Fatigue Crack Retardation in LSP and Sp Treated Aluminium Specimens

Abstract

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.

On the application of laser shock peening for retardation of surface fatigue cracks in laser beam‐welded AA6056

“…LSP treatment has a strong beneficial effect on the fatigue performance of structural components because the compressive residual stress field induced in the material considerably retards fatigue crack growth 27–34 . Therefore, a significant improvement in the fatigue behaviour and lifetime prolongation can be achieved for components and structures with surface cracks 27,28,31,34 as well as through‐thickness cracks 29,30,32,33 . Lin et al have investigated the effect of LSP on the fatigue strength of engine components subjected to foreign object damage (FOD), where LSP is applied before FOD 35 .…”

Effects of laser shock peening on the microstructure and fatigue crack propagation behaviour of thin AA2024 specimens

“…Furthermore, a significant improvement in the FCP behaviour was demonstrated by Hombergsmeier et al (2014) [8] in the case of AA2024T3 M(T) specimens with two LSPstripes outside the initial notch. The retardation effect of LSP on the FCP rate was attributed to high compressive residual stresses, which were generated in 2 mm-thick AA2024 sheets.…”

Fatigue Life Extension of AA2024 Specimens and Integral Structures by Laser Shock Peening

“…LSP-induced residual stresses can be used to improve the damage tolerance behaviour of lightweight metallic structures. Several researches investigated the effects of LSP on the initiation and propagation of fatigue cracks in aluminium alloy specimens with various notch geometries [1,[5][6][7][8][9]. The results clearly demonstrated that LSP can be used as an effective surface treatment technique for reducing or suppressing fatigue crack growth in aluminium alloys.…”