Multiscale model for numerical damage analyis of steel structures
The goal of the research is the analysis of steel structures considering damage evolution of the material. The remaining load-bearing capacity and the potential failure of structural members after extreme loading conditions shall be predicted.
Damage starts at the microscopic level by the initiation, growth and coalescence of voids observable as decreasing material resistance. With the formation of microcracks at the mesoscale the failure of the structural member is initiated.
The material behaviour of steel can be sufficiently modelled on a phenomenological basis within the framework of continuum damage mechanics (CDM). Viscoplasticity, hardening effects and damage evolution are taken into account for a detailed description of cyclic loading at different strain rates. The model parameters are identified with the help of an evolutionary algorithm adapting numerical to experimental results.
The nonlinear material behaviour of structures under static and dynamic loading is analysed using a displacement-based finite element formulation in 3D. To overcome mesh-dependent results in case of material softening an enhanced gradient formulation is applied which describes the distribution of locally developed damage. The nonlocal damage is introduced as an additional degree of freedom for the FEM framework. The internal length defines the size of the process zone and limits the maximum element size. Due to the small magnitude of the internal length compared to large scale 3D steel structures numerical simulations are computationally expensive.
Beam elements present a suitable approach for steel members with linear material behaviour because of the their given distinctive longitudinal dimension. While plasticity and hardening can be taken into account at the integration point softening leads again to mesh-dependent results. Damage and failure of structural members are locally restricted phenomena. Therefor, the beam ansatz functions are extended by an additional ansatz and degree of freedom to describe a kink within the element. It accounts for the plastic hinges and the loss of resistance in the course of damage evolution. The corresponding parameters for a reference beam element are identified with the help of the detailed CDM-model comparing the maximum moment and the dissipated energy.
Publications within the framework of the RTG:
Conference contribution with publication in conference proceedings:
S. Heinrich, U. Kowalsky and D. Dinkler. Multiscale damage analysis for steel structures. Proceedings in Applied Mathematics and Mechanics (PAMM), 16(1), 133-134, 2016.
U. Kowalsky, J. Meyer, S. Heinrich and D. Dinkler. A nonlocal damage model for mild steel under inelastic cyclic straining. Computational Materials Science, 2012.