Experimental and analytical investigation of the effects of laser shock peening processing strategy on fatigue crack growth in thin 2024 aluminium alloy panels

Abstract The focus of this paper is on the use of the Laser Shock Peening (LSP) process, and the strategy with which it is employed, to retard fatigue cracks in thin metallic airframe structural panels. This approach allows for the extension of component life in both design and maintenance applications. LSP was carried out without an ablative coating. Various compressive residual stress fields were created by using different laser parameter sets, through the variation of power intensity and coverage. These were quantified using X-Ray Diffraction and Incremental Hole Drilling techniques. The size and position of the peened region was considered in order to balance induced compressive residual stresses and the resulting tensile residual stresses to obtain improved fatigue life and damage tolerance. The investigation was carried out using analytical fracture mechanics code AFGROW and validated through experimentation. Applying LSP to a pre-cracked aluminium panel provided clear retardation of the crack front as it propagated through the processed region. Decreasing the offset of the LSP region from the centre of the panel and increasing the width of the LSP region improved the results. The best configuration, a 15 mm wide LSP region with a 15 mm offset from the crack tip, yielded a fatigue life of more than 6 times the baseline fatigue value.