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Reference : UMR5312-DAMTEX-001
Workplace : ALBI
Date of publication : Wednesday, December 05, 2018
Scientific Responsible name : Denis DELAGNES and Damien TEXIER
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 21 January 2019
Proportion of work : Full time
Remuneration : 1 768,55 € gross monthly
Description of the thesis topic
Ni-based superalloys are widely used for structural applications at high temperature and intermediate temperature in severe atmospheres. Environment-assisted degradation, i.e. oxidation and corrosion, alters the surface of the materials but also their bulk properties due to a progressive selective consumption of reactive elements involved in the surface degradation process. The material in a shallow region beneath the reactive surface subsequently shows a gradient in chemical composition, microstructure and physical properties. Despite the negligible scale of those gradients (from micrometers to hundreds of micrometers beneath the surface) as compared to the structural component dimensions, the variability of the mechanical behavior within the gradient often drives premature damage and the progressive rupture of the component. To achieve this, the micromechanical characterization of the mechanical properties of the graded materials is substantial, in a large range of temperature.
Due to strong variability in mechanical properties within the graded materials, micromechanical characterization techniques are required. Despite the complexity of micromechanical testing at room temperature (use and data interpretation), the present project aims to measure local properties at high temperatures, temepratures at which surface and sub-surface damage are substantial (up to 800°C for aeronautical turbine applications). "Direct" measurement techniques, providing tensile, creep and fatigue properties using freestanding specimens(few tens of micrometer thick specimens), have the advantage to assess such properties directly usable in numerical models (hypothesis of layer to layer homogeneity). In addition to the macroscopic values measured via these techniques, a specific investigation of the surface for full field kinematic measurements (difital image correlation techniques) would allow local information on deformation and damage mechanisms at the microstructure scale. This in-situ mechanical approach distinguishes itself from conventional techniques, i.e. techniques usually employed in Materials Sciences (hardness testing, nanoindentation, post-mortem observations or after interruptions, etc.) which are not operative anymore for the quantitative evaluation of the gradient of properties.
The present PhD project proposes to tackle the intricate multi-physics dimension of the environment-assisted deformation/damage evaluation by simultaneously correlating the macroscopic/mesoscopic and sub-microstructure/sub-micrometer deformation and the changes in surface reactivity (oxide microcracking, oxide spallation, fast growing oxides, breakaway oxidation, etc.) at high temperature in various atmosphere conditions. The main goal of this in-situ experimental characterization is to bring a novel understanding and a more physical prediction of the local and time-evolving mechanical behavior of graded materials at the microstructure scale related to environmental interactions.
Institut Clément Ader (ICA, CNRS UMR 5312).
ICA is a research laboratory that focuses on the study of structures, systems and mechanical processes. Our activity sectors are in the mechanical industries with a particular focus on aerospace, space, transportation and energy. Our work usually focus on behavior modeling, instrumentation and the study of the durability of the structures or products considered. A large part of our research focus on composite materials, which play today an important role in structures.
ICA has about 80 research professors, 20 temporary researchers, 20 administratives, ingineers and technicians, 90 doctoral students, as well as many students. With the peculiarity of counting:
- Insitutionally, people belonging to four major institutions: UPS and INSA from the Ministry of Higher Education and Research, ISAE from the Ministry of Defence, and Mines Albi from the Ministry of Industry.
- Geographically, staff is distributed in four cities of the Midi-Pyrénées region: Albi, Figeac, Tarbes and Toulouse.
Management is composed of a director and two deputy directors, three ministries are represented in this trio. The technical support team is organized into three components, one for each ministry.
The laboratory is organized into four research groups:
- MSC Group : Composite Materials and Structures
- SUMO Group : Surfaces, Machining, Materials and Tools
- MS2M Group : Modelling of Mechanical Systems and Microsystems
- MICS Group : Metrology, Identification, Control and Monitoring
The present PhD study falls within the research scope of the SUMO group, and more particularly with the research axis: Functional Properties and Microstructural Relationships of of Advanced Materials
The geographical location of the PhD will be on the campus of the IMT-Mines Albi engineering school.
Constraints and risks
High temperature mechanical testing
The present PhD study is part of the ANR-JCJC COMPAACT project: Corrosive-Oxidative coupled Mechanical Performances of materials Assessed via Advanced Characterization Tools
(funded via AAP2018)
The PhD candidate must have experience/knowledge in mechanics of materials: experimental and/or numerical characterization.
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