M. K. Khraisheh, Masdar Institute of Science and Technology, Abu Dhabi, United Arab Emirates; M. A. Nazzal, University of Kentucky, Lexington, KY

Summary:

The current available models describing superplastic deformation do not account for a number of important characteristics describing superplastic deformation, leading to the current limited predictive capabilities of deformation and failure. These characteristics include microstructural evolution, multiaxial stress state and multiscale failure mechanisms. In this work, the effects of microstructural evolution and stress state on the deformation during superplastic forming are investigated using Finite Element simulations. The simulations are conducted using constant strain rate forming and using a new proposed optimization approach based on a multiscale failure criterion that takes into account geometrical necking, stress state, and microstructural evolution including grain growth and cavitation. The damage distribution and effective thickness distribution, which accounts for the evolution of damage, for the formed sheets are analyzed for different forming schemes. The simulations are carried out for the superplastic copper-based alloy Coronze 638, which is known to develop significant cavitation during deformation. The results clearly show the importance of accounting for microstructural evolution during superplastic forming, especially when the state of stress is biaxial. Furthermore, the results highlight the effectiveness of the proposed optimization technique in reducing forming time and maintaining the integrity of the formed part.