This research project will create a computational simulation framework to capture the effect of ductile fracture on structural steel components in buildings. Steel structures constitute a significant portion of the building and bridge inventory in the United States. Ductile fracture occurs when a member goes beyond elastic limit and receives cyclic loading. Extreme loading due to earthquakes, tsunamis and hurricanes can cause structural failure associated with ductile fracture. The determination of structural safety in steel structures critically hinges on the ability to predict the effect of ductile fracture. Currently, the primary means to evaluate ductile fracture initiation and propagation is through full-scale experiments. However, it is economically and physically prohibitive to conduct large-scale experiments for various cases. Existing analytical expressions to predict ductile fracture initiation do not produce information about the subsequent fracture propagation and require the prior identification of the exact locations where fracture will occur in a structure. This research will employ computational simulation to fill a critical gap in knowledge about how to predict ductile fracture initiation and propagation, thus leading to improved safety and performance of the built environment. The integrated education and outreach activities will be beneficial for undergraduate and graduate students and will stir the interest of K-12 students in engineering.
This project will capture the effect of low-cycle fatigue and ductile fracture on structural steel components and systems by implementing a new version of the Extended Finite Element Method. The fracture criterion will depend on quantities associated with inelastic work and damage accumulation. The analysis method will be calibrated using novel experimental test methods for thin steel elements that better produce the stress and strain states which occur at buckling locations. These new test techniques will be investigated and refined to overcome challenges with applying standard low-cycle fatigue test methods to thin steel elements while also capturing the effect of surface conditions, cold-working, and material variations. Furthermore, structural component tests will be conducted to allow validation of the computational simulation framework. The new analysis method will allow the description of damage accumulation, fracture initiation and fracture propagation in computational simulation, while removing the requirements for an extremely fine mesh to capture the sharp stress and strain gradients introduced by a crack.
