Fatigue Crack Growth of Peened Friction Stir-Welded.pdf
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Fatigue Crack Growth of Peened Friction Stir-Welded
7075 Aluminum Alloy under Different Load Ratios
Omar Hatamleh, Scott Forth, and Anthony P. Reynolds
(Submitted April 8, 2008; in revised form March 16, 2009)
The effect of peening on the fatigue crack growth performance of friction stir-welded 7075 aluminum alloy
was investigated. The fatigue crack growth rates were assessed for laser- and shot-peening conditions at
stress ratios (R) of 0.1 and 0.7. The surface and through thickness residual stress distributions were
characterized for the different regions in the weld. The results indicate a significant reduction in fatigue
crack growth rates using laser peening compared to shot peening and the as-welded condition. The effect of
the compressive stresses obtained through laser peening was deemed responsible for increasing the resis-
tance to fatigue crack growth of the welds.
Keywords fatigue crack growth, friction stir welding, laser
peening, shot peening, stress ratio, 7075
1. Introduction
High-strength aluminum alloys, such as 7075-T7351, are
commonly used in the aerospace industry because of their
attractive properties. Unfortunately, these aluminum alloys are
difficult to weld using conventional fusion welding, and
therefore are mechanically joined at higher cost. The difficulty
in welding aluminum structure is due to the mechanical
properties of the welded joints being degraded because of the
dendritic structure formed during the fusion welding process
(Ref 1, 2).
Friction stir welding (FSW) was invented by the Welding
Institute in England (Ref 3) and is currently being targeted for
structurally demanding applications. Since its invention in
1991, FSW has emerged as a promising solid state joining
process capable of producing high-quality joints in high-
strength aluminum alloys. This technique transforms metals
into a plastic state at a temperature below the melting
temperature of the material (Ref 4, 5), and then mechanically
stirs the materials together und
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