Inelastic effects on springback in metals

Springback from the formed state has been a subject of major concern in the design of sheet metal panels. The amount of springback is generally estimated by assuming an entirely elastic recovery process and using the established values of elastic modulus and Poissonʹs ratio. It is demonstrated that inelastic strain release from the formed state can be a major source of additional strain recovery, the magnitude of which depends on the forming stress state. Details of nonlinear recovery are studied for two different test materials, 6022-T4 Al and a high strength steel, and the results are presented here. A model based on physical mechanisms for strain recovery and compliance is proposed to describe both the tension-unloading and compression segments of deformation. Improved predictions of springback and resumption of reverse flow are possible using this model.