Collaborative Research: Micromechanics-based Framework for Modeling Fracture of Weldments in Structural Steel

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Civil infrastructure constructed from steel relies heavily on welding to connect various parts (such as beams and columns) to each other. Welded connections are often the weak points in these structures and are prone to fracture, leading to catastrophic failure or collapse under loads such as during earthquakes. Predicting and simulating such fracture are essential for safety assessment and design of these structures. However, this type of failure is challenging to simulate in computer models, because current methods cannot properly represent the changes in material properties caused by welding processes and how these changes weaken the structure. This award will support fundamental research to understand how welding changes material properties over very small dimensions in these connections, and then will create a method to use these properties within computer simulations to predict the failure of welded connections. The findings and software technology from this research will enhance the safety and resilience of buildings and other infrastructure, benefiting the nation’s society and economy. The involvement of underrepresented groups, education of students with new knowledge, and technology transfer to practitioners will result in broad impacts. This award will contribute to the National Science Foundation role in the National Earthquake Hazards Reduction Program (NEHRP). Welded steel connections often fail under extreme loads due to the complex and multiple microstructures that are formed in weldments, and the steep stress and strain gradients that interact with these microstructures. Current methods for simulating weldments cannot simulate the mechanical properties of these microstructures or their interactions with applied loads. This is especially true when these connections are subjected to large-scale yielding or Ultra Low Cycle Fatigue fracture (which occur commonly under extreme loads such as earthquakes). This research will develop fundamental understanding of weld microstructures and their mechanical properties through laboratory experiments on thermomechanically generated samples. Then, the research will upscale these findings to the structural scale through an innovative framework of multi-scale simulation. This knowledge and framework will be implemented for convenient integration within various numerical platforms (open source as well as commercial) that are popular with researchers and structural engineers. This approach (including its implementation) will be informed and validated by extensive laboratory testing and finite element simulation, and broadly disseminated to target audiences and user groups. Data generated by this research will be archived in the Natural Hazards Engineering Research Infrastructure (NHERI) Data Depot (https://www.DesignSafe-ci.org).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.