基于断裂力学的钢桥疲劳裂纹扩展与寿命评估方法研究

发布时间：2018-06-29 09:59

本文选题：钢桥 + 断裂力学　；参考：《清华大学》2015年博士论文

【摘要】：目前,各国规范普遍采用基于S-N曲线的名义应力法对钢桥细节进行疲劳评估,而这种方法往往依赖于构造细节的疲劳类别和荷载历史。当面对新型连接和节点或采用新型钢材的构造时,通常需要开展疲劳试验,但试验费用昂贵且结果往往缺乏普遍适用性。针对这一现状,本文基于断裂力学理论,开展了对钢桥疲劳问题的研究,主要的研究工作和成果如下:(1)在三种应力比条件下,完成了三种厚度、共计54个Q345qD钢紧凑拉伸试样及10.0mm厚、共计18个WNQ570钢紧凑拉伸试样的疲劳裂纹扩展速率试验。分别采用成组数据法和单试件数据法,提出了Q345qD和WNQ570母材及焊缝的基于Paris公式的疲劳裂纹扩展速率参数标准值,给出了开展疲劳评估时参数的选用建议,为相关工程的疲劳评估提供了重要的基础数据。(2)选取三种典型的焊接构造细节——不等厚对接焊缝、十字形传力角焊缝和十字形非传力角焊缝,完成了共计78个试件的疲劳试验,细致测量了试件的几何外观、初始裂纹位置和应变数据,并验证了现行规范中疲劳设计曲线的适用性。(3)实现了基于FRANC3D和ABAQUS交互平台的复合型疲劳裂纹扩展分析方法。利用已完成的焊接构造疲劳试验数据,充分验证了该方法的准确性和可靠性。在此基础上评估了三种焊接构造解析解的合理性,开展了焊接构造疲劳寿命的影响因素分析,并推荐了三种典型焊接构造的初始裂纹设置方式。(4)将复合型疲劳裂纹扩展分析方法推广至多尺度有限元模型,利用既有疲劳试验结果,验证了本方法在多尺度模型中的准确性和可靠性,并将本方法应用在一座典型铁路钢桁梁桥的疲劳评估之中。通过名义应力方法完成了该桥的疲劳构造细节危险程度排序,识别出其中最危险的两种构造细节,分别建立了每种危险细节含裂纹体的多尺度模型和单纯局部模型,预测了两种危险细节的剩余疲劳寿命。据此讨论了在开展宏观结构层面的疲劳裂纹扩展分析时采用多尺度模型的必要性,并考察了列车轴重增加对钢桥疲劳寿命的显著影响。本文形成了一种基于断裂力学手段、具有普遍适用性、经过可靠验证的疲劳评估方法,并将其推广应用至工程实际,可以有效地克服钢桥传统疲劳评估方法的不足,服务于我国钢桥建设的发展。
[Abstract]:At present, the nominal stress method based on S-N curve is widely used in many countries to evaluate the fatigue of steel bridges, and this method often depends on the fatigue type and load history of the structural details. Fatigue tests are usually required for new connections and joints or for the construction of new steels, but the test costs are expensive and the results are often not universally applicable. In this paper, based on the theory of fracture mechanics, the fatigue problem of steel bridge is studied. The main research work and results are as follows: (1) under three kinds of stress ratio conditions, three kinds of thickness have been completed. A total of 54 Q345qD steel compact tensile specimens and 10.0mm thickness, a total of 18 WNQ570 steel compact tensile specimens fatigue crack growth rate test. The standard values of fatigue crack growth rate parameters based on Paris formula for Q345qD and WNQ570 base metals and welds are presented by using group data method and single specimen data method respectively. Suggestions for selecting parameters for fatigue assessment are given. It provides important basic data for fatigue assessment of related engineering. (2) three typical welding structure details, i.e. butt weld with unequal thickness, cross force transfer fillet weld and cross non-force transmission angle weld, are selected. The fatigue tests of 78 specimens were completed, and the geometric appearance, initial crack location and strain data of the specimens were carefully measured. The applicability of fatigue design curve in current code is verified. (3) the method of composite fatigue crack growth analysis based on FRANC3D and Abaqus interactive platform is implemented. The accuracy and reliability of the method are fully verified by using the completed fatigue test data of welding structures. On this basis, the rationality of the analytical solutions of the three welding structures is evaluated, and the factors affecting the fatigue life of the welding structures are analyzed. Three kinds of initial crack setting methods for typical welding structures are recommended. (4) the composite fatigue crack propagation analysis method is extended to the finite element model at most, and the existing fatigue test results are used. The accuracy and reliability of this method in the multi-scale model are verified, and the method is applied to the fatigue assessment of a typical railway steel truss bridge. By means of nominal stress method, the dangerous degree of fatigue structural details of the bridge is sorted out, the two most dangerous structural details are identified, and the multi-scale model and the simple local model of each kind of dangerous detail with cracks are established, respectively. The residual fatigue life of two dangerous details is predicted. The necessity of using multi-scale model in fatigue crack propagation analysis at macro structural level is discussed, and the remarkable influence of axle load on fatigue life of steel bridge is investigated. In this paper, a fatigue assessment method based on fracture mechanics, which has universal applicability and has been proved to be reliable and applied to engineering practice, can effectively overcome the shortcomings of traditional fatigue assessment methods of steel bridges. It serves the development of steel bridge construction in China.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：U441.4

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