Springback behavior of fiber metal laminates in hat-shaped draw bending process: experimental and numerical evaluation

Abstract

Fiber metal laminates (FMLs) are one of the most applicable composite sheets that consist of metal layers and fiber-reinforced polymers. These layers are jointed to each other with epoxy or polyurethane resins. In the present study, the experimental and numerical investigations of springback in hat-shaped channel bending have been performed. At first, FMLs were produced with aluminum 2024-T3 sheets, unidirectional E-glass fibers and polyurethane resin by using a hot press with the capability of adjusting both the squeezing pressure and temperature. The specimens were produced according to the lay-up in 0° and 90° directions of metal sheets and fiber-reinforced core, then the hat-shaped channel bending was performed. Furthermore, the effect of parameters such as FML lay-up, channel depth, and core thickness on the springback angle in the flange and wall zones was studied. In the numerical section, the parameters such as plastic equivalent strain in metallic layers as well as the springback of FML with different lay-ups were investigated. The results showed that in asymmetric lay-ups where the fiber was in the longitudinal direction, the replacement of lower and upper sheets affected the springback significantly; however, where the fiber is in the transverse direction, the springback was unaffected by the same replacement. Also, due to the low elastic modulus of composite core versus metal skin, the core thickness had little effect on springback. The comparison between numerical and experimental observations showed a desirable agreement of FML geometry after unloading.