Coraline Chartier, awarded at the AFPM Conference

7 June 2022

Congratulations to Coraline Chartier, 3rd year PhD student.

Her PhD work was awarded the 2nd poster prize at the AFPM 2022 International Conference. She presented her advances on wound dressing applications using chitosan aerogels and cryogels: Release of ascorbic acid 2-phosphate and dexamethasone phosphate from chitosan aerogels and cryogels in view of potential wound dressing applications.

The "Advanced Functional Polymers for Medicine" conference was held in Sophia Antipolis from June 1 to 3. The 2022 edition was organized by Sytze Buwalda and Tatiana Budtova from the BIO team.

Coraline Chartier's PhD is co-directed with the Max Mousseron Institute of Biomolecules of the University of Montpellier (Benjamin Nottelet and Hélène Van Den Berghe).

Coraline has already been awarded for her work at the 4th EPNOE Junior Scientist Meeting (Poster Award 2021).

PhD defence of Ahmed Mehdi Roula

20 May 2022

Ahmed Mehdi Roula defends his PhD in Computational Mechanics and Materials on May 20th, 22

"Towards a better control of geometries produced by sheet forming process."

Ahmed Mehdi Roula conducted his PhD work in the CSM team. He defends his PhD in Computational Mechanics and Materials on May 20th, 2022 in front of the following jury:

– Prof. Pascale Balland, Université Savoie Mont Blanc

– Prof. Carl Labergere, UTT

– Prof. Régis Bigot, ENSAM Metz

– Prof. Katia Mocellin, Mines Paris

– Prof. Pierre-Olivier Bouchard, Mines Paris

Abstract:

The present Ph.D. thesis deals with the sheet flow forming process. This forming process enables to reach large plastic strains due to the compressive and incremental action of the roller. Nevertheless, the lack of geometric accuracy of the produced parts represents a major issue of the process and the main motivation of the present work. The first step was to set up a numerical model of the flow forming process using the finite element software FORGE®. Multiple appropriate mechanical characterization tests associated with constitutive models adapted to the process conditions enabled to enhance the material behavior description during the process modeling. In a second step, a finite element analysis using the numerical model allowed understanding the complex material flow during the forming operation. This led to the explanation of defects presence. Finally, practical developments were established in order to control the flow formed geometries within a wide range of reduction ratios. A finite element analysis was also conducted to predict the fracture limit of the studied material for the flow forming process.

Keywords: Sheet flow forming, necking, mechanical characterization, finite element modeling, incremental processes

Phd defence of Ichrak Rahmoun

19 May 2022

Ichrak Rahmoun defends her PhD in Computational Mechanics and Materials on May 19th, 22

Thermomechanical modelling of photovoltaic module manufacturing processes

Ichrak Rahmoun conducted her PhD work in the CSM team. She defends her PhD in Computational Mechanics and Materials on May 19th, 2022 in front of the following jury:

– Prof. Veronica Bermudez, Qatar Environment and Energy Research Institute

– Prof. Cyrille Sollogoub, CNAM

– Prof. Corinne Alonso, Université de Toulouse Paul Sabatier III

– Prof. Fabrice Schmidt, Mines Albi

– Prof. Jean-Luc Bouvard, Mines Paris

– Prof. Pierre-Olivier Bouchard, Mines Paris

– IR Aude Derrier, CEA Liten

Abstract:

Photovoltaic (PV) modules consist of active photovoltaic layers (Silicon, passivation), protective encapsulation layers (polymers) and glass plates. The performance and service life of PV modules depends on their ability to withstand various environmental constraints related to thermomechanical, physical, chemical and / or electrical phenomena. In the context of this work, we will focus on the residual stresses induced during manufacturing. This comprises the electrical interconnection between the PV module cells, by welding or adhesive bonding of conductive lines, and the protective encapsulation by layers of polymers and glasses using lamination process (hot pressing). The induced residual stresses can be at the origin of failures observed on the modules (delamination, cell cracking, breakage of interconnections …etc.), either at the manufacturing stage or during the lifetime of the modules due to the service constraints. The objective of this PhD thesis will be to model the encapsulation and interconnection processes of cells to better understand their influence on the main failures observed on the modules.

Keywords: Photovoltaic module, lamination process, interconnection process, thermomechanical modelling, residual stresses

PhD defence of Marie-Anne Vidal

7 April 2022

Marie-Anne Vidal defends her PhD in Computational Mechanics and Materials on May 4th, 22

Study of backward flow forming of tubes: development of an experimental and numerical analysis protocol

Marie-Anne Vidal conducted her PhD work in the CSM team, under the supervision of Katia Mocellin and Pierre-Olivier Bouchard. She defends her PhD in Computational Mechanics and Materials on May 4th, 2022 in front of the following jury:

– Tudor Balan ENSAM Metz

– Sébastien Thibaud, ENSMM Besançon

– Elisabeth Massoni, Mines Paris CEMEF

– Laurent Dubar, Université polytechnique des Hauts de France

– Dorian Depriester, ENSAM Aix en Provence

– François Frascati, MBDA

Abstract:

Flow forming is an incremental forming process producing thin tubes without any material loss and with enhanced material characteristics due to strain hardening. The objectives of this work are a part of MBDA’s approach to develop a study protocol on aluminum 6061 alloy in order to predict damage occurrence during the metal forming operation, and then to apply this protocol on a high performances material (HPM).

First, experimental flow forming campaigns were conducted on both MBDA device and lab-scaled device Fluoti at CEMEF in order to determine the influence of process parameters on flow formability (speeds, reduction ratio, initial thickness, number of passes…). Behavior characterization of the aluminum 6061 alloy was performed using compression, tension and torsion tests so that parameters of a behavior law could be identified and thus be integrated into FORGE® software for flow forming modelling.

The simulation set-up in FORGE® is crucial to find a compromise between long simulation duration and result precision. Those results of flow forming simulations (final tube geometry, loads on tools, fracture occurrence) were then compared to corresponding experimental configurations. The comparison showed good correlation between the geometries but a discrepancy on the efforts was found. The damage fracture criteria used were based on the first principal stress (Latham and Cockcroft), the first and the second principal stresses (McClintock), the stress triaxiality (Oyane) and the maximum shear.

Finally, the protocol was simplified based on the results on the aluminum 6061 alloy and transposed on the HPM to test its limits. Although no fracture occurred during the flow forming campaign on this material, the loads on the tools and the final tube geometries showed good agreement.

Keywords: damage, modelling, behaviour, flow forming

PhD defence of Charles Brissot

14 April 2022

Charles Brissot defends his PhD in Computational Mechanics and Materials on April 14th, 22

Numerical and experimental study of boiling flows – Application to quenching

Charles Brissot conducted his PhD work in the CFL team, under the supervision of Elie Hachem and Rudy Valette in the framework of the ANR Industrial Chair INFINITY. Charles defends his PhD in Computational Mechanics and Materials on April 14th, 2022 in front of the following jury:

Prof. ABISSET-CHAVANNE Emmanuelle, Arts et Métiers ParisTech, referee

Prof. COUTINHO Alvaro, Federal University of Rio de Janeiro, Brésil, referee

Dr. LAJOINIE Guillaume, University of Twente, examinateur,

Prof. ARGENTIN Médéric, Institut de Physique de Nice, examinateur

Mr. EVEN David, Faurecia, invité

Abstract:

Boiling is an efficient way of extracting heat from a solid. It is used in many industrial processes among which quenching. Quenching consists in the rapid cooling of a metallic part inside a fluid in order to improve the material properties of the microstructure. The control of the temperature variations is of great importance in this process. Thus, the understanding of boiling is fundamental as it drives the cooling rate.

This thesis is part of the industrial Chair INFinity that gathers a consortium of twelve companies. They share a common will to improve their knowledge on quenching thanks to numerical simulation. Computational Fluid Dynamics (CFD) is a solution to reduce the number of full scale experiments for every new quenched part, as well as to provide a powerful tool describing the underlying physics. We thus aimed at developing a tool to simulate the quenching process at an industrial scale. To do so, different aspects have be studied: (i) analyse the most important features of boiling to simplify the problem, (ii) implement a numerical Finite Element framework to properly simulate multiphase systems with phase change, (iii) challenge the model with the simulation of film boiling on a sphere quenching experiment and on a vertical film boiling benchmark and (iv) enrich the model to account for all boiling modes and to implement a quenching model that can handle industrial applications.

An analytical work on the mass, momentum and energy conservation equations in the context of quenching is proposed. A numerical work is tackled to develop a tool based on a Level Set framework and a Continuous Surface Force approach. Validations are then done on 2D and 3D benchmarks of increasing complexities. An experimental work on the quenching of mall nickel spheres has been done. Validations on academic and industrial benchmarks with discussion on the assumptions and the validity of the model are presented.

Keywords: Boiling, Quenching process, Phase Change, Vaporisation, Finite Element Method, Level Set method

PhD Defence of Brayan Murgas Portilla

Brayan Murgas Portilla defends his PhD in Computational Mechanics and Materials on April 7th, 22

20 March 2022

Towards a precise description of the grain boundary mobility and energy for their numerical integration in finite element modeling of recrystallization and grain growth mechanisms.

Brayan Murgas Portilla conducted his PhD work in the MSR team, under the supervision of Nathalie Bozzolo and Marc Bernacki. Brayan defends his PhD in Computational Mechanics and Materials on April 7th, 2022 in front of the following jury:

– Prof. Laurent Delannay, Université catholique de Louvain, Belgium

– Prof. Lukasz Madej, AGH University, Poland

– Prof. Roland Logé, EPFL, Switzerland

– Prof. Somnath Ghosh, Johns Hopkins University, USA

– Prof. Carl Krill, Ulm University, Germany

– Dr. Baptiste Flipon, MINES ParisTech, France

– Dr. Pascal de Micheli, TRANSVALOR, France,

Abstract:

The relation among process, microstructure, properties, and performance of materials is of great interest to the metal forming industries. The microstructure-properties relationship has opened an exciting branch of materials science called Grain Boundary Engineering: control the grain boundary character distribution to promote specific materials properties. The manufacturing process of metals can be modeled at the mesoscopic scale using numerical tools that describe the evolution of grain boundaries. The Level-Set (LS) approach in the context of Finite Element (FE) formulations remains a powerful tool that allows mimicking industrial thermomechanical treatments where large deformation can take place.

This work aims to improve the FE-LS framework by including enriched grain boundary energy and mobility models and applies the enriched framework to the simulation of grain growth and recrystallization in a single phase austenitic steel. Accounting for the heterogeneity or the anisotropy of GB properties is necessary if special boundaries or subgrains have to be considered. The improvement of the GB property models was incorporated in different FE-LS formulations using additional terms in the existing kinetic framework. Noteworthily, the current knowledge of GB property data and models still suffers from the lack of relevant and accurate experimental data. The complete description of GB properties calls for high spatial three-dimensional microstructure analysis, and for temporal evolution under given thermomechanical conditions, which remains unattainable with the state-of-the-art techniques.

Based on partial experimental data acquired in this work, existing molecular dynamics data, triple junction test cases and polycrystalline simulations, it was confirmed that the Anisotropic formulation was the most physical formulation. Nevertheless, when low levels of heterogeneity/anisotropy are involved in the considered microstructure, the isotropic formulation can be used safely in grain growth and recrystallization simulations. Finally, the new proposed numerical framework is shown to be able to model coherent and incoherent twin boundaries individually or immersed in a polycrystalline microstructure.

Grain growth simulation in an austenitic steel at 900°C using EBSD data

Keywords: Finite Element Method, Level-Set, Grain Boundary, Grain Boundary Mobility, Grain Boundary Energy, Anisotropy