Laser shock peening to improve the fatigue resistance of AA7050 components

Abstract

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.

Application of the eigenstrain approach to predict the residual stress distribution in laser shock peened AA7050-T7451 samples

“…2. A complete description of all the samples involved in the broader research programme can be found in [5]. Two samples with the same geometry were laser shock peened by Metal Improvement Company (MIC), Earby, UK, with the same laser parameters but different patterns: the first one was laser peened over the upper face including the blend curved area and the lateral side as shown in Fig.…”

“…Laser Shock Peening (LSP) is a relatively new surface treatment technique which has been shown to improve fatigue life in several metal alloys including titanium alloy [1], steel [2] and several aluminium alloys for aerospace applications like AA2024 [3] and AA7050 [4,5]. In LSP a pulsed high-energy laser beam is fired onto a sample surface that is covered by a transparent layer (usually water): an opaque ablative layer (such as thin aluminium tape, or paint) is also often applied.…”

Laser Peening Process and Its Impact on Materials Properties in Comparison with Shot Peening and Ultrasonic Impact Peening

“…The higher depth of compressive residual stresses from LSP [11,75,87,88,90,100,104,112,149,170,171] made it a vital technique for such fatigue life improvement as compared to the conventional shot peening process. Furthermore, other contributing factors such as surface roughness [127] has been attributed to either the increase or decrease in fatigue life depending on the LSP processing conditions, such as the number of shocks [53].…”

“…LSP investigation on the fatigue life improvement of components was the main reason at the early stage of process development, where cracks are delayed and their propagation is retarded [ 6 , 11 , 55 , 56 , 152 , 168 , 169 ]. The higher depth of compressive residual stresses from LSP [ 11 , 75 , 87 , 88 , 90 , 100 , 104 , 112 , 149 , 170 , 171 ] made it a vital technique for such fatigue life improvement as compared to the conventional shot peening process. Furthermore, other contributing factors such as surface roughness [ 127 ] has been attributed to either the increase or decrease in fatigue life depending on the LSP processing conditions, such as the number of shocks [ 53 ].…”

A nonlinear fatigue damage‐healing model for copper film by LSP

“…21 Laser shock processing is a new surface treatment technique similar to shot peening. In recent years, several attempts have been made in the literature [22][23][24][25][26] for researching the influence of LSP. Some researches 27,28 show that LSP can also improve the fatigue resistance of metal film materials.…”