Modeling of elasto-plastic behaviour of granular materials using multi-particle finite element simulations

The method of multi-particle finite element involving assemblies of meshed particles interacting through finite-element contact conditions is adopted to study the plastic flow of a granular material with highly deformable elastic-plastic grains. In particular, it is investigated whether the flow rule postulate applies for such materials. Using a spherical stress probing method, the influence of incremental stress on plastic strain increment vectors was assessed for numerical samples compacted along two different loading paths up to different values of relative density. Results show that the numerical samples studied behave reasonnably well according to an associated flow rule, except in the vicinity of the loading point where the influence of the stress increment proves to be very significant. The influence of relative density and initial loading path is discussed

Modeling of elasto-plastic behaviour of granular materials using multi-particle finite element simulations

The method of multi-particle finite element involving assemblies of meshed particles interacting through finite-element contact conditions is adopted to study the plastic flow of a granular material with highly deformable elastic-plastic grains. In particular, it is investigated whether the flow rule postulate applies for such materials. Using a spherical stress probing method, the influence of incremental stress on plastic strain increment vectors was assessed for numerical samples compacted along two different loading paths up to different values of relative density. Results show that the numerical samples studied behave reasonnably well according to an associated flow rule, except in the vicinity of the loading point where the influence of the stress increment proves to be very significant. The influence of relative density and initial loading path is discussed

Influence of particle deformation on the plastic flow of ductile granular materials

A multi-particle finite-element method was proposed to study the elastic-plastic behaviour of ductile powders composed of highly deformable elastic-plastic particles. The focus was put on the study of the uniqueness of the direction of plastic strain increment vectors for a given stress state on the plastic limit, which was assessed using a spherical stress-probing method. Results revealed a non-uniqueness of the direction of plastic flow in a small region of the stress space located in the vicinity of the loading point. The direction of plastic flow was almost unique elsewhere on the plastic limit. The non-uniqueness was explained using a combination of two distinct mechanisms for plastic deformation involving two very different plastic limits

Influence of particle deformation on the plastic flow of ductile granular materials

A multi-particle finite-element method was proposed to study the elastic-plastic behaviour of ductile powders composed of highly deformable elastic-plastic particles. The focus was put on the study of the uniqueness of the direction of plastic strain increment vectors for a given stress state on the plastic limit, which was assessed using a spherical stress-probing method. Results revealed a non-uniqueness of the direction of plastic flow in a small region of the stress space located in the vicinity of the loading point. The direction of plastic flow was almost unique elsewhere on the plastic limit. The non-uniqueness was explained using a combination of two distinct mechanisms for plastic deformation involving two very different plastic limits

Modelling polymeric deformable granular materials - from experimental data to numerical models at the grain scale

Polymeric deformable granular materials are widely used in industry and the understanding and the modelling of their shaping process is a point of interest. This kind of materials often presents a viscoelasticplastic behaviour and the present study promotes a joint approach between numerical simulations and experiments in order to derive the behaviour law of such granular material. The experiment is conducted on a polystyrene powder on which a confining pressure of 7MPa and an axial pressure reaching 30MPa are applied. Between different steps of the in-situ test, the sample is scanned in an X-rays microtomograph in order to know the structure of the material depending on the density. From the tomographic images and by using specific algorithms to improve the images quality, grains are automatically identified, separated and a finite element mesh is generated. The long-term objective of this study is to derive a representative sample directly from the experiments in order to run numerical simulations using a viscoelactic or viscoelastic-plastic constitutive law and compare numerical and experimental results at the particle scale

Numerical modelling of cellulose micro/nanofibril suspensions

International audienc

Numerical modelling of cellulose micro/nanofibril suspensions

International audienc

Numerical modeling of high aspect ratio flexible fibers in inertial flows

International audienceA numerical model for the behavior of flexible fibers under inertial flows was developed by coupling discrete element method and finite volume method. The fibers were discretized into several beam segments, and the equations of motion were integrated with a 2nd order accurate explicit scheme. The 3D Navier-Stokes equations were discretized by a 4th order accurate (space and time) unstructured finite volume scheme. Momentum exchange between the fluid and fibers was enforced by including a source term of the fiber hydrodynamic force in the Navier-Stokes equations. The choice of an appropriate model for the hydrodynamic force on a fiber in a fluid flow depending on the Reynolds number is discussed and covers a range of Reynolds number between 10−2 and 102. The current numerical model is validated against different experimental studies, including deflection of fiber in uniform flow, fibers in isotropic turbulent flow, and concentrated fiber suspension in channel flow. The numerical model was able to reproduce the damping/enhancement phenomena of turbulence in a channel flow as a consequence of the micro-structural evolution of the fibers