Characterization and modelling of ferromagnetic material ageing for reduction of iron losses

CHARACTERIZATION AND MODELLING OF FERROMAGNETIC MATERIAL AGEING FOR REDUCTION OF IRON LOSSES Réf ABG-102066 Sujet de Thèse 04/01/2022 Contrat doctoral Laboratoire d'Electrotechnique et d'Electronique de puissance de Lille Lieu de travail Lille - Les Hauts de France - France Intitulé du sujet Characterization and modelling of ferromagnetic material ageing for reduction of iron losses Champs scientifiques * Matériaux * Energie * Sciences de l’ingénieur Mots clés ferromagnetic material, microstructure, ageing, deformation, iron loss reduction DESCRIPTION DU SUJET CONTEXT In the framework of climate change, the European Union has set key targets to reduce our CO2 emissions, in particular by increasing ENERGY EFFICIENCY. As electric motors consume about 40 % of the electrical energy produced in Europe and considering that, this percentage will inevitably increase in a very near future with the electrification of the mobility, any increase of the efficiency of these motors can potentially lead to major energy savings. In electric motors, about 90 % of the input energy are converted into mechanical work and the remaining part, so-called losses, are dissipated through heat. An increase in the energy efficiency and reliability of electrical machines requires a PREDICTION OF THESE LOSSES especially during the design stage. Up to 30% of these losses occur within the iron core, especially in laminated iron-silicon steel, which plays a key role in energy conversion by facilitating the circulation of electromagnetic fields within electrical machines. The iron loss mechanisms are associated to complex phenomena ranging from the microscopic to the macroscopic scale. Part of these losses are perfectly identified and are predictable from models based on physical properties of the raw materials. The origin of the remaining part of these losses is still poorly known and can represent in some cases up to 50% of iron losses, which is far from negligible. A BETTER UNDERSTANDING OF THE PHYSICAL MECHANISMS THAT GOVERN THE LOSSES, as well as suitable MODELS for predicting their evolution, are required to be able to reduce them. These additional losses are necessarily linked to what the material experiences during the manufacturing and the operation of the electrical machine (stress, temperature, etc.). Numerous works have highlighted the detrimental effects of the manufacturing but few deals with the variation of the iron losses during the operation of the machines. However, recent works have shown that the mechanisms of ageing, so called “magnetic ageing”, may lead to an increase in iron losses of up to 15%. STATE OF THE ART The « MAGNETIC AGEING » refers to the degradation of in-service magnetic properties of Fe-Si steels when submitted to moderate temperature. This phenomenon is due to the PRECIPITATION of carbides or nitrides at low temperatures (less than 200°C), that corresponds to typical operation temperatures of electrical machines. At the microscopic scale, it was determined that precipitates in the range of 100nm to 1μm in size are the most deleterious for magnetic properties and that only Fe-Si alloys with silicon content lower than 3wt% are prone to magnetic ageing. These low grade FE-SI STEELS correspond however to the largest part (73%) of the current market of non-oriented electrical steels, i.e. 9.8 million tons produced in 2019 in the world. In the literature, only scarce attempts have been made to model the precipitation kinetics in this system. However, in the materials science field, many precipitation modelling methods have been developed in the meantime. It appears that models are nowadays available to describe the time evolution of precipitates in magnetic steels. OBJECTIVES We can now expect to construct the BRIDGE BETWEEN MICROSCOPIC MODELS OF PRECIPITATION AND MACROSCOPIC MODELS OF THE MAGNETIC BEHAVIOR in order to be able to predict the “magnetic ageing”. Integrated to the design process, it will enable to better predict the losses leading to more efficient electrical machines and more robust by preventing any overheating. It will also give new opportunities to adapt or develop processes during the manufacturing in order to reduce the ageing effect according to the operation mode of the electrical machine. The aim of the PhD is to develop multi-physical models based on experimental investigations from the microscopic to macroscopic scales of ageing mechanisms in electrical steels and the consequences on the iron losses. DESCRIPTION OF THE WORK The development of the model of magnetic ageing will be based on both theoretical and experimental approaches. The EXPERIMENTAL APPROACH will combine measurements of the magnetic characteristics (B(H) curves, iron losses…) under controlled temperature and strain conditions completed by microstructural characterization by electronic microscopy. It will enable to better understand the mechanism of ageing at both micro and macro levels and to provide data for the identification and validation of the models. Besides, MODELS describing the evaluation of the microstructure will be linked to models of macroscopic behavior of the magnetic material. These microscopic and macroscopic models are already available in the literature, but they are not paired. The most fitted ones according to the experimental results should be chosen and linked together. NATURE DU FINANCEMENT Contrat doctoral PRÉCISIONS SUR LE FINANCEMENT PRÉSENTATION ÉTABLISSEMENT ET LABO D'ACCUEIL Laboratoire d'Electrotechnique et d'Electronique de puissance de Lille This work will be carried out in the frame of the collaboration of two research groups: * the L2EP (http://l2ep.univ-lille.fr/en) having a long experience on the characterization and the modelling of the ferromagnetic material behavior at the macroscopic scale. * the MSMP (https://www.msmp.eu) developing a multidisciplinary research activity in the field of materials and manufacturing processes. The candidate will apply for a doctoral grant from the Doctoral School of Arts&Métiers. SITE WEB : http://l2ep.univ-lille.fr/ INTITULÉ DU DOCTORAT Docteur ParisTech PAYS D'OBTENTION DU DOCTORAT France ETABLISSEMENT DÉLIVRANT LE DOCTORAT Ecole Nationale Supérieure des Arts et Métiers ECOLE DOCTORALE Sciences des Métiers de l'Ingénieur PROFIL DU CANDIDAT The candidate should have either general formation in engineering or in the field of material science. The candidate should be attracted by the exploitation of experimental setups (MEB, magnetic material characterization bench...), by the analysing of physical phenomena at different scales and the developement of models. Date limite de candidature 31/03/2022