Laser shock peening on fatigue crack growth behaviour of aluminium alloy

Abstract

A B S T R A C TThe effect of laser shock peening (LPS) in the fatigue crack growth behaviour of a 2024-T3 aluminium alloy with various notch geometries was investigated. LPS was performed under a 'confined ablation mode' using an Nd: glass laser at a laser power density of 5 GW cm −2 . A black paint coating layer and water layer was used as a sacrificial and plasma confinement layer, respectively. The shock wave propagates into the material, causing the surface layer to deform plastically, and thereby, develop a residual compressive stress at the surface. The residual compressive stress as a function of depth was measured by X-ray diffraction technique. The fatigue crack initiation life and fatigue crack growth rates of an Al alloy with different preexisting notch configurations were characterized and compared with those of the unpeened material. The results clearly show that LSP is an effective surface treatment technique for suppressing the fatigue crack growth of Al alloys with various preexisting notch configurations.Keywords fatigue behaviour; laser shock peening; residual stress. I N T R O D U C T I O NLaser shock peening (LSP) is a premising surface treatment technique and has been shown to be effective in improving the fatigue properties of a number of metals and alloys. The process was originally developed at the Battelle Columbus Laboratory in 1970s. 1-6 Since then, considerable attention has been paid to potential applications of LSP in the aerospace and automotive industries.The beneficial effects of LSP on static, cyclic, fretting fatigue and stress corrosion performance of aeronautical and automotive Al alloys, steel and Ni-based alloys have been demonstrated. 7-14 LSP has also been successfully used for improving the resistance to foreign object damage of aircraft gas turbine engine blades. Laser beams can be easily directed to fatigue-critical areas, such as notches and holes, without masking. Because of its unique capability of generating large affected depths with good surface quality, LSP technology is expected to be widely applicable for improving the fatigue properties of metals and alloys, particularly those that show a positive response to shot peening. The mechanical effects of a laser-induced shock wave have Correspondence: J.-M. Yang.been evaluated to predict the plastic strain and residual stress fields induced by the impact pressure and the pressure pulse duration. A simple elastic-plastic model was developed based on the calculation of the elastic-perfectly plastic response of a material to longitudinal and planner shock wave systems. The calculated plastically affected depth, the surface plastic strain and the surface residual stress induced by LSP of an elastic-perfectly plastic material are summarized in Ref. [15]. The objectives of this work are to examine the effect of LPS on the fatigue behaviour of Al alloy specimens having fastening hole, crack stop-holes and single-edge notch. It is well known that cracks will initiate at the fastener holes in aircraft and automotive structur...

Laser Surface Treatments of Aluminum Alloys

“…In their report, the residual stress profiles of the treated samples after multiple LSP impacts with the impact time as functions of the distance from the top surface are shown in Figure 41. The substrates are approximately in the zero-stress state, indicating that the effect of initial stress on the shock waves may be ignored (Tan et al, 2004). It can be noted from Figure 41 that the significant compressive residual stresses mainly exist in near-surface regions for all cases and the top surfaces have the maximum values of compressive residual stresses (Lu et al, 2010).…”

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.…”

Laser Plasma Interaction and Shock Material Processing

“…Additionally, and in a parallel way, the technique has been successfully studied from a practical point of view and applied to a number of relevant material-geometry configurations involving structural materials in the aerospace, automotive, nuclear, and biomedical sectors (58)(59)(60)(61)(62)(63)(64)(65)(66)(67)(68)(69)(70)(71)(72)(73)(74)(75), its beneficial effects on static, fatigue and corrosion properties having been widely demonstrated .…”