Investigation of creep-age forming of aluminum lithium alloy stiffened panel with complex structures and variable curvature

Creep-age forming (CAF) is one of the effective techniques to fabricate extra-large integral airframe panels due to its good forming ability. However, few experimental researches have been conducted on stiffened panel with complex structures under creep-aging condition. In this work, a 1096 × 792-mm stiffened panel with typical structure features, such as stiffeners, the base plate with variable thickness, and the opening, has been formed on the tool of variable curvature at 165 °C for 10 h. Springback of the stiffened panel in static loading process is 91.1%, while it decreases to 82.3% after 10-h creep aging, which shows that plastic and creep deformation play an equivalent role in restraining the springback of the panel. Deformation of the stiffened panel concentrates around the opening with thicker plate and larger curvature, while little deformation occurs in the base plate with varied thickness or stiffeners. It indicates that the size, orientation, and position of the structure features all have significant impact on final shape of the stiffened panel. The accuracy of the corresponding finite element (FE) simulation has been verified by the fact that the proportion of the area, where the gap between the simulated and the experimental part is less than 0.6 mm, accounts for more than 90%.