Safety assessment of steels under ULCF loading conditions with damage mechanics model

Ultra-low cycle fatigue (ULCF) loading conditions raise a complex problem for design and safe exploitation of steel constructions in seismic active zones on our planet. The investigation of the damage and failure of steel constructions under loading with large strain amplitude can contribute to the development of safety assessments for earthquake-resistant steel structures.Damage mechanics provide a good approach for the description of damage and failure of materials and structures under ULCF loading. In the frame of the presented work a coupled continuum damage mechanic material model based on Yoshida-Uemori (YU) plasticity model (Yoshida and Uemori 2003) and effective strain concept (Ohata and Toyoda 2004) is presented. In comparison with the Armstrong-Frederik and Chaboche plasticity models (Armstrong and Frederick 1966, Chaboche 1989) YU-model provides a better description for plastic material properties. Combination of YU-model model with effective strain concept and coupled damage allows using the presented model as a powerful instrument for material characterization and optimization of structures under ULCF loading.The developed damage mechanics model is validated on cyclic tests of small scale samples under loading with large strain amplitudes. It is capable to predict the force-displacement response and number of cycles to fracture. Additionally, the presented model is applicable for the simulation of large scale tests.The use of the proposed models for development of steel safety assessments and transfer of the material model parameters for modeling of large steel structures are discussed.