Taking in consideration different length scales,digital microstructures are to embed in a FE-net and to analyze withregard to local stresses and strains. The micromechanical analysisdeveloped for two-dimensional microstructures is possibly to extend tothree-dimensional microstructures. For this it is of interest todetermine a sufficiently small microstructural window that can serve asan RVE for simulation of micromechanical response of theseheterogeneous Mg-alloys.

The existing model for convection drying, which includes heat and masstransfer, involves many effective parameters which must be known beforedrying kinetics can be predicted. The possibility to compute theseparameters from simulated pore networks shall be investigated. In asecond step, the model shall be extended to account for mechanicalstress and deformations or even cracks due to gradients in temperatureand moisture content.

For drying of thermosensitive granular products, such asbiomaterials,these may be mixed with particulate adsorbent materials,e.g. zeolites. For this process, heat and mass transfer shall besimulated by discrete element modelling. For model testing, existingexperimental results may be used. Pure heat or pure mass transfer arelimiting cases of the problem.

The micro structure of polycrystalline materials has a strong influenceon many materials properties, like strength and toughness. Therefore itis important to control the temporal evolution of grain structures inorder to optimise material properties in processings.
Grain growth and recrystallization have become a large topic ofresearch and publishing over recent years. Experiments, simulationsused as computer experiments and theories have been developed. The aimof simulations and experiments is to model the micro structuralevolution of polycrystalline materials under realistic conditions. Onemethod to simulate grain growth is the Monte Carlo simulation based ona numerical realization of the Potts model. This model representscurvature driven grain growth and takes the interaction of grains intoconsideration. Especially the last years opened up growingpossibilities of investigations of 3D grain growth with the help ofcomputer simulations.
The aim of the present project is to simulate grain growth andrecrystallization of monophase or twophase structures especially afterlarge deformation, with the second phase particles being either staticor dynamic and with orientations and anisotropy.

The agglomeration of particles is a process in which particles collideand stick together to form new larger particles. This process isdescribed by population balance equations for a time dependent particlesize distribution function. The decisive quantities determining theprocess are integral kernels describing the collision frequency andintensity, adhesion probability and agglomeration rate.
It is practically observed that particles agglomerate at highfrequencies and the project aims to identify the mechanisms leading tothese agglomeration rates. The process will be simulated using thediscrete element method in order to determine agglomeration kernels.The project could carried out as thesis work in process engineering andnumerical mathematics. The latter would involve next to simulations ananalysis of the discrete element method.

In the first period the particle interactions withinterstitial pore fluid were ignored in the contact model of stiffparticles with stiff to soft contacts. With respect to moist granulatesthe influence of liquid bridge bonds, i.e. the viscous behaviour atcontact detachment for granulates formation and breakage has to beconsidered in the 2D simulations of discrete element method (DEM).Linear kinetics of drying and wetting rates are assumed for the singlemicroscopic contact of primary particles inside of the granule. Usingthis, the macroscopic behaviour of a fluidized bed is simulated. Thesesimulations are experimentally calibrated by an impact tester.

Simulation der Bruchdynamik feuchter Granulate

In der ersten Förderperiode wurden die Partikelwechselwirkungen mitdem umgebenden Porenfluid im Kontaktmodell steife Partikel mit steifenbis nachgiebigen Kontakten ignoriert. Im Falle feuchter Granulate mussjedoch der Einfluss von Flussigkeitsbruckenbindungen, d.h. das viskoseVerhalten, sowohl für die Granulatbildung als auch für denGranulatzerfall in den 2D-Simulationen mit Hilfe derDiskreten-Elemente-Methode (DEM) berücksichtigt werden. Es wird einelineare Kinetik der Trocknungs- und der Befeuchtungsgeschwindigkeiteines einzelnen mikroskopischen Primärpartikelkontaktes innerhalb desGranulatkornes angenommen. Damit wird das makroskopische Verhalteneiner bewegten Wirbelschicht simuliert. Diese Simulationen werden durchExperimente an einer Prallapparatur kalibriert.

The previous contact models should be supplemented for compliant particles with soft contacts(e.g. multi-layer granulates). The two dimensional algebraicforce-displacement models for normal and tangential forces are extendedto describe completely the three dimensional stress and strain state ofboth hemi-spaces of the contact. Besides the contact deformation thecomplete deformation of the compliant particle is to be considered aswell. A 3D-model of elasto-viscoplastic particle behaviour should bederived which includes energy dissipation and adhesion.

Modellierung des Kontaktverhaltens nachgiebiger Partikel und Simulation der Bruchdynamik der Granulate

Die bisher entwickelten Kontaktmodelle sollen für nachgiebige Partikel mit nachgiebigem Kontaktverhalten (bspw. mehrschichtige Granulate) erweitert werden. Dazu ist esnotwendig, die algebraischen zweidimensionalen Kraft-Weg-Modelle fürNormal- und Tangentialkräfte um eine vollständige Beschreibung desdreidimensionalen Spannungs- und Dehnungszustandes in den beidenHalbräumen eines Kontaktes zu ergänzen. Neben der Kontaktdeformationist auch die Volumendeformation der nachgiebigen Partikel zuberücksichtigen. Es soll ein 3D-Modell für elasto-viskoplastischesPartikelverhalten mit Energiedissipation und Haftung entwickelt werden.