Numerical modeling of integrally stiffened structures forming from creep age forming technique

Creep age-forming process has been developed and used to manufacture complex-shaped panel components in aerospace applications to improve performance and to significantly reduce fabrication costs. In this study, this technique is applied to the manufacturing of integrally stiffened structures. To form such structures, two main problems are encountered, the first one concerns the formability limit (limit curvature radius) of the stiffeners in order to avoid plastic instabilities, the second one is the springback of the stiffened sheet. To better evaluate the technique, a finite element modelling taking into account the thermo-elasto-viscoplatic behavior of the considered aluminium alloy and stress relaxation phenomena which takes place during the thermal exposure (creep-ageing stage) is proposed. Numerical finite element investigations are led in order to evaluate the influence of different mechanical boundary conditions on the final shape of a single-curved integrally stiffened structure. Results show that springback can be minimized by an appropriated choice of clamp conditions and that the final structure has both low residual stresses and plastic strains at the end of the forming stage.