Computational Simulation of Ductile Fracture in Structural Steel System

本研究计划将建立一个计算模拟框架，以捕捉延性断裂对建筑物中结构钢构件的影响。 钢结构在美国的建筑和桥梁库存中占很大一部分。当构件超过弹性极限并承受循环荷载时，就会发生延性断裂。由于地震、海啸和飓风引起的极端载荷会导致与韧性断裂相关的结构失效。 确定钢结构的结构安全性关键取决于预测延性断裂影响的能力。目前，评估韧性断裂起始和扩展的主要手段是通过全尺寸实验。 然而，它是经济和物理上禁止进行各种情况下的大规模实验。 现有的分析表达式来预测韧性断裂起始不产生有关随后的断裂扩展的信息，并且需要预先识别断裂将在结构中发生的确切位置。 这项研究将采用计算模拟来填补关于如何预测韧性断裂的产生和传播的知识的关键空白，从而提高建筑环境的安全性和性能。综合教育和推广活动将有利于本科生和研究生，并将激发K-12学生对工程的兴趣。该项目将通过实施新版本的扩展有限元方法来捕获低周疲劳和延性断裂对结构钢部件和系统的影响。 断裂准则将取决于与非弹性功和损伤累积有关的量。将使用新的薄钢元件实验测试方法校准分析方法，以更好地产生屈曲位置处发生的应力和应变状态。将对这些新的测试技术进行研究和改进，以克服将标准低周疲劳测试方法应用于薄钢元件的挑战，同时还捕获表面条件，冷加工和材料变化的影响。此外，将进行结构部件测试，以验证计算模拟框架。新的分析方法将允许在计算模拟中描述损伤累积、断裂起始和断裂扩展，同时消除对极细网格的要求，以捕获由裂纹引入的尖锐应力和应变梯度。

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.