Multi-scale experimental mechanical analysis of localized necking in HCP materials

  • Troyes, Aube
  • CDD
  • Temps-plein
  • Il y a 1 mois
Offer DescriptionThe exponential commercialisation of hexagonal materials, also known as HCP (Hexagonal Close-Packed) materials, is more and more common in several high-tech industries (aeronautics, aerospace, automotive, biomedical, etc.) due to their interesting mechanical and physical characteristics (low density, high strength, high fatigue resistance). Titanium and its alloys in particularare well known for its good thermal and corrosion resistance, as well as for the mechanical properties mentioned above, which explains why these hexagonal materials are increasingly used in many fields, including aerospace and biomedical. For this reason, many scientists and researchers have carried out studies to determine both the mechanical and physical behaviour of HCP materials (especially titanium alloys) using numerical models and experimental techniques. Due to the strong plastic anisotropy at the crystalline scale of hexagonal materials and the presence of the twinning mechanism, the phenomenon of localised necking (localisation), which occurs just before fracture, is quickly initiated. Advanced studies of this localisation phenomenon have become a major challenge for researchers in order to better understand the onset of plastic instabilities. The aim is to minimise the risk of damage and/or failure of the material under study. Thus, the last decade has seen a considerable expansion in virtual numerical simulations to characterise the mechanical and physical behaviour of these materials under different conditions, at high and low temperatures. Nevertheless, the reliability and validity of these numerical approaches must be justified by experimental investigations, even though current analytical or finite-element computation codes are very efficient. For this purpose, several experimental studies based on field methods are being carried out on different types of metallic materials, according to the researchers, in order to better analyse the onset of plastic instability at the time of localisation. Therefore, the propagation of Piobert-Lüders bands and the development of localization during a tensile test were recently treated, at the Laboratory of Mechanical and Material Engineering (LASMIS), by laser interferometry techniques known as ESPI (Electronic Speckle Pattern Interferometry). The main recent results based on this technique are presented by the quantitative identification of the physical characteristics of the localization, such as the width of the bands during a tensile test, their orientation and their maximum strain rate. At the microscopic scale, a source of heterogeneity that cannot be neglected is the twinning phenomenon, and until now, the literature on the influence of twinning on stress bands has been very limited. For this reason, a study using a Scanning Electron Microscope (SEM) by applying the EBSD (Electron Backscatter Diffraction) technique at room temperature and under heat, on specimens subjected to uniaxial tensile tests, followed by a quantitative and qualitative analysis, is expected to provide answers to this problem. The ultimate aim is to better understand the phenomenon of localised necking in order to control plastic instability in hexagonal materials with high plastic anisotropy. The effects of temperature, maximum strain and the imperfections that produce localised necking bands will be analysed in particular. Once developed, the proposed methods can be used to improve and validate current virtual numerical simulations and to optimize hexagonal material forming processes.Funding category: Contrat doctoral
UTT Salary
PHD title: Doctorat en Sciences pour l'Ingénieur, spécialité Optimisation et Sûreté des Systèmes
PHD Country: FranceRequirementsSpecific RequirementsThe candidate's ability to appropriate experimental methods is essential. The proposed thesis is designed for candidates who have completed 5 years of higher education (engineering school or research master's degree) with a solid knowledge of the mechanics of materials (specifically HCP materials) and a strong interest in experimental analysis and numerical simulation.
The candidate should be curious, rigorous and organised. He/she should be able to work autonomously using the experimental equipment and software, and should be able to make suggestions on the experimental tests to be implemented.
The following skills are essential:
- Knowledge of metallic materials
- Knowledge of experimental methods (photomechanics)
- Knowledge of calculation software (Python, Mathematica, etc.) and finite element method calculations
- Communication skills, particularly with different people and different professions (materials, processes, physics, optics, chemistry, optics, etc.).The following skills will be highly valued:
- Carrying out in-situ tensile tests using a scanning electron microscope.
- Experience in image correlation
- Experience in processing experimental datacapacité du candidat à s'approprier les méthodes expérimentales est essentielle. Le sujet de thèse proposé s'adresse aux candidats de formation Bac +5 (école d'ingénieur ou master recherche) avec de solides connaissances en mécanique des matériaux (spécifiquement les matériaux à structures cristallographiques hexagonales) et un gout prononcé pour l'analyse expérimentale et la simulation numérique.
Le/la candidat(e) devra être curieux(se), rigoureux(se) et organisé(e). Il/elle devra être autonome rapidement sur les équipements expérimentaux et les logiciels et il/elle sera force de proposition sur les tests à mettre en œuvre et les méthodologies à employer.
Les compétences ci-dessous sont indispensables :
  • Connaissance sur les matériaux métalliques
  • Connaissance des méthodes expérimentales (La photomécanique)
  • Connaissance des logiciels de calcul (Python, Mathématica,...) et de calcul par élements finies
  • Capacité de synthèse et d'exploitation des données matériaux disponibles
  • Capacités de communication, notamment avec différents intervenants et différents métiers (matériaux, procédés, physique, optique, chimie, optique…)
Les compétences suivantes seront fortement appréciées :
  • Réalisation d'essais de traction in-situ dans un microscope électronique à balayage.
  • Expérience sur la corrélation d'images
  • Expérience en traitement des données expérimentales
Additional InformationWork Location(s)Number of offers available 1 Company/Institute Université de Technologie de Troyes Country France City Troyes GeofieldWhere to apply WebsiteContact WebsiteSTATUS: EXPIRED

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