Missions

Development of X-ray tomography image processing protocols of natural rock salt samples to characterize the evolution of the loading-induced inter- and intra-granular crack network.
Application to existing image sequences of samples subjected to triaxial mechanical and hydrogen permeation tests.

Activities

Main activities :
- Development of protocols to process individual 3D images: image filtering to enhance crack contrast, crack segmentation, quantitative analysis of local crack geometries (opening, orientation), statistical analysis of the crack network.
- Development of image matching protocols for a sequence of images of the same sample to quantify evolutions of crack network and sample deformations. Existing Digital Volume Correlation tools might be used in that purpose.
- Implementation of procedures to automate these operations.
- Application to a set of available imaging data (sequence of approximately ten 3D images).
- Analysis and synthesis of results.
- Presentations at meetings and conferences. Writing of scientific papers.

Secondary activities:
- Assisting other researchers in using the developed processing protocols and tools.
- Exchanging with other project components, particularly those involved in numerical simulation of rock salt behavior.
- Participating in local and global meetings for the research project.
- Contributing to additional experiments, both in the laboratory and potentially at the synchrotron.

Skills

- PhD in the field of the mechanics of heterogeneous materials or imaging and image processing techniques.
- Experience in image processing and scientific background in the mechanical behavior of materials.
- Strong motivation for the computer processing of experimental data.
- Proficiency and practice in a programming language (ideally Python and/or C).
- Ability to interact with other researchers with different cultures.
- Capacity for synthesis, particularly with a view to presenting results and writing scientific articles.

Work Context

The candidate will join the “Multi-Scale Modeling and Experimentation for Heterogeneous Solids” (ME) team of Navier laboratory, which is a joint research unit of École des Ponts, CNRS and Université Gustave Eiffel. He/she will work within the framework of the "RockStorHy" project funded by the Agence Nationale de la Recherche and which gathers 5 partners including in particular the Laboratoire de Mécanique des Solides (Ecole polytechnique) and the Centre de Geoscience (Mines ParisTech), with whom he/she will interact closely. This project addresses scientific questions raised by the storage of green hydrogen in salt caverns.

The ME team develops experimental and numerical methodologies aimed at better understanding the properties of materials and structures based on the analysis of active physical mechanisms at a finer scale. To do so, strong use is made of optical imaging and X-ray tomography techniques, in the laboratory and on synchrotron beamlines, and in situ mechanical loading devices. The images are used qualitatively and quantitatively using general use softwares (e.g. FiJi software, Python libraries) as well as specific inhouse tools (e.g. for image correlation analysis).

The recruited candidate will be trained in the use of these resources and softwares and will benefit from the assistance of the researchers and engineers involved in the project. He/she will interact with another postdoctoral fellow from the project, who is already in the laboratory and working on other image sequences produced by two thesis projects currently nearing completion. The sharing of tasks and tools between the various stakeholders, mutually agreed upon with the project leader, should enable the efficient exploitation of the numerous 3D images acquired during the RockStorHy project and the drawing of relevant conclusions about the behavior of salt near future hydrogen storage cavities.

More specifically, the 3D image sequence that is proposed to be processed in this project results from several experiments on a natural coarse-grained rock salt that combined triaxial mechanical and hydrogen permeation tests, conducted by the Geoscience Center, and ex-situ tomographic imaging carried out by the Navier laboratory at each stage of the loading history.

Constraints and risks

Possible participation in tomography experiments, in the laboratory or on a synchrotron facility, requires compliance with the associated radiation safety rules. Subject to the application of the latter, the experiments are without risk.