The influence of spot overlap and laser flence on the high cycle fatigue (HCF) strength of aircraft engine fan blades

Analysis of laser shock waves and resulting surface deformations in an Al–Cu–Li aluminum alloy

“…A 50 µm x-ray collimator was used at ICB-Dijon for analysing stress distributions, corresponding, after beam divergence, to a 100 µm XRD spot on the metal. Despite the apparently large grain sizes, the use of a classical sin 2 approach was shown to be possible with a 100 µm XRD spot, due to the presence of partially recrystallized areas in Al grains (figure 3(a)), which acted as sub-diffracting domains. Another important point is that the EBSD and XRD techniques did not probe the same depth (less than 0.1 µm for EBSD and 6-9 µm for XRD).…”

“…Over the last 30 years, laser shock processing (LSP) has been proposed as a competitive alternative technology to classical surface treatments for improving fatigue, corrosion and wear resistance of metals. It has recently been developed as a practical process amenable to production engineering in aeronautical engines [1], or nuclear power plants [2]. This process aims at introducing a deep (mm range) residual compressive stress field on metallic targets, through the generation of a laser-induced high-pressure plasma.…”

“…This process aims at introducing a deep (mm range) residual compressive stress field on metallic targets, through the generation of a laser-induced high-pressure plasma. More precisely, the process can be summarized as indicated in the following four-stage sequence: (1) laser pulses (in the GW cm −2 range) impact the surface of a metal immersed in water (figure 1), and ablate a thin layer of the surface (less than 1 µm/shot), (2) the vapour continues to absorb the remaining laser energy which ionizes into a high-pressure plasma, (3) due to the confining effect of water, the plasma pressure is amplified (up to several GPa), and the resulting pressure discontinuity propagates into the material as a shock wave [3,4], (4) the resulting heterogeneous plastic deformation of the metallic target imparts compressive stresses. Usually, the plasma confined regime allows maximum impact pressures of up to 5 GPa in the 8-10 GW cm −2 intensity regime for 10-20 ns pulse duration, as experimentally shown in [4].…”

FEM calculation of residual stresses induced by laser shock processing in stainless steels

“…For a single laser impact, the residual stress profile was rather well reproduced by the thermo-mechanical simulation (figure 10(b)), particularly the thermally affected zone (30 µm), where residual stresses are tensile (+900 MPa maximum value). Future developments are under investigation to consider a large number of impacts followed by unique thermal effects (which is nearly the same at each impact) and to try to investigate the unusual compressive RS fields induced without coating in nuclear power plants [5].…”

“…Among the recognized industrial applications for LSP, one can mention the treatment of fan blade sharp edges against flying object damage (FOD) [4], the reinforcement of heat affected zones close to sensitized welded joints in nuclear power plants [5] and numerous oncoming applications for which patents have been already acquired by the GE Company [6]. Recently, special funds from the US government to improve the applicability of the treatment, together with the emergence of new high cadency laser sources [6], have increased the number of studies about LSP.…”