Missions

Laser Shock Peening (LSP) techniques are used to introduce high levels of residual stress into a metal part in a controlled manner. In this process, a high-energy, short-duration laser pulse is focused on the surface of a sample, ablating the surface material and forming a plasma. When the plasma expands, it exerts a high-intensity pressure on the surface of the sample, resulting in residual surface stress (RS). A shock wave propagating through the core of the structure also results from this expansion. Repetition of this step enables a large surface area to be treated. In most cases, the study of CR requires the use of (semi-)destructive techniques, which are costly and/or dangerous. These constraints further complicate the study of the dynamics of RC generation. A number of methods based on acoustic wave propagation have been proposed for the a posteriori study of residual stresses in materials. However, few studies are currently focusing on the dynamics of residual stress formation using acoustic waves. Due to their near-surface location, one avenue for acoustically probing CRs lies in the use of surface acoustic waves, known as Rayleigh waves. Due to their non-linear nature, shock waves can exhibit unique behaviors in relation to elastic and acoustic waves. In particular, unique regimes are observed in fluids when a wave reflects obliquely off a free wall. If the shock wave is said to be weak, the von Neumann reflection regime can be observed: the wave appears to be reflected at a distance from the wall, the incident and reflected angles are not equal, and a third wave, called the Mach foot, appears running along the wall and connecting it to a triple point where the incident and reflected waves meet. The existence of this regime has been observed and simulated in fluids, despite the absence of an analytical description. Its presence in solids, however, remains an open question.

Activités

The post-doctoral researcher will be responsible for carrying out two studies. The two projects will be integrated into the Héphaïstos platform, located in the PIMM laboratory and dedicated to the laser generation of shock waves. - Set up an experimental set-up based on a multi-element electronic system for Rayleigh wave generation, synchronized with the laser source; - Set up an optical experimental set-up coupled to the high-energy laser source for velocimetry measurements; - Design and manufacture suitable metal samples; - Carry out measurement campaigns; - Process data; - Model using finite element simulations where possible; - Participate in various ANR LASERSHOWS projects; - Supervise trainee and assist PhD student;

Compétences

The candidate must hold a PhD in acoustics, physics or a related field. Mastery of optical assemblies is highly desirable. Knowledge of non-destructive testing techniques and the use of multi-element piezoelectric systems would be a plus. As the candidate will be required to design and manufacture samples, machining skills would be advantageous. The candidate should also have signal processing and finite element simulation skills.

Contexte de travail

The person recruited will be part of the LASERSHOW ANR project, which focuses on the study of shock wave behavior. This ANR is a collaboration between the PIMM laboratory at ENSAM and the Institut Jean le Rond d'Alembert at Sorbonne University. It will benefit from the collaboration and expertise of researchers in acoustics, materials and laser techniques.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.