Micromechanical Simulation of Earthquake-Induced Fractures in Welded Steel Structures

9988902 Deierlein以高应变低循环条件为特征，地震引起的断裂（如1994年北岭地震和1995年科比地震中观察到的断裂）与桥梁中广泛研究的低应变高循环疲劳断裂有很大不同。分析和预测高应变（非弹性）断裂的技术远不如其他极限状态的技术那么发达。 因此，工程研究人员目前几乎完全依赖于经验数据，从全面的测试，以开发抗断裂焊接连接的细节。 拟议的研究是开发和应用计算方法模拟非弹性地震引起的裂缝，重点是延性裂纹的萌生和扩展。 范围包括互补的计算（有限元）和实验研究，将利用最先进的微观力学模型来分析韧性开裂及其触发脆性解理断裂的潜力。 详细的有限元分析将包括考虑导致空隙增长和合并的塑性应变和应力三轴性的相互作用的模型。 微观力学模型的结果将与传统的断裂指数（KI，J，CTOD）进行比较，物理试验将用于校准应力/应变和断裂韧性性能的基础和焊缝金属，并验证模拟。与新日铁公司和千叶大学的研究人员合作，将提供机会研究日本在科比地震后进行的广泛研究的数据。该项目在NSF 98-36下的第三年竞争中得到支持。“美日城市地震减灾合作研究。"

9988902DeierleinCharacterized by high-strain low-cycle conditions, earthquake-induced fractures such as those observed in the 1994 Northridge and 1995 Kobe earthquakes are quite different from low-strain high-cycle fatigue fractures that have been extensively studied in bridges. Techniques to analyze and predict high-strain (inelastic) fracture are not nearly as well developed as those for other limit states. Thus, engineering researchers currently rely almost exclusively on empirical data from full-scale tests to develop fracture resistant welded connection details. The proposed research is to develop and apply computational methods for simulating inelastic earthquake-induced fractures with an emphasis on ductile crack initiation and growth. The scope includes complementary computational (finite element) and experimental studies that will utilize state-of-the-art micro-mechanical models to analyze ductile cracking and its potential for triggering brittle cleavage fracture. Detailed finite element analyses will include models that consider the interaction of plastic strains and stress triaxality that lead to void growth and coalescence. Results from the micro-mechanical models will be compared with conventional fracture indices (KI, J, CTOD), and physical tests will be used to both calibrate stress/strain and fracture toughness properties of base and weld metals and verify the simulations. Collaboration with researchers at the Nippon Steel Corporation and Chiba University will provide opportunities to study data from extensive Japanese research conducted in the aftermath of the Kobe earthquake. This project is supported under the 3rd-year competition under NSF 98-36. "US Japan Cooperative Research in Urban Earthquake Disaster Mitigation."