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Short description

In civil and mechanical engineering, damage caused by load cycles with large plastic amplitudes are frequently reported. A typical failure mechanism is the fracture due to ultra-low-cycle-fatigue in case of seismic events. As reported from the devastating earthquakes in Northridge and Kobe such failures were often the result of insufficient deformation capacity in combination with non-appropriate toughness properties of the steel material.
Eurocode 3 provides a procedure for the choice of steel material in the lower part of the toughness-temperature-diagram to avoid brittle fracture. Concerning plastic design, there are some empirical rules in EC3 and 8 for monotonic and cyclic loading, but these rules are related to ductility and are not justified by toughness considerations. All these recommendations are rather general and need a mechanical justification or a substitution by substantiated realistic material requirement. As a consequence EC3 and 8 need extension in terms of toughness-related demands for plastic design. First promising attempts by means of innovative damage mechanics on how to ensure a sufficient ductile behaviour related to toughness demands have been developed in the RFCS-Project PLASTOTOUGH. The original nature of damage mechanics is physically based and related to the micromechanical processes in the metallic structure. This method has been successfully applied to welded beam-column-connections in combination with the effective plastic strain concept acc. to Ohata and Toyada. However, recent research has shown that the damage model needs extension in case of dominant shear stress by considering the third invariant of the stress deviator. To verify this new approach its application to components with a high portion of shear stress is to be investigated. As damage mechanics based quantities do not constitute appropriate material properties the definition of a minimum Charpy impact value as toughness parameter in the
upper shelf would be suitable.

Research program

RFCS - Research Fund for Coal and Steel



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