Effect of laser shock peening on high cycle fatigue failure of bolt connected AA2024-T351 hole structures

Laser shock peening (LSP) is an advanced surface treatment technique for improving the fatigue properties of various metals. However, its capability in real-engineering-based complex structures is much less reported. In this study, AA2024-T351 with circular holes, which stand for aircraft wing plates connected by bolts, are treated by LSP and then imposed to high cycle fatigue tests. Surface profiles and residual stress evolution are measured on the fatigue specimens. Microhardness, wear, and microstructure analyses are carried out on different peening specimens. Although an increment of roughness caused by periodical plastic deformation is detected on the surface, the LSP introduces a hardening layer containing a large number of dislocations, a surface with higher wear resistance, as well as a compressive residual stress layer. These LSP-induced characteristics significantly enhance the fatigue lives of both types of bolt connections we examined. Finally, the underline strengthening mechanisms are discussed from macroscopic to microscopic.