Application of damage theory to structures made from high-strength steels - Prediction of component strength and ductility

In Memoriam of Prof. Dr. Bernt Johansson
It is a general question as to whether the established rules for predicting ultimate resistance under global tension can also be applied to structures made from HSS, i.e. up to fy = 960 MPa. Apart from the welding issue, for the base material, this question refers to several items, e.g. the plastic flow curve, the yield stress level, the yield ratio, the upper-shelf ductility and strainability and the lower-shelf toughness. It reveals that predicting the ductile fracture of steel components can only be an approximation, and neither allows for a deeper understanding of the real ductile crack development up to ultimate load nor leads to a realistic extrapolation if high-strength steels are used. The research work presented in this paper therefore suggests an innovative extension of the FEM analysis by implementing appropriate GTN ductile damage approaches. After a short introduction to the principles of this methodology, possibilities for its use in structural steel research and design as well as further insights into the structural behaviour of steel components, especially HSS up to S960, are presented - insights that are not possible by traditional testing or simulation.