Numerical Modelling of Toughness and Failure Processes in Steel Structures

The necessity to avoid failure of steel structures often results in conservative design as the load bearing capacity of structures cannot be quantified precisely with the common design tools mainly focussing on strength properties. Nevertheless, recent developments in mechanical and civil engineering show tendencies to an optimized utilization of the material properties. This requires improved understanding of failure behaviour and precise failure prediction tools. In this work, damage mechanics failure criteria and models are discussed which can be applied for failure prediction. For the Gurson‐Tvergaard‐Needleman (GTN) model, physical interpretations of the model parameters are presented which help for a reliable and reproducible failure prediction. Procedures for parameter quantification are demonstrated as well. In the second part, examples for successful application of damage models to industrial problems are presented. Ductile crack initiation during offshore laying of pipelines is simulated in large scale bending tests and predicted quantitatively both with the GTN model and with damage curves, and a numerical prediction of physical upper shelf crack initiation values is shown. A correlation between size distributions of voids on ductile fracture surfaces and adequate FE mesh size is suggested to overcome the mesh size sensitivity of the GTN model. Finally, the complex failure behaviour of multiphase steels with cleavage and ductile failure appearances is simulated numerically by coupling of the GTN model and the Cohesive Zone model.