Missions

In polycrystalline metallic materials, quantitative and statistical evaluation of plastic activity in relation to microstructural parameters (grain size, phases, precipitation state, etc.) and environmental conditions (high temperature, oxidizing atmosphere, etc.) is essential for understanding deformation mechanisms in relation to mechanical stresses and stress paths. Plastic deformation is often localized in the form of bands within the grains, called slip bands, which appear and persist during loading, reflecting the collective movement of dislocations. These bands of plastic deformation localization and their evolution as a function of microstructure during material deformation are likely to be the source of damage. It is therefore necessary to be able to accurately map the location of deformation within polycrystalline aggregates in order to identify critical configurations that can lead to crack initiation and to understand the factors that cause these deformation mechanisms.

Various experimental techniques are now available for measuring deformation fields and determining the location of plasticity. These techniques generally require the use of high-resolution imaging systems, such as scanning electron microscopy (SEM), laser scanning confocal microscopy (LSCM), atomic force microscopy (AFM), etc. The combined use of SEM and digital image correlation (DIC) is often used and described as an effective approach for the experimental determination of deformation fields at the microstructure scale. The principle is based on measuring the displacement field of the surface of a sample subjected to a load from two images acquired at two distinct load times (usually an undeformed reference state and a deformed state). The use of a speckle pattern is generally necessary to track the same area of interest between the two states considered. By deriving the displacement fields, this technique then allows the continuous deformation fields in the polycrystalline aggregate to be extracted. It is thus possible to observe slip bands, localized in the form of discontinuous traces on the surface of deformed metals.

In addition, EBSD (Electron BackScatter Diffraction) is a crystallographic analysis technique also used in conjunction with SEM to obtain information on the local orientation of the crystal lattice and, consequently, a range of information on the microstructure: grain size and morphology, grain boundaries, misorientations between neighboring grains or within the grain core if the sample has been deformed. High-resolution EBSD analyses also allow us to observe slip bands, micro-rotation, and elastic deformation, as a complementary analysis to the HR-DIC technique.

Since most of these characterization techniques are performed under different conditions and generate data of different formats and sizes for the same sample observed, various code bases (Matlab, Python, commercial analysis software) are used for post-processing and analysis of each type of data. To date, there is no unified method for the automated and correlative processing of these multimodal data (i.e., data from different experimental techniques). However, identifying the parameters of crystalline plasticity models is essential for understanding and predicting the heterogeneous behavior of alloys, particularly titanium alloys, at the microscopic scale. Therefore, the objective of this project will be to assimilate data and identify descriptive parameters of crystalline plasticity to enable the simulation of crystalline plasticity of corresponding 3D aggregates.

Activities

The objective of the project is to move towards the implementation of a unified analysis chain dedicated to the post-processing of characterization data (in this case DIC and EBSD) for a metallic material. To do this, the candidate must be able to implement these characterization techniques on samples subjected to mechanical stress in terms of traction, fatigue, and creep, post-process the data obtained, and develop scripts (Python) to automate the fusion and analysis in order to qualify and quantify the deformation mechanisms of the metal alloy being studied. The material studied will be a titanium alloy microalloyed with oxygen. A titanium alloy with an oxygen concentration gradient will also be used in the application. Beyond the experimental characterization of plasticity at the microstructure level, the transfer to a numerical model will be of interest in order to predict the behavior and mechanical integrity of titanium alloys for structural applications subjected to oxidizing atmospheres.

This exploratory project will interact with the thesis work currently underway at the ICA laboratory as part of the ERC-SG HT-S4DefOx project. The candidate will be welcomed into the laboratory, where they will be able to interact with PhD students and permanent members of the research team. In particular, the candidate will be involved in mechanical testing with optical/electronic tracking for digital image correlation, thereby generating the data necessary for the project. Full-field experimental data assimilation (DIC) will also enable the digital twin of the polycrystalline aggregates studied.

Skills

- keen interest in materials science (metallic materials)
- enjoy working with materials: perform tensile tests, use characterization tools
- knowledge of the Python programming language: post-processing of experimental data, image analysis
- curiosity or desire to enter the world of research

Work Context

The Institut Clément Ader (ICA, CNRS UMR 5312) is a research laboratory dedicated to the study of mechanical structures, systems and processes. Our sectors of activity fall within those of the mechanical industries, with particular attention paid to projects in the fields of aeronautics, space, transport and energy. Our work generally focuses on modelling the mechanical behaviour of materials, its instrumentation and the study of the durability of the structures or products considered.

The ICA has about 80 research professors, 20 temporary researchers, 20 administrative staff, 90 doctoral students, as well as many interns. With the particularity of having :
- at the level of the supervisory bodies, staff belonging to four major institutions: UPS and INSA from the Ministry of Higher Education and Research, ISAE from the Ministry of Defence, Mines Albi from the Ministry of Industry;
- geographically, the staff is spread over four cities in the Midi-Pyrénées/Occitanie region: Albi, Figeac, Tarbes and Toulouse.
The management is composed of a director and two deputy directors, the three supervisory ministries being represented in this trio. The technical support team (BIATSS staff) is organised into three components, one for each ministry.

The laboratory is organised into four research groups:
- MSC group: Composite Materials and Structures ;
- SUMO Group: Surface, Machining, Materials and Tools;
- MS2M Group: Modelling of Mechanical Systems and Microsystems;
- MICS Group: Metrology, Identification, Control and Monitoring.

This research work is in line with the research themes of the MICS, SUMO and MS2M groups, for the understanding and metrological development associated with surface reactivity phenomena assisted by mechanical deformation.

The skills required of the engineer are centered on the understanding of the physical and chemical mechanisms responsible for the thermomechanical behavior of materials, particularly at small scales and subject to complex environments (oxidizing environment, extreme thermal environments, etc.). The studies around the micromechanical theme require the definition, design and development of characterization techniques towards small scales. Moreover, the research engineer will participate to the activities on the measurement of kinematic fields at small scales at high temperatures and the digital implementation of crystalline plasticity on real aggregates. The main mission of the research engineer will be to accompany this evolution of the ICA's research activities by contributing to the production of experimental results related to the characterization of the thermo-mechanical behavior at small scales in oxidizing environments on titanium alloys.
Location :
Institut Clément Ader (ICA) – UMR CNRS 5312
3, rue Caroline Aigle
31400 Toulouse, France

The position is located in a sector under the protection of scientific and technical potential (PPST), and therefore requires, in accordance with the regulations, that your arrival is authorized by the competent authority of the MESR.

Constraints and risks

Nothing to add

Additional Information

This work is part of the ERC Starting Grant - HT-S4DefOx: High temperature - small scale sub-surface deformation assisted by oxidation.

Minimum 5 years of higher education, with an engineering degree or equivalent professional experience, specializing in mechanics and materials.