In‑situ and ex‑situ study of microstructured materials subjected to a laser‑plasma‑induced shock. Application to Laser Shot Peening (M/F)

Job Description

Thesis Subject

Context

Laser shot peening (LSP) is a process that aims to introduce compressive residual stresses at the surface of a metallic material in order to improve its fatigue properties or resistance to cracking. This high‑value‑added process is already used mainly in aerospace because it can increase the durability of a mechanical part or structure, thereby reducing the frequency of replacement and the consumption of material. In practice, a high‑intensity laser (power density > GW / cm²) is applied to a millimetric‑diameter laser spot for about ten nanoseconds. Absorption at the surface creates a high‑pressure plasma (> GPa); its expansion generates a shock wave that propagates into the material. If the amplitude of this wave is sufficient, it produces a heterogeneous field of plastic strain, which ultimately generates residual stresses. Although the process has been industrially deployed for several years and many research studies have been carried out, fundamental scientific issues remain. Among them, the impact of the microstructure on shock‑wave propagation and stress‑relaxation have not been explored, even though it governs the local generation of stresses that can weaken the material, as recent numerical modelling at these scales has shown. Up to now, no experiment has been able to demonstrate this effect, because such studies require well‑controlled textured materials and temporally resolved dynamic measurements (< ns) at the grain scale (tens of microns). These are the ambitious challenges proposed for this PhD thesis.

PHD Objective

The project aims to monitor in‑situ the propagation of a laser‑induced shock and, post‑mortem, the stress fields inside specially fabricated textured materials. Measurements will be performed with time‑resolved X‑ray diffraction (picosecond resolution) or spatially resolved X-Ray diffraction (micron resolution), made possible by synchrotron and X‑FEL sources, combined with Doppler velocimetry.
The candidate will be expected to prepare, carry out and analyse experimental campaigns at the European X‑FEL in Hamburg (first campaign scheduled for December 2026), at a synchrotron source (ESRF in Grenoble or Diamond in the United Kingdom) and at the HERA laser facility in Palaiseau. Extracting stress fields under well‑defined loading conditions requires the development of inverse methods, which will be compared with new numerical models developed within the ANR L‑SPIRITS project related to the PHD. Ultimately, the aim is to optimize the LSP process by tuning its parameters (laser spot size, intensity, pulse duration and overlap rate).

Desired Skills

● The candidate must hold a master‑level degree (Bac + 5) in one of the following fields: Materials Science, Condensed‑Matter Physics, or Mechanics of Materials.
● Required skills include: curiosity and interest in multidisciplinarity, rigor and analytical skills, organizational and communication skills, ability to work in a team, and autonomy in work.
● The following would be a plus: knowledge of shock mechanics, knowledge of one or more of the following analysis techniques: X-ray diffraction, electron microscopy, proficiency in a programming language (e.g., Python), good level of written, spoken, and read English.

Your Work Environment

The candidate will join the LASER and COMET teams of the PIMM laboratory. The project is part of the Franco‑German ANR L‑SPIRITS program (principal investigator : Laurent Berthe) led by the PIMM and I2M laboratories on the French side. Possibility of teaching assignments (maximum 64 hours of teaching per year in ENSAM courses) if desired.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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