基于复合型裂纹扩展机理的钢结构精细化疲劳评估方法研究

In terms of the situation that the universality and accuracy of the existing fatigue assessment approaches is not sufficient, this project is planned to systematically investigate refined fatigue assessment approach which can precisely consider the mix-mode crack propagation mechanism, based on the urgent needs of the rapid development of steel structure constructions in China. Firstly, the three dimensional mix-mode fatigue crack propagation simulation approach will be established, on the basis of the determination of mix-mode crack kink angle, the calculation approach of the equivalent stress intensity factor and the application of the adaptive meshing technique. The reliability of the proposed approach will be carefully verified by fatigue tests on several groups of steel plates containing the middle inclined through crack. Secondly, multi-crack propagation analysis will be implemented based on the further optimization of the adaptive meshing technique. The reliability of the simulation will be verified by fatigue tests on several steel girders. Lastly, the proposed mix-mode fatigue crack propagation simulation approach will be applied in multi-scale finite element models using the developed program coded by Python and its effectiveness will be verified furthermore. With the reliable approach in multi-scale models, the quantitative evaluation method will be proposed in terms of the influence on fatigue assessment caused by the global-local coupling effect. The achievements of this project will be of important theoretical and realistic significance for the improvement of fatigue assessment theory, promoting the application of new steel materials, new structural details, new manufacturing techniques, ensuring the safety of the exist steel structures and serving for the rapid and healthy development of the steel structure constructions in China.

本项目拟针对现有疲劳评估方法普适性和精确性较低的现状，紧密结合我国钢结构建设快速发展的迫切需求，系统开展基于复合型裂纹扩展机理的钢结构精细化疲劳评估方法研究。通过确定复合型疲劳裂纹扩展方向判定准则、等效应力强度因子计算方法及引入自适应网格划分技术，实现三维复合型疲劳裂纹扩展模拟方法，并通过开展多组中心斜裂纹钢板疲劳试验验证方法的可靠性；通过对自适应网格划分技术的进一步优化，实现多个复合型裂纹扩展模拟，并通过钢梁疲劳试验对数值模拟方法进行充分验证；通过基于Python语言的二次开发，在多尺度模型中实现并验证复合型疲劳裂纹扩展模拟方法，建立整体-局部耦合关联对疲劳寿命影响的定量评价方法，将断裂力学评估方法推广至构件和结构层面。研究成果对于完善疲劳评估领域的科学理论、促进新钢材、新构造、新工艺的推广应用、保障既有钢结构运维安全、服务于我国钢结构建设健康发展，具有重要的理论意义和工程价值。

现有规范多采用基于S-N曲线的名义应力法进行疲劳评估，这种方法依赖于构造细节的疲劳类别和明确的荷载历史，普适性和精确性较低。本项目基于断裂力学理论，系统开展了基于复合型裂纹扩展机理的钢结构精细化疲劳评估方法研究。以最大环向拉应力强度因子理论为裂纹扩展方向识别判据，建立了三维复合型疲劳裂纹场的扩展模拟方法。基于三种典型焊接构造疲劳试验，验证了单条三维复合型疲劳裂纹扩展模拟的准确性，提出了不同焊接构造在进行疲劳裂纹扩展分析时的初始裂纹设置建议；基于已有的正交异性桥面板疲劳试验，从裂纹扩展路径和扩展寿命两个方面均验证了多条三维复合型疲劳扩展模拟的准确性。将该方法引入多尺度数值模型中开展疲劳裂纹扩展分析，并利用已有试验数据进行充分验证，探索整体-局部耦合关联对疲劳寿命的影响规律。对比局部模型和多尺度模型得到的裂纹扩展路径和扩展寿命，表明在有限局部损伤条件下，两种模型反应出的细节疲劳性能是一致的。探索性地将临界距离理论引入钢结构疲劳裂纹萌生寿命的预测之中，提出了疲劳参数选取和具体计算方法选用的建议，并利用3个正交异性桥面板系横隔板构造细节疲劳试验数据进行验证。本项目研究成果提高了基于断裂力学的疲劳评估方法的准确度，扩大了基于断裂力学工具的疲劳评估方法的应用范围，推动基于断裂力学的疲劳评估方法应用于宏观结构层面，将促进断裂力学方法在实际工程中的推广应用，可有效降低目前疲劳评估对于大型疲劳试验的依赖程度，从而大幅降低疲劳评估所需的经济代价，可为新钢材、新构造、新工艺的推广应用和既有钢结构的科学运维提供有益的技术支撑，具有积极的科学意义和广泛的应用前景。