【作者】 田越；

【导师】 刘晓光；

【作者基本信息】 中国铁道科学研究院 ， 桥梁与隧道工程， 2010， 博士

【摘要】 高性能钢是一种综合优化了材料力学性能,便于加工制造,可用于低温和腐蚀环境,具备较高性价比的桥梁结构用钢。它不仅保持了较高的强度,而且在材料的耐候性能、可焊性和抗脆断性能等方面都比传统的钢材有明显的提高和改善。高性能钢在相当程度上代表着钢桥用材的发展方向。本文针对国产新型500MPa级高性能钢(Q500qE)的力学性能进行了系统和全面的试验研究,力图解决高性能钢在大跨度铁路桥梁工程中推广使用所面临的技术问题。通过对500MPa级高性能桥梁钢(Q500qE)的材料和板状试样的拉伸和低应力循环、低温冲击、疲劳裂纹扩展、断裂韧性(CTOD)、铁路钢桥典型构造细节疲劳、宽板拉伸和全尺寸模型梁的静载试验和有限元分析计算等力学性能试验和研究,得到如下研究结论:①材料的屈强比与其塑性、疲劳裂纹扩展速率、低应力循环性能和断裂韧性(CTOD)关系不大,Q500qE母材虽然屈强比不同,但其延伸率都在20%以上,具有良好的塑性和较好的止裂能力以及对应力集中的再分配能力。另外,Q500qE高性能桥梁钢母材韧脆转变温度比Q370qE和Q345qD桥梁钢大大降低,具有良好的低温冲击韧性,焊缝金属韧脆转变温度与Q370qE桥梁钢焊缝相当。②随着温度的降低,44mm以下板厚Q500qE母材的断裂韧性(CTOD)变化不大,但60mm板厚Q500qE母材的断裂韧性(CTOD)在温度降至-40℃以下后,有较大幅度的降低。各种板厚的Q500qE焊缝的断裂韧性(CTOD)都比母材低。③本文提出了结合BS7910:2005对桥梁钢断裂韧性(CTOD)值进行评判,这个评定方法为运用断裂韧性(CTOD)试验评定桥梁钢及其焊接接头的断裂韧性提供了依据。④铁路钢桥5种典型构造细节的疲劳试验表明,Q500qE高性能钢与目前普遍使用的Q370qE桥梁钢对比,其典型构造细节的疲劳强度都略有提高,Q500qE高性能钢的疲劳性能能够满足铁路钢桥的要求。⑤由于强度的提高和晶粒细化,Q500qE高性能钢母材的断裂韧性Kc普遍要好于Q370qE和Q345qD桥梁钢,也高于Q500qE高性能钢焊缝。低温下Q500qE焊缝的断裂韧性Kc下降明显,但总体上,Q500qE钢板焊缝的防断性能与Q370qE钢焊缝基本相当。⑥虽然Q500qE具有较高的屈强比,但在实际构件中与Q345qD一样,可以形成塑性铰,在同样的构件截面特性下,Q500qE比Q345qD有更好的挠度变形的恢复能力。Q500qE高性能钢按照500MPa屈服强度进行设计,其强度安全储备和变形储备能够达到铁路钢桥正常的使用要求。总之,屈强比0.86以下的Q500qE高性能钢在防断、疲劳和安全性方面基本满足铁路钢桥的要求,可以应用于铁路钢桥的建设。论文有以下创新点:①首次利用材料、全厚度板材和全尺寸模型梁对高性能钢材屈强比和塑性指标进行全面的试验研究,解决了Q500qE高性能钢在铁路钢桥上应用的安全性问题。②针对断裂韧性(CTOD)值的评定问题,本文提出将CTOD试样的单边疲劳预制裂纹作为缺陷,结合BS 7910:2005《金属结构缺陷可接受性评定方法指南》的失效评定曲线FAD和标准中的2B级评定方法,对桥梁钢的CTOD值进行评定。这个评定方法为运用断裂韧性(CTOD)试验评定桥梁钢及其焊接接头的断裂韧性提供了依据。③在宽板拉伸试验中,首次研制和开发了由EVA板、自动环境温度控制系统、自动液氮灌注系统和试样表面温度传感器相结合的低温环境箱。相比现有的同类宽板拉伸试验低温环境装置,试验温度控制更加精确,自动化程度更高。更多还原

【Abstract】 High-performance steel is the higher cost-effective bridges steel with integrated optimization of the mechanical properties, easy processing, suitable for low temperature and corrosive environment. It not only maintained higher yield strength, but also increased and improved significantly in weathering resistance, weldability and resistance performance to brittle fracture than traditional bridges steel. High-performance steel represents the development trend of bridge steel in a considerable extent.The mechanical properties of a new 500MPa grade high-performance steel (Q500qE) made by China was researched systemic and tested comprehensive in this paper. It is try to solve the technical problems of high-performance steel using in large-span railway steel bridges.With the testing and research of Q500qE high-performance steel of the material and plate specimens tensile and low-cycles fatigue, low temperature impact ,fatigue crack growth, fracture toughness (CTOD), the typical construction details of railway steel bridge fatigue, wide plate tension and full-scale model beam static tests and Finite Element Analysis, etc., the main research results are as following:①Yield ratio has few relationship with the plasticity, fatigue crack growth rate, low-cycles performance and fracture toughness (CTOD). The percentage elongation of Q500qE base metal is more than 20% although the yield ratio of material is different. Q500qE has good plasticity, better ability to crack and the redistribution of stress concentration ability. Also, the brittle transition temperature of Q500qE base metal reduced greatly than the Q370qE and Q345qD bridge steel, with good low temperature impact toughness. The brittle transition temperature of Q500qE weld metal is equal to Q370qE bridge steel.②With decreasing temperature, the fracture toughness (CTOD) of 44mm thickness Q500qE base metal changed little, but the fracture toughness (CTOD) of 60mm thickness Q500qE base metal decreased obviously when temperatures down to -40℃. The fracture toughness (CTOD) of various thickness of Q500qE weld is lower than the base metal.③Combined with BS7910: 2005, the fracture toughness (CTOD) value of bridge steel and welded joints is evaluated in this paper. The evaluation method provides a basis for evaluation the fracture toughness of bridge steel and welded joints use the fracture toughness (CTOD).④The fatigue test of five typical structural details of railway steel bridge was carried out. The results indicated that Q500qE high-performance steel has slightly higher fatigue strength in the typical structural details than Q370qE bridge steel which is now used railway steel bridge widely. The fatigue properties of Q500qE high-performance steel meet the requirements of railway bridges.⑤As the strength increased and the grain refinement, the fracture toughness Kc of Q500qE high-performance steel base metal is generally better than Q370qE and Q345qD bridge steel, and is higher than Q500qE high-performance steel welded joints. At low temperatures, the fracture toughness Kc of Q500qE welded joints decreased significantly, but in general, the anti-fracture properties of Q500qE welded joints is equal to Q370qE welded joints roughly.⑥Although with high yield ratio, but in practice Q500qE can form a plastic hinge as the same component of Q345qD. And Q500qE is better than Q345qD in recovery capacity of displacement with the characteristics of components in the same section. The security test on the model beam and the material showed that: Q500qE high-performance steel meet the normal requirements of railway bridge in the strength of security reserves and deformation reserves in accordance with design by yield strength of 500MPa.In conclusion, Q500qE high-performance steel with the yield ratio of 0.86 satisfy the basic requirements of railway steel bridges in the anti-fracture, fatigue and safety, and can be used in the construction of railway steel bridges.There are innovations in this paper:①For the first time, the yield ratio and plastic of high performance steel was researched and tested comprehensive use of materials, full-size thickness plates and the full-scale model beams. It is solved of safety problems of Q500qE high-performance steel using in railway steel bridges.②For fracture toughness (CTOD) values assessment, the paper suggests that taking the single edge fatigue precrack of CTOD specimen as a flaw, combined with the failure assessment curve of FAD and the 2B-level evaluation method in BS 7910:2005 " Guide on Methods for Assessing the Acceptability of Flaws in Metallic Structures ", the CTOD value of the bridge steel can be evaluated. The evaluation method provides a basis for evaluation the fracture toughness of bridge steel and welded joints use the fracture toughness (CTOD).③In the wide plate tensile test, the low-temperature environment box is researched and development firstly which combination of the EVA board, automatic temperature control system, automatic liquid nitrogen irrigation system and temperature measure sensor of the sample surface. It is more accurate of test temperature control and higher degree of automation compared to the existing similar low-temperature environment test equipment of wide plate tensile.更多还原