【作者】 武延民；

【导师】 江见鲸； 王元清；

【作者基本信息】 清华大学 ， 土木工程， 2005， 博士

【摘要】 随着钢结构在我国的广泛应用,其工作环境也日益复杂,越来越多的钢结构应用于低温环境,尤其是高原严寒地区,同时高强度钢材和厚板开始在部分工程中得到应用,低温环境、高强度钢材和厚板的使用以及钢结构中常用的焊接连接使得钢结构脆性断裂的问题日趋突出。目前国内的钢结构设计规范中对钢结构低温脆断的控制还很不完善,不能够对构件是否发生脆性断裂进行定量的准确判断和分析。本文对结构钢材低温力学性能和断裂韧度性能进行了试验研究和计算分析,分析应力状态对构件脆性破坏的影响,进而提出了钢结构低温冷脆的实用设计方法。论文主要取得了如下成果: (1)对常用结构钢材(Q235、Q345 和Q390)和桥梁钢材(16Mnq、14MnNbq)低温下的力学性质进行了试验研究,获得了在20℃~-70℃范围内钢材的强度指标和塑性指标,并研究了其随温度的变化规律。(2)对结构钢材(Q235、Q345 和Q390)的断裂韧度指标进行了低温试验研究,重点测定了20℃~-70℃范围内12mm~48mm 厚度试样的断裂韧度CTOD指标,分析了其变化规律。本文根据试验结果对断裂判据指标进行了选取;同时通过理论模型和非线性有限元方法分析了温度对裂纹尖端张开位移的影响,提出了不同温度下裂纹尖端张开位移的计算公式。(3)采用有限元的方法分析了缺口和裂纹尖端的应力场分布规律;从理论角度分析了应力状态对构件破坏行为的影响。(4)提出了钢结构断裂模式的分析方法和钢结构低温脆断设计方法。首先根据试验结果对结构钢材的裂纹扩展阻力曲线进行分析,并对钢构件断裂行为进行了分析,提出了钢结构断裂模式的判断方法;本文提出的钢结构低温脆断设计方法分为三个级别,第0 级和第1 级适用于设计中和常规检查合格的构件,第2 级针对含有宏观裂纹的实际构件,设计方法以断裂力学为基础,可以对钢结构的低温脆断进行定量的计算分析。更多还原

【Abstract】 The working environment of structural steels becomes more complicated as it is widely used. More steel structures are working at low temperature, especially in altiplano and cold zone. High strength steel and thick plate begin to applied in some structures. Low temperature, high strength steel, usage of thick plate and jointing connection usually used in steel structures make the problem of brittle fracture of steel structures more important. Nowdays, the control of brittle fracture of steel structures in code for design of steel structures in China is incomplete, which could not give exact judgement and quantitative analysis on the brittle fracture. This paper researches the mechanical properties and fracture properties with experiments at low temperature, and analyzes the influences of stress status on fracture mode, and finally proposes the applicable brittle fracture prevention design method. The main conclusions of this paper are as following: (1)This paper measures the mechanical properties of structural steels(Q235、Q345 and Q390) and bridge steels(16Mnq and 14MnNbq) with experiments at low temperature, acquires the strength parameters and plastic parameters at temperature 20℃to -70℃. The variation of the properties with temperature is also studied. (2)This paper researches the fracture properties of structural steels(Q235、Q345 and Q390) with experiments at low temperature, measures the fracture toughness CTOD for plate with 12mm to 48mm thickness at temperature 20℃to -70℃, and studies the variation of CTOD with temperature. This paper analyzes the fracture criteria for prevention design based on the experiments and also analyzes the influences of temperature on CTOD, and proposes the equation for CTOD at different temperatur. (3)This paper analyzes the three dimensional stress at crack tip with the FEA method, and analyzes the influences of stress status on fracture behavior in theory. (4)This paper proposes the analytical method for fracture mode and design method for prevention of brittle fracture at low temperature. This paper firstly studies the R-curves of structural steels from the experimental results, then analyzes the fracture behavior of steel structures based on experimental results, and finally proposes analytical method for judgement of fracture mode. The design method for prevention of brittle fracture at low temperature is devided into three degrees. The zero degree and 1th degree is used in the design and for the steel structures satisfying regular inspection. The 2nd degress is for the structure with macro-cracks. The design method is based on fracture mechanics and provides quantitative judgement and analysis for the brittle fracture of steel structures.更多还原