Development and optimization of fast laser shock peening (FLSP) using most advanced laser architectures

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.