Experimental research on global deformation and through-thickness residual stress in laser peen formed aluminum plates

Laser shock peening (LSP) is an emerging technique for effectively forming metal sheets due to its ability to produce higher and deeper compressive residual stress than conventional shot peening. Because it is crucial to understand the evolution of through-thickness residual stress in peening formed components, the purpose of this research was to investigate the correlation between forming deformation and altered residual stress fields in laser-peened Al7055-T7751 plates of distinct thickness. The effect of geometry thickness on global deformation and through-thickness residual stress was investigated experimentally. First, the global deformation and surface residual stress were measured and compared quantitatively. Additionally, the through-thickness of the residual stress was determined using the slitting technique, and the measurements were validated using X-ray diffraction (XRD). The experimental results indicated that the spatial distribution of the residual stress in the laser-peened plate was the superposition of the LSP-induced elastoplastic stress and the elastic bending stress. Geometry thickness not only affected bending stiffness and macroscopic deformation but also played a significant role in the evolution of residual stress across the entire section. Under the identical peening conditions, a 3-mm plate inherited a 0.5-mm compression layer with approximately 180-280 MPa stress magnitude, whereas a 9-mm plate inherited a 1-mm compression layer with approximately 340-480 MPa of stress magnitude. Further analysis revealed that the elastic bending across the section had a certain compensation effect on the compressive stress of the peened surface. Thick plates (6-9 mm) tended to inherit consistent plane stress states because they demonstrated a relatively small deformation compatibility due to the high stiffness.