For a proper understanding of laser shock applications, it is necessary to explore new experimental configurations and push forwards the range of configurations available. It is also important to develop theoretical and numerical models to guide these experiments, helping to reach new developments. In the present work, the latest advancements concerning laser-matter interaction will be introduced and discussed. New models were developed, associated with their experimental demonstration, concerning the expansion of a laser-induced plasma in the case of small focal spots. Furthermore, when applying a high overlapping ratio between laser shots, the material reaction to the thermal loading of the plasma was spatially resolved, helping to thwart detrimental thermal effects. Finally, a new configuration for the interaction itself, using a water tank, was also implemented and shown an increase up to 2 times of the intensity threshold for the breakdown inside the water confinement.
Laser Shock Peening (LSP) is an industrial mechanical surface treatment process used mainly by the aeronautical and nuclear industry. This process consists in focusing a high-energy pulsed laser (ns-range) on a metal target to create a high-pressure plasma that will lead to a deep plastic deformation of the target through the propagation of a shock wave. Compressive residual stresses (CRS) are generated in depth up to more than 1 mm (making this process much more effective than conventional Shot Peening), which then helps to enhance the fatigue life by slowing down crack propagation. Through theoretical and experimental studies, a new configuration has been developed: the Fast LSP (FLSP). Small laser spot sizes, high overlap ratios and high-frequencies laser for treatments is the core of this new configuration. The purpose of this work is to implement the FLSP from the laboratory to the industry. The THEIA (1 J, 10 ns, 200 Hz) laser system (made by Thales) was developed, and we investigated multiple conditions on Al-2024 samples. They were treated with various spot sizes (0.72 mm, 1.25 mm and 2 mm) and with 3 overlap ratios: 1000 %, 3000 % and 5000 %, and CRS were measured through X-Ray diffraction. A high-speed camera was used to measure both the renewing and the ejection of the water layer used to confine the plasma. Though challenges were faced, and a blowing system was developed to make sure that the ejected water will not interact with the following laser pulses, thus avoiding parasitic plasmas.
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