AbstractThe introduction of Residual Stresses (RS) inside structural aerospace components has been widely studied and several techniques are now used in order to retard the crack initiation and propagation process. Among these techniques, Laser Shock Peening (LSP) has been recently applied due to its higher performance in terms of the magnitude and depth of RS introduced. Since only at the end of 1990s was a laser with high repetition rate available, LSP is a very new technique that is being gradually introduced as a method that allows introducing deep RS in both aerospace and nuclear power plant applications. Nevertheless, research around LSP is still intensive due to the large number of metal alloys where this technique can be applied, on a wide range of thickness and geometries. In parallel to the studies carried out to understand the physical phenomenon of LSP and its applications in structural engineering, analyses through the Finite Element Method have been promoted and are widely used in order to predict quickly the RS field and the associated plasticity.
This research was primarily focused on two main areas of LSP research: the understanding of the distribution of the RS in aluminium alloys after LSP treatment; and the possibility to predict them in thick samples through the Eigenstrain approach. The techniques used to measure the RS were incremental hole-drilling, neutron diffraction, and X-ray diffraction.
The investigations carried out on thick samples have shown that, under particular conditions, the Eigenstrain method is able to predict the distribution of the RS in flat areas, blended curves and round edges. Similarly, promising results were obtained where the Eigenstrains were used in order to predict the RS field in a Single Edge Notch sample that was previously Laser Peened and then Shot Peened. In parallel, a research has been carried out for thin samples subjected to LSP processing. The research involved many thin samples laser peened with different laser settings in order to better understand which laser parameters are affecting the distribution of the RS. This research included both single-face laser peening and a doubleopposite- face treatment, and it has been shown that with the use of the proper laser setting it is possible to introduce a fully-compressive RS field through the thickness.
|Date of Award||2014|
|Supervisor||Michael Fitzpatrick (Supervisor)|
- Residual stresses
- Laser peening