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The deformation behavior of mild steels was discussed through analyzing a typical stress-strain curve obtained from standard tension tests. Material parameters were calculated from the stress-strain curve and a power-law model was developed for this typical mild steel. Based on the calculated material parameters, material property change with pre-deformation was studied and new stress-strain curves were developed for this mild steel after different pre-deformation. A rectangular tube model related to different pre-deformation magnitudes was created using LS-DYNA. The deformation behavior of this rectangular tube under four different basic loading conditions - tension, compression, bending, and torsion - was investigated through finite element analyses. The variation of internal energy and reaction force with the magnitude of pre-deformation and subsequent structural deformation was studied.

Structural finite element analyses (FEA) are usually performed in two zones - safe zone and unsafe zone related to the status of a structure after loading. Safe zone structural FEA focus on the deformation behavior prediction of a component or a structural system. While unsafe zone structural FEA do not only focus on their deformation behavior but also their failure behavior prediction. As a fatal disaster or a high cost often results from the premature rapture of critical parts, it is very important to predict the catastrophic failure possibility and process of a component or a structural system. Unsafe zone structural FEA is one of the feasible methods making such a prediction possible. In this paper, the deformation behavior and necking process of automotive steels were discussed based on their stress-strain curves obtained from standard tension tests. New material model was developed for high strength (HS) steel through simulating a standard tension test.