Effect of prebending curvature on bending strain and surface properties of stiffened plate during prestressed ultrasonic peening

Stiffened plates are widely used in components of airplane for its light weight and high stiffness and ultrasonic peening (UP) is the key forming technology. However, insufficient bending deformation and poor mechanical properties usually appear during free UP, and elastic prestressed UP is adopted. The effect of prebending curvature radii on bending deformation and surface properties is experimentally conducted. The results show that chordwise peening path contributes to enhancement of chordwise bending strain and smaller spherical deformation. Compared with free UP, more sufficient bending deformation, larger surface hardness with smaller surface roughness, and larger and deeper compressive residual stress are generated in prestressed UP. Spherical deformation coefficient is adopted to quantitatively describe the spherical deformation. With decrease of prebending curvature radius, bending deformation, surface hardness, and absolute value of maximum compressive residual stress are significantly increased; meanwhile, the spherical deformation coefficient is obviously decreased. More uniform surface morphology and larger total depth of compressive residual stress are acquired by applying a prebending moment before UP.