Numerical analysis of Laser Shock Peening as a process for generation of compressive residual stresses in open hole specimens

In order to slow down the manifestation of fatigue related problems in an aircraft, or in any other metallic structure, inserting compressive residual stresses in the zone of interest is one of the approaches. Among the processes that introduce compressive residual stresses in metallic structures, Laser Shock Peening (LSP) is an emerging and a promising technique. Laser introduced plastic deformation in metallic targets has been studied since the 1960s, but it is only in the last 20 years that the technology has reached a wide industrial application not only for slowing down the fatigue related problems, but for other purposes, as well, such as forming. The compressive residual stresses induced by LSP can extend even up to several milimeters deep into the material, much deeper in respect to other conventional techniques, such as shot peening. In addition, LSP allows better accuracy and reproducibility, with smoother surface as a result, when confronted with shot peening. The downside of LSP is usually connected with longer preparation times of the specimen and equipment costs. This work gives an overview of the latest developments in the LSP technology and presents the current ongoing efforts of the University of Bologna in investigating of different aspects of the LSP process. A numerical analysis of Laser Shock Peening process is illustrated, to-gether with the effect induced by LSP in an open hole specimen geometry. This specimen is representative of a section of an aircraft fuselage lap joint, typically prone to fatigue crack nucleation at the rivet holes. The effect of the residual stress field induced by LSP on the fatigue life of open hole specimens is investigated.