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Knowledge of high strain-rate deformation behavior of automotive body structural materials is of importance for design of new vehicles with improved crash-energy management characteristics. Since a large range of plastic strains is encountered during the forming process prior to assembly, the mechanical behavior of sheet steels under high strain rate deformation conditions must be understood after pre-straining, in addition to the as-produced condition. This paper presents the compression testing methodology employed to examine these properties, and focuses on the effects of quasi-static pre-strains (from 0 to 20%) on the subsequent behavior of a low carbon interstitial free steel tested over a broad range of strain rates (from 10−2 to 103s−1). The results suggest that the increase in yield stress associated with increasing strain rate is not substantially influenced by prior cold work.

Bake-hardening steels used for exposed auto-body panels provide low yield strengths before forming, and increased strength and dent resistance after the forming and paint-baking processes. Room temperature aging can alter the sheet properties before forming, after forming, or after baking. Knowledge of the evolution of mechanical properties is important, and the effects of room temperature and simulated room temperature aging (at 50°C and 100°C) on the yielding behavior and the bake hardening response of two different bake-hardening steel grades were studied. The steels included a low strength ultra-low carbon steel and a dual-phase steel with higher strength and greater bake-hardening index. Neither steel exhibited a substantial response to aging prior to tensile pre-straining, although both steels exhibited strength increases after either aging or baking following straining.