Springback in stringer sheet stretch forming

Stringer sheets are sheet metal structures stiffened by bifurcations in the cross-section. In order to create spatially curved light-weight structures they may serve as preforms for sheet metal hydroforming. The stiffness of sheets altered by stringers is expected to affect the hydroforming results. In particular influences of the geometric inhomogeneity on the extent and orientation of springback are of interest. They are investigated by means of mathematical analysis and forming experiments. A modal analysis of formed stringer sheets is conducted in order to understand the different impacts of stringers on the elastic behaviour of parts and springback after forming.