Prediction of plastic instability and forming limits in sheet metal forming

Şanay, Berkay
The Forming Limit Diagram (FLD) is a widely used concept to represent the formability of thin metallic sheets. In sheet metal forming processes, plastic instability may occur, leading to defective products. In order to manufacture defect free products, the prediction of the forming limits of sheet metals is a very important issue. FLD’s can be obtained by several experimental, empirical and theoretical methods. However, the suitability and the accuracy of these methods for a given material may vary. In this study, FLD’s are predicted by simulating Nakazima test using finite element software Pam-Stamp 2G. Strain propagation phenomenon is used to evaluate the limit strains from the finite element simulations. Two different anisotropic materials, AA2024-O and SAE 1006, are considered throughout the study and for each material, 7 different specimen geometries are analyzed. Furthermore, FLD’s are predicted by theoretical approaches namely; Keeler’s model, maximum load criteria, Swift-Hill model and Storen-Rice model. At the end of the study, the obtained FLD’s are compared with the experimental results. It has been found that strain propagation phenomenon results for SAE 1006 are in a good agreement with the experimental results; however it is not for AA2024-O. In addition, theoretical models show some variations depending on the material considered. It has been observed that forming limit prediction using strain propagation phenomena with FE method can substantially reduce the time and cost for experimental work and trial and error process.


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Citation Formats
B. Şanay, “Prediction of plastic instability and forming limits in sheet metal forming,” M.S. - Master of Science, Middle East Technical University, 2010.