been described in part I of this study. Ice grains in snow are found near their melting points with an enhanced creep that constantly affects its microstructure. The behavior of snow combines characteristics of polycrystalline ice, which depends on stress rate, temperature, hydrostatic pressure and geometrical proprieties that affects its fracture properties. Snow can pass from porous continuous structure to a granular form or creep intensively when loaded. The herein proposed methodology includes time and pressure dependent bonding properties of ice and predicts large displacements, fracture, and granular flow in snow under the effect of mechanical stress. A micromechanical approach based on particle mechanics and beam theory is used to capture microstructure evolution under external loads. The calibration and validation are based on stress-strain data from some compression tests found in the literature. [less ▲]

Detailed reference viewed: 43 (5 UL)
See detailPhase field fracture model for viscoplastic materials in large deformations
Kabore, Brice Wendlassida UL; Loew, Pascal Juergen UL; Peters, Bernhard UL

Scientific Conference (2019, June 13)

Phase-field modeling approach to material fracture and damage has received a growing interest among researchers. It has proven to be an effective way to address crack related discontinuities in continuum ... [more ▼]

Phase-field modeling approach to material fracture and damage has received a growing interest among researchers. It has proven to be an effective way to address crack related discontinuities in continuum mechanics. Also, it solves the problem related to tracking the fracture surface by simply representing the fracture phase with a continuous field variable. Recently, phase-field fracture models have been extended to finite deformations, crack nucleation and applied to complex material behaviors such as plasticity and viscoplasticity. In this contribution we describe a viscoplastic model coupled with a phase-field dynamic fracture model in a large strain formulation. The model include damage, history, rate and temperature dependent behavior. A finite element implementation is presented in a staggered time integration. Moreover, we address the crack closure and crack surfaces interpenetration taking into account tension-compression strength asymmetry. Performance of the model on dynamic crack propagation are presented. [less ▲]

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See detailIntegrated micromechanical model for slope stability analysis
Kabore, Brice Wendlassida UL; Peters, Bernhard UL

Scientific Conference (2019, April 09)

Advances in supercomputing hardware have made it possible to handle highly complex geomechanical analysis with large data. Thus, particle-based methods are gaining an ever-increasing interest with ... [more ▼]

Advances in supercomputing hardware have made it possible to handle highly complex geomechanical analysis with large data. Thus, particle-based methods are gaining an ever-increasing interest with massively parallel programs being developed. These methods have been applied to the analysis of failure mechanisms and scenarios such as mass movement in landslides, avalanches under static, dynamic or seismic loading condition. They provide deep insights into the meso and micro-scale mechanisms leading to macroscopic instabilities. This contribution describes a micromechanical model for stability analysis and simulation in natural or man-made slopes under complex loading and boundary conditions. Based on the micromechanics of loose granular and compacted geomaterial, microstructural change, viscoelastic deformations, fracture, and healing are explicitly integrated into a coupled discrete particle and beam lattice model. Stress-based failure criteria and energy based dissipation and frictional contact are employed. Both gravity increase and strength reduction methods have been employed to evaluate the Factor of Safety (FoS) and potential failure surface and compared. With an emphasis on the impact of the microstructure and its spatial variability on stress-induced microcracks and crack propagation, this study outlines material models and properties relevant to stability analysis. Special focus has been put on layered slopes which present varying shear strength along the depth formed over time according to pressure, temperature, and moisture such as snowpack. This microstructural approach unifies geometrical and material information and allows the structural assembling layers of different strength. [less ▲]

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See detailIdentification of optimal process parameters in selective laser sintering
Kabore, Brice Wendlassida UL; Estupinan Donoso, Alvaro Antonio UL; Peters, Bernhard UL et al

Scientific Conference (2019)

Selective Laser Sintering (SLS) is an efficient method for manufacturing complex geometries with high strength and durability. The SLS process subjects a powder bed to thermal cycles allowing theparticles ... [more ▼]

Selective Laser Sintering (SLS) is an efficient method for manufacturing complex geometries with high strength and durability. The SLS process subjects a powder bed to thermal cycles allowing theparticles to coalesce into a solid part without being completely melted. The thermal cycles along withthe thermo-mechanical properties of the powder dictate the properties of the manufactured part.Choosing optimal parameters that lead to functional parts with the desired stiffness, density andstrength requires extensive testing. Microscales models such that Molecular dynamics and DiscreteParticles offer great flexibilities and capacity to reproduce the SLS process from the physical point ofview [1].This study presents a multi-physical model based on the Extended Discrete Element Method forsimulating the thermodynamics and thermo-mechanics that take place in the SLS process as well asthe microstructure evolution of the part. A thermo-viscoelastic constitutive model for discreteparticles is coupled with heat transfer, sintering and fracture to predict.A genetic algorithm is employed to identify optimal process parameters, namely laser power,scanning speed, preheating temperature and layer thickness in an automated iterative process. Theseparameters are identified so that the density and strength of the cooled part meet the target values. [less ▲]

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See detailSimulation-based Optimisation Of Selective Laser Sintering/Melting Process
Kabore, Brice Wendlassida UL; Peters, Bernhard UL

in Euro PM2019 Congress Proceedings (2019)

In order to adapt Selective Laser Sintering (SLS) and Melting (SLM) to final products and volume production, many scientists have turned to statistical analysis for quality and process stability. Most of ... [more ▼]

In order to adapt Selective Laser Sintering (SLS) and Melting (SLM) to final products and volume production, many scientists have turned to statistical analysis for quality and process stability. Most of which are based on extensive experiments aiming at finding statistical correlations between input parameters such as layer thickness, orientation, scan speed, powder bed temperature, laser power... and resulting strength and residual stress of the manufactured part. However, the rise of computer simulation based on mathematical models allows predictions at a much lower cost. Mathematical modelling of SLS/SLM involves molecular level thermodynamics and thermo-mechanical behaviour of the powder material. In this study, we employ the newly developed Extended Discrete Element Model to reproduce the SLS process including the mechanisms of sintering and the evolution of fracture properties and self-supporting ability. Results show that such microscale model offers high precision and flexibility for finding optimal process parameters. [less ▲]

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See detailMULTI-SCALE MODELLING OF SNOW MECHANICS
Kabore, Brice Wendlassida UL; Peters, Bernhard UL; Willibald, C. et al

in 41st Solid Mechanics Conference (2018, August 27)

Detailed reference viewed: 28 (3 UL)
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See detailMicromechanical model for sintering and damage in viscoelastic porous ice and snow. Part I: Theory
Kabore, Brice Wendlassida UL; Peters, Bernhard UL

E-print/Working paper (2018)

Ice and snow have sometime been classified as a viscoelastic or viscoplastic mate- rial according to temperature, strain rate, pressure and time scale. Throughout experimental studies presented in the ... [more ▼]

Ice and snow have sometime been classified as a viscoelastic or viscoplastic mate- rial according to temperature, strain rate, pressure and time scale. Throughout experimental studies presented in the literature, it has been observed that at very low temperatures or high strain rate, porous ice and snow exhibit brittle behavior, but experience high viscous and plastic flow at temperatures closed to the melting point and low rates. At the macroscopic level nonlinearity is not necessarily attributed to material level permanent changes or yielding but mainly to micro cracks, porosity collapse and crack propagation. This paper attempts to address this complex behavior with a full microstructure based model. [less ▲]

Detailed reference viewed: 31 (3 UL)
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See detailBonded Particle Model for Numerical Analysis of Concrete Fracture under Impact Loading
Kabore, Brice Wendlassida UL; Peters, Bernhard UL

Scientific Conference (2018, July 04)

Linear elastic fracture mechanics and homogenization techniques have shown limitations in concrete fracture analysis due to the existence of localized damage zone and instabilities near the crack region ... [more ▼]

Linear elastic fracture mechanics and homogenization techniques have shown limitations in concrete fracture analysis due to the existence of localized damage zone and instabilities near the crack region. Concrete structures which are primarily quasi-brittle material present rate dependent failure modes, and fracture properties under impact or blast loading. Experiments show that concrete may exhibit viscoplasticity, strain rate and hydrostatic pressure dependent damage and crack propagation. This paper describes an explicit approach of discrete particles bonded with Euler-Bernoulli beams to simulate dynamic fracture in concrete. The fracture is initiated in the beam network and propagated and energy is dissipated according to the prescribed fracture energy. The bonded particle model has shown advanced capability to predict processes including microcracking, crack deflection, bridging and branching occurring in the fracture process zone under impact loading. It can also predict to some extent the crack propagation velocity. A quasi-brittle fracture model with rate dependent strength is elaborated to capture rate dependent behavior at high and moderate strain rates where the concrete exhibit increased load carrying capacity. In order to ensure stability of this program, numerical localnon viscous damping is used. The effect of particle size and bonds in overall response was also investigated. [less ▲]

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See detailMultiscale model of sintering: diffusion and plastic flow
Kabore, Brice Wendlassida UL; Peters, Bernhard UL

Scientific Conference (2017, September 27)

Impacting particles or static aggregated particles at high temperature may undergo a permanent change of shape modifying the microstructure. Two particles in contact can develop some bonds within sub ... [more ▼]

Impacting particles or static aggregated particles at high temperature may undergo a permanent change of shape modifying the microstructure. Two particles in contact can develop some bonds within sub-second time. This fast sintering force in the particular case of the snow contribute to the rheological behavior and grain rearrangement [1]. Understanding the kinetics of sintering in granular material is of great importance in some engineering applications. For decades, diffusional processes have received more attention in investigations related to the mechanisms behind sintering [2]. Some works have suggested that the plastic flow might be neglected in sintering process for stresses are not high enough to cause dislocation. However, some studies have showed that stresses experienced in fine particles necks can be high enough and even lead to plasticity driven sintering. The importance of each mechanism in the sintering process may lie in the temporal and spatial scale of interest. Increasing importance is being accorded to the role of plastic flow in sintering. however, several investigations have proved that the conventional plasticity theory may fail to predict plastic activity at micro-scale, The objective of this work is to develop adequate computational model that includes instantaneous and time-dependent plastic flow at micro-scale. We aim at extending existing models of sintering and plasticity to cope with multiple spatial and temporal scales simulations using Extended Discrete Element Method. The numerical results are compare to experimental data on snow. [less ▲]

Detailed reference viewed: 148 (19 UL)
See detailDynamic Sintering of a High Temperature Granular Material: Experiments and Simulations
Willivald, Carolin; Kabore, Brice Wendlassida UL; Szabó, Denes et al

Scientific Conference (2017, September 26)

Snow changes from a porous solid to a granular material during deformation with high strain rates. This transition occurs in many cases where snow is relevant to engineering problems (vehicle mobility ... [more ▼]

Snow changes from a porous solid to a granular material during deformation with high strain rates. This transition occurs in many cases where snow is relevant to engineering problems (vehicle mobility, avalanche formation and prevention, skiing etc.). For the description of the fast deformation of snow the discrete element method (DEM) is a valuable tool, as it is able to account for both states and the transition between them: the interaction of the loose and bonded particles. For the development of a physically relevant DEM snow model [1] we investigate experimentally along with simulations the basic processes of the granular behavior of snow. In the granular state, sintering plays an important role for the dynamics of the particles. Via sintering the high temperature ice particles (homologous temperature 0.95) bond together and change the structure and the physical properties of the material. This temperature dependent sintering process, which happens in the time range of milliseconds to hours, is in the focus of the present work. The fast sintering of ice in the range of milliseconds has scarcely been investigated. However, from sintering studies with ice cones (radius of 3 mm) we know, that the sintering force is closely related to the contact area of the particles [2]. As the contact area changes considerably for complicated shapes, exhibited by natural snow crystals, we consider different snow types (grain shape and size), besides ice beads as spherical model snow. The latter one is used to exclude shape effects and to directly compare experiments to simulations with spherical particles. To be able to take the effects of the grain shape into account and to examine sintering in the time range of interest (seconds), we perform angle of repose experiments and simulations. Snow is sieved to pile up on a flat base until an angle of equilibrium, the angle of repose, is formed. This angle increases with the sintering of the particles, but also with the inter-particle friction. To analyze the contribution of the friction and the grain shape without sintering, we perform the experiments at a low temperature °C ( 0.87), where sintering can be neglected; thus, the angle of repose is determined by inter-particle friction. With these measurements, we calibrate the simulations. At higher temperatures (up to °C) sintering changes the angle of repose, and a physically relevant sintering law for real snow is established in the simulations. [less ▲]

Detailed reference viewed: 21 (4 UL)