TABLE OF CONTENTS Many materials display pronounced improvements in fatigue life with LSP. The beneficial effects of LSP may originate from surface compressive stresses in the large affected depth and improved surface quality, which delay the development of fatigue cracking. Investigations of several different aspects of the fatigue behaviours, such as fatigue life, fatigue strength and fretting fatigue, have been reported.
Investigations of aluminium alloys, steels and titanium alloys have shown that LSP can increase the fatigue strength of these materials. The initial research work focused on the effect of LSP on the fatigue crack growth of pre-existing cracks, using different laser spot shapes on the pre-cracks (Clauer et al., 1983). The two different laser spot configurations were applied around a hole in a 2024 T3 aluminium alloy specimen, shown in Fig. 2.15(a). The specimen had a cantered hole with small starter notches machined into its sides. The region around the hole was shocked simultaneously on both sides using split laser beams. One laser spot configuration used a solid spot to treat the entire region around the hole, while the other laser spot used only an annular-shaped area around the hole and notched region. The fatigue life increases for both laser spot configurations, shown in Fig. 2.15(b), and the laser-peened 2024 T3 specimens with the solid laser spot had a fatigue life about 40 times longer than the non-shocked ones, whereas those with the annular laser spot had a life about three times longer than...
