Effects of peening conditions and sheet geometry on spherical to cylindrical deformation shifts

Peen forming is a method for deforming metal sheets by introducing plastic strain near the peened surface through shot impacts. The resulting shape after peen forming is affected by peening conditions (such as shot velocity, shot diameter, and nozzle trajectory) and the specimen size. This study aimed to clarify the mechanism of the spherical to cylindrical deformation shift in peen forming, through experiments and numerical simulations using the finite element method by varying the specimen geometry, nozzle trajectory, and air pressure. The deformation of sheets, 200 mm × 200 mm × 2 mm (length, width, thickness), shifted from spherical to cylindrical at an approximate curvature of 0.4 m⁻¹. These shifts occurred at smaller curvatures in wider specimens. Numerical simulation using a three-step finite element method was used to calculate the spherical to cylindrical deformation shift. The simple spherical bending model showed that the deformation shifted from spherical to cylindrical, when the strain in the center of the thickness at the edge of the sheet was compressive. This result was consistent with the experimental and numerical simulation results.