基于磁记忆效应的桥钢箱梁损伤量化评判理论与危险预警方法研究

Under the dynamic fatigue load, with cumulative damage and the resistance ability of steel structural bridge decreasing, the cross section of member of steel bridge will be damaged easier, which will lead to catastrophic failure of steel structural bridge. The bridge steel is a kind of the ferromagnetic material, the external load and plastic strain action causes the internal magnetic wall structure change, which changed its induction magnetic field strength by the natural geomagnetic fields, and this process has the sensitive memory effective. So it is necessary to research the magnetic nondestructive testing for steel structural bridge, and it is very important that the dangerous section or weak position of bridge can be found early than other non-destruction testing methods which couldn’t found initial damage. This project aims to diagnose the danger cross section, danger position of steel bridge structure, early warning of structural safety failure and destruction by magnetic memory effective non-destructive testing. By theoretical analysis, experimental study, numerical simulation and other means, the internal relations law and the corresponding relationship between bridge steel chemical composition, stress concentration, fatigue cumulative plastic strain, weld damage evolution and magnetic memory signal are analyzed. The bridge steel structure plastic damage-magnetic theoretical model are established, the quantitative constitutive relation between the stress concentration, plastic strain, crack propagation and other fatigue damage and magnetic memory signal are obtained. Then a quantitative evaluation method of magnetic memory testing for bridge steel structure is established, which can detect potential dangerous position and dangerous degree of bridge steel structure early, indicate the size of stress concentration and weld defects. This project has the characteristics of “magnetic” to determine the location and size of the damage, research achievement will provide a new way for nondestructive testing of steel structure bridge.

桥梁钢结构在疲劳动载作用下易产生截面损伤，随着损伤积累及抗力衰减，会引起灾变失效。桥钢属于铁磁材料，损伤演化及塑性应变改变了其磁场特性，利用磁记忆信号可以检测钢桥塑性阶段损伤，并能弥补现有无损检测不能预先诊断潜在危险的不足，研究具有重要意义。本项目旨在利用磁记忆效应无损检测钢桥危险截面、危险部位，对结构的安全失效及破坏进行预警。采用理论分析、试验研究、数值模拟等手段，研究桥钢化学成分、应力集中、疲劳累积塑性应变、焊缝损伤演化与磁记忆信号的内在联系规律及对应关系，建立桥梁钢结构塑性阶段磁-损伤理论模型，得到应力集中、塑性应变、裂纹扩展等疲劳损伤与磁记忆信号之间的量化本构关系。进而建立桥梁钢结构损伤磁记忆检测的量化评判方法，可以提早发现桥梁钢结构潜在危险部位、危险程度，指示应力集中及焊接缺陷的大小。本项目具有用“磁”来确定“损伤”发生部位与大小的特色，研究成果将为桥梁钢结构无损检测提供新方法。

桥梁钢结构在疲劳动载作用下易产生截面损伤，随着损伤积累及抗力衰减，会引起灾变失效。桥钢属于铁磁性材料，损伤演化及塑性应变改变了其磁场特性，利用磁记忆检测技术可以识别钢桥弹性及塑性阶段损伤，并能弥补现有无损检测不能预先诊断潜在危险的不足。本项目基于磁记忆检测技术，以理论分析为基础，试验数据和数值模拟为佐证，主要研究了低周疲劳载荷下结构钢磁特征参量与累积塑性损伤之间的定量关系，高周疲劳载荷下锈蚀结构钢的裂纹表征及寿命评估方法，弯曲载荷作用下钢箱梁早期隐性损伤位置与损伤程度的识别与预警方法。在理论领域，构建了基于应变的J-A磁滞回模型，合理表征了磁化强度与累积塑性应变的关系；考虑加-卸载历程对应力能的影响，修正了弹塑性力-磁本构模型，合理表征了塑性循环载荷下磁化强度与应力的关系；建立的单面V形坡口对接焊缝的应力相关三维磁荷模型以及锈蚀区的磁化相关三维磁荷模型，可准确描述焊缝和锈蚀区的磁特征。在早期诊断领域，合理的提取磁信号特征参量，比如磁信号平均值、最大值，梯度最大值等可得到试件损伤程度与磁信号的量化关系；基于磁信号特征参数特征点，可准确识别隐形损伤区并实现临界应力状态的危险预警。在数值模拟领域，实现了低周疲劳下光滑和焊接板件的力-磁耦合有限元仿真，解决了既有数值模拟参数敏感性分析不足的问题；开发了低周疲劳下光滑及焊接板件的力-磁耦合仿真应用程序，克服了传统模拟方法前（后）处理工作繁琐、数值计算效率低、参数敏感性分析不直观等问题；实现了单轴拉伸加卸载下桥梁锈蚀板件的力-磁耦合有限元仿真，与试验结果吻合较好，有限元分析所得的信号极差随拉伸荷载的增大呈现先增后减的趋势。本项目研究成果对桥梁钢结构隐性损伤、微观裂纹的早期检测以及累积疲劳损伤的定量评定提供工程实际应用依据。

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