Micromechanical Simulation of Earthquake-Induced Fractures in Welded Steel Structures

[9988902] deierlein . 1994年北岭地震和1995年神户地震中观测到的地震诱发裂缝具有高应变低循环条件的特点，与桥梁中广泛研究的低应变高循环疲劳裂缝有很大不同。分析和预测高应变（非弹性）断裂的技术并不像分析其他极限状态那样发达。因此，工程研究人员目前几乎完全依靠全尺寸试验的经验数据来开发抗断裂焊接连接细节。提出的研究是开发和应用计算方法来模拟非弹性地震引起的裂缝，重点是韧性裂缝的起裂和扩展。范围包括补充计算（有限元）和实验研究，将利用最先进的微观力学模型来分析延性开裂及其引发脆性解理断裂的可能性。详细的有限元分析将包括模型，考虑塑性应变和应力三轴性的相互作用，导致空洞的增长和合并。微观力学模型的结果将与常规断裂指数（KI， J， CTOD）进行比较，物理测试将用于校准母材和焊缝金属的应力/应变和断裂韧性性能，并验证模拟结果。与新日铁株式会社和千叶大学的研究人员合作，将提供机会研究神户地震后进行的大量日本研究的数据。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."