Laser peening is an emerging technology for the surface treatment of metallic materials that is capable of enhancing resistance to failure by fatigue and corrosion. In the laser peening process, a laser pulse is directed at a metallic surface, producing a planar shockwave that travels through the material, plastically deforming material and producing a layer of near-surface compressive residual stress. In comparison with conventional peening techniques, laser peening produces significantly deeper residual stress at lower levels of cold work, and with a smoother surface finish. Each of these characteristics contributes to the ability of laser peening to provide greater service life extension for treated components than achievable with many other surface treatment processes. The process therefore holds great promise for service life extension of both new and fielded components.

This paper describes some recent results from joint research programs conducted to generate data on residual stress and fatigue performance of laser peened materials. Specifically, we present data for residual stress imparted by laser peening and fatigue life improvement of laser peened coupons relative to as-machined coupons. These data are presented for three materials often employed in aircraft structure: 7049-T73 aluminum alloy, 7050-T7451 aluminum alloy, and Ti-6Al-4V (â-annealed) titanium alloy. For each material, residual stress distributions were measured for treatment with different laser peening parameter sets. For particular laser peening parameter sets, stress versus life data were generated for as-machined and laser peened un-notched fatigue coupons, which quantify fatigue life improvement attained by laser peening over a range of applied stress. Fatigue test data for notched 7050 coupons demonstrate that fatigue life improvement is greater in notched than in un-notched geometry. Fatigue test data for laser peened, overloaded, notched coupons show that fatigue life improvements are more resistant to compressive overload than would be anticipated based on typical strain-life fatigue analysis.