Durability Evaluation of Formed Mild and High Strength Sheet Steel Structures

High strength sheet steels provide great potentials for modern light weight automotive body structures. With innovative forming technologies such as hydroforming, their capabilities can be increased due to the material properties. The investigated mild and high strength steels show a significantly increased yield strength due to uni- or biaxial prestraining. Under cyclic loading with plastification the prestrained materials soften, depending on the forming grade and the strain amplitude. The increase of the yield strength however can be preserved under strain amplitudes in the elastic range. The proposed numerical method for durability evaluation is based on finite element stress analysis and cyclic material properties determined on prestrained material specimens. The method is demonstrated and verified on an idealized component with defined forming grades in highly loaded areas. Of special interest is the high fatigue strength of structures made from high strength steels.