【作者】 张红胜；

【导师】 苗张木；

【作者基本信息】 武汉理工大学 ， 结构工程， 2010， 硕士

【摘要】 随着我国国力的增强、桥梁建造技术的提高,我国建造的大型、特大型钢结构桥梁越来越多,其断裂韧性的控制就显得更为重要。目前我国建造钢结构桥梁所用的韧性指标仍然是冲击韧性指标,其用于大型结构偏于危险,CTOD断裂韧性标准则比较适用。用CTOD指导钢结构桥梁防断在我国已有应用,但只是个别情况。本文在前人研究的基础上,对CTOD在钢结构桥梁防断中的应用进行了研究。本文前部分首先通过分析我国钢结构桥梁的发展现状和比较用于测试钢结构桥梁韧性的试验方法,得出CTOD试验最适合用于钢结构桥梁防断控制,为钢结构桥梁防断裂控制提供了研究方向。然后对CTOD试验,包括试验过程、理论基础进行了介绍,并根据试验经验提出了在CTOD试验中可以降低试验因素对试验结果影响的方法,即在预制疲劳裂纹过程中使各个试样固有频率相等。这种方法可以使得各个试样的预制疲劳裂纹长度基本相等,从而达到各个试样的CTOD试验条件基本相同的目的。这为更真实地得到材料的CTOD断裂韧性从方法上进行了改进。论文后部分在前人研究的基础上研究了CTOD的变化规律,包括CTOD的分布规律和对影响CTOD变化的温度与厚度因素。(1)对CTOD值的分布规律进行了研究,通过对14MnNbq母材的CTOD数据进行了拟合统计,结果表明在置信度为95%的情况下,以上三种统计分布函数都接受拟合检验,经过比较,三参数威布尔分布函数的拟合效果最佳。(2)在前人对桥梁钢CTOD断裂韧性研究的基础上,经过自己的分析,得出结论：温度和厚度因素对桥梁钢CTOD值的影响需要分别考虑,并对常用桥梁钢的CTOD与温度的关系进行了研究,得到了基于数据拟合的规律。(3)在小范围屈服的条件下,提出了厚度对CTOD值影响的数学表达式,为工程应用提供参考。另外,通过对常用桥梁钢的CTOD数据进行拟合,得出了CTOD随温度和厚度变化的表达式,为工程应用提供了便利。(4)根据CTOD-温度曲线的特点,提出将曲线上下平台值和的一半定为工程上的CTOD验收值,而该值下的温度为CTOD韧脆转变温度,并分别计算出了14MnNbq焊缝、16Mnq母材和焊缝的CTOD验收值。这为钢结构桥梁的防断控制提供了依据。更多还原

【Abstract】 With the enhancement of our country and the development of domestic technique of bridge fabrication, the number of huge steel bridges that will appear is rising. So the control of their fracture toughness appears more important. Now, in our country, the toughness indicator is still Charpy impact toughness and it is not advisable to use impact toughness for huge steel bridge. There are examples of application of CTOD during fabrication of steel bridges, but the number found is only two. Based on previous research, this dissertation is mainly about study on CTOD fracture toughness of steel bridge.The first half of this dissertation introduces test methods of toughness of structural steel for bridges. Because Charpy impact toughness has the advantages of sample operation and low fee, it is applied speedily in engineering. Though series of impact tests under different temperatures, we could establish a curve of impact absorbing energy versus temperature. Then the transformation temperature of impact toughness could be obtained. Deep notched wide plate test is based on linear plastic fracture mechanics and its purpose is to get the critical plane stress intensity factor KC of materials tested, namely resisting force. The relationship of KC and impact transformation temperature, established through statistical means, is amended and then the limit thickness of structure under different temperatures could be determined. However, it is a little dangerous to use the toughness indicator of Charpy impact test for huge steel bridges. Neither, wide plate test is not effective in the situation of large-scale yielding. In order to test the most approximate toughness of real steel bridges and to take full advantage of materials, CTOD test is advisable.The second half of this dissertation talks about the scatter of CTOD values and the effect of temperature and thickness to CTOD values for bridge steel. Just as impact test, CTOD test results appear temperature-transformation phenomenon. In transformation region of CTOD-temperature curve, CTOD values have conspicuous scatter which cannot be neglected. Processing CTOD data of 14MnNbq steel by means of statistical fit, the result is that CTOD values obey the laws of normal distribution, logarithmic normal distribution and three-parameter Weibull distribution. The most effective distribution is the last one. Temperature and thickness are main factors that affect CTOD value and also are the most interested ones. The effect that temperature brings to CTOD value could be shown clearly through a S-shape curve which could be got by series of CTOD tests under different temperature. The effect of thickness to CTOD value is presented by a math formula which is deduced theoretically. At last, according to the characteristics of CTOD-temperature curve, a kind of CTOD criterion is proposed. Define the half of sum of upper platform value and lower platform value as acceptable value of bridge steel and the corresponding temperature as CTOD ductile-brittle transformation temperature. This criterion could be applied to control of fracture toughness of steel bridge.更多还原