09:00 am
Micro-mechanical modelling of heterogenous materials containing microcracks with discrete element method
Prof. Dr. Marc Huger | IRCER / University of Limoges | France
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Authors:
Quentin Pledel | IRCER / University of Limoges | France
Prof. Dr. Marc Huger | IRCER / University of Limoges | France
Prof. Dr. Damien André | IRCER / University of Limoges | France
Refractories are ceramic materials resistant to very high temperatures. Used in environments with harsh solicitations, a better understanding between the macroscopic physical properties and the micro-structural aspects is necessary to optimize their use. This work proposes to focus on the resistance to thermal shocks by micro-mechanical modelling.
To do this, numerical simulations are performed to model the microcracking caused by the thermal expansion mismatch between the constituents and its influence on the non-linear stress-strain behavior of such materials. The work has been performed with GranOO, a soft-ware using the discrete element method (DEM), to which is added a periodic homogenization method to consider the phenomena at microscopic scale on the macroscopic properties. The damage process is studied during the cooling of refractories materials in order to reproduce a multi-cracked state and to understand the mechanisms depending on parameters such as the proportion of the constituents, their thermal expansion anisotropies and the geometry of the model. From these simulations, the main macroscopic mechanical properties involved in the resistance to thermal shocks can be analyzed and related to the microcracking state of the sys-tem. These results are then compared with analytical models and experimental results. These developments allow a better understanding between microstructure and macroscopic behavior. This work envisages the potential of the discrete element method to predict the thermome-chanical behavior of microcracked media.
Keywords: Refractories, Microcracks, DEM modelling, Thermal shock, Periodic homogenisation.
09:20 am
Development of an orthotropic elastic-visco-plastic behaviour law for the thermomechanical modelling of refractory masonries
Prof. Alain Gasser | University of Orléans | France
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Authors:
Zakariae El-Alami | University of Orléans | France
Dr. Thomas Sayet | University of Orléans | France
Prof. Alain Gasser | University of Orléans | France
Some refractory linings that protect metallic vessels from the hot temperature of the products they contain are made of masonries with dry joints (i.e. without mortar). The presence of these joints makes the behaviour of the masonry non-linear and orthotropic, allowing a free expansion during the first part of the temperature increase, reducing the stresses in the masonries. Since bricks have an elastic-visco-plastic behaviour at high temperature, it is necessary to develop an orthotropic elastic-visco-plastic behaviour law for the homogeneous material that has a behaviour equivalent to that of the brick and dry joint assembly. This non-linear behaviour is the origin of creep, that could be represented at the microscopic scale (brick scale) by the well-known Norton-Bailey creep law. This law was in a previous study adapted to the macroscopic scale (masonry scale) for orthotropic secondary creep (with a constant creep strain rate). This study presents the adaptation of this law to primary creep for which the strain rate is not constant. The parameters of this new law are determined by a non-linear full-field homogenization technique. The identified law is then validated by comparing the results obtained by micro-modelling (bricks and joints are simulated) and macro-modelling (bricks and joints are replaced by the equivalent material) of an elementary periodic cell subjected to different loads.
09:40 am
FE modelling of refractories’ material properties based on 3D microstructural analysis
Dr. Simon Pirkelmann | Fraunhofer ISC, Zentrum HTL Bayreuth | Germany
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Authors:
Dr. Simon Pirkelmann | Fraunhofer ISC, Zentrum HTL Bayreuth | Germany
Dr. Gerhard Seifert | Fraunhofer ISC, Zentrum HTL Bayreuth | Germany
Dr. Holger Friedrich | Fraunhofer ISC, Zentrum HTL Bayreuth | Germany
Prof. Dr. Friedrich Raether | Fraunhofer ISC, Zentrum HTL Bayreuth | Germany
The common goal to achieve climate neutrality implies that thermal processes must be quickly optimized with respect to energy and material efficiency. Refractories can contribute doubly to these goals, by improved functionality and increased service life in the process they were designed for as well as by minimizing the energy needed for their production. Simulation-based methods can help to significantly reduce the time and experimental effort for systematic development of refractory materials towards more sustainability.
We present a simulation-based approach to evaluate the influence of material composition on the mechanical strength of refractory materials. The method aims to identify the most critical structural elements with regard to component failure under various loads, which must be avoided to improve reliability of new refractory materials.
In this approach, a neural network is trained and applied for image segmentation of 3D computed tomography images of refractory samples. The network can distinguish different components of the material such as pores, coarse-grained inclusions and fine-grained matrix. This information is used to generate a voxel-based volumetric model, from which structural properties such as phase fractions, porosity, grain sizes as well as their spatial distributions are extracted. By converting these into a mesh geometry, finite element analyses of the influence of different thermal and mechanical load cases on the material are done.
By performing these simulations for different material types and a variety of specimens, it becomes possible to evaluate the relationship between the identified structural properties of a specimen and assess the resulting probability of failure.
10:00 am
Multiscale modeling of gas-slag-refractory interactions and degradation mechanisms
Prof. Anssi Laukkanen | VTT Technical Research Centre of Finland Ltd | Finland
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Authors:
Prof. Anssi Laukkanen | VTT Technical Research Centre of Finland Ltd | Finland
Tom Andersson | Finland
Matti Lindroos | Finland
Prof. Elina Huttunen-Saarivirta | Finland
Dr. Eetu-Pekka Heikkinen | University of Oulu | Finland
Riku Mattila | University of Oulu | Finland
Assoc. Prof. Ville-Valtteri Visuri | University of Oulu | Finland
Dr. Mari Lindgren | Metso Outotec | Finland
Refractories interacting with molten slags and gaseous process environments can be unexpectedly compromised with respect to their durability and display complex failure modes. We focus particularly on degradation mechanisms resulting in catastrophic refractory tile failure due to formation of multiple reaction zones and chemical reactivity taking place within its respective microstructure. In order to address this complex micromechanism, we propose and demonstrate a multiscale modeling approach which accounts for the various mechanistic couplings between the material and the operating environment at the scale of the material microstructure. Focus of the work is in full field representation of material microstructure seen critical in order to be able to reproduce the observed failure mechanisms computationally. The approach is benchmarked against thermodynamical and kinetical dissolution and chemical wear models. Use case work with tiles seen use in flash smelting operation is presented and the findings are compared to experimental and characterization results. The results are discussed with respect to properties and characteristics of refractories critical for their performance in complex multiphysical operating environments. The work demonstrates how formulating the refractory degradation as a multiscale one yields improved ability to evaluate performance against challenging durability and lifetime limiting process conditions.