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Purpose -Laser shock peening (LSP) is a process capable of introducing compressive residual stresses into a metallic component. The residual compressive stress field can extend deeper below the treated surface than that produced by conventional shot peening (SP). The effect of such deep compressive stress profile is expected to result in a significantly greater benefit in fatigue resistance after LSP compared to SP. The purpose of this paper is to examine this further. Design/methodology/approach -Residual stress profiles have been determined by X-ray diffraction and incremental centre hole drilling. They have been correlated with the respective LSP process parameters and the obtained fatigue behavior. Findings -A significant improvement of the fatigue life was found for an R ratio of 0.1. SP leads to a fatigue improvement of about 15 percent. For the same specimen geometry, a fatigue life improvement of about 25-35 percent, depending on the load level, can be obtained after LSP. However, not only for the positive R ratio, where it is quite obvious, but also for the negative R ratios, R ¼ 2 1 and 23, an increase of the fatigue life is generated by SP and LSP. Originality/value -A shown LSP has a high potential for extending the service life of metallic components at the design stage, but it may also be possible to apply this technique to in-service aircraft to extend the service goals of existing structures.

Highly loaded aircraft components have to fulfill strict fatigue and damage tolerance requirements. For some components besides the crack initiation mainly the fatigue crack propagation behavior is the main design criteria. To improve the crack propagation behavior of a component several methods are known or have been described in literature. For thin aircraft panels i.e. the application of crenellations [1] or bonded doublers [2, 3] can be a solution. For thick structures mainly the introduction of compressive residual stresses is beneficial. In this paper the potential of compressive residual stresses obtained by Laser Shock Peening (LSP) and Shot Peening (SP) is investigated. By means of Laser Shock Peening the residual compressive stress field can extend much deeper below the treated surface than that produced by conventional Shot Peening (i.e. with steel or ceramic balls) [4, 5]. The effect of such deep compressive stress profile results in a significantly higher benefit in fatigue behavior after Laser Shock Peening or after the combination of Laser Shock Peening and Shot Peening on top. The measurement of residual stresses as a depth profile has been performed by incremental hole drilling (ICHD) and contour method. Finally crack propagation tests have been carried out to validate the process technology approach.

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