【作者】 宋占勋；

【导师】 谢基龙；

【作者基本信息】 北京交通大学 ， 车辆工程， 2012， 博士

【摘要】 在轨道车辆车体等工程结构上,焊接是最主要的连接方法,然而焊接结构经常发生断裂事故,其中90%为疲劳失效。影响焊接结构疲劳强度的主要因素有焊接缺陷、接头类型、焊缝形状和残余应力等,量化研究这些影响因素有助于提高焊接结构疲劳强度设计和疲劳寿命预测水平。本论文在铁道部科技开发计划项目“大秦线重载列车基础理论研究一列车载荷谱的试验研究”支持下,着重研究了T型接头焊接根部残余应力和裂纹应力强度因子问题,并将研究成果应用在C70型敞车车体枕梁下盖板与C80型敞车端部支撑梁连接处的疲劳强度研究中。主要工作如下：1、建立了用于残余应力分析的T型焊接接头精细有限元模型,仿真试验研究了焊缝长度、腹板厚度、底板厚度、焊脚长度和焊接角度这五种几何因素对T型焊接接头焊接根部残余应力的影响规律。2、采用奇异单元法建了T型焊接接头焊接根部裂纹的有限元模型,并对模型进行了收敛性检验和有效性验证。研究了裂纹深度比、裂纹形状比、焊脚比和焊接角度这四种几何参数对T型焊接接头焊接根部裂纹应力强度因子修正系数的影响,并建立这四种几何参数与应力强度因子修正系数之间关系的数学模型。3、从统计分析、材料分析、组装分析、断口分析四个方面对C70型敞车枕梁下盖板裂纹进行了分析,实测了枕梁下盖板残余应力、静应力及动应力。将装配间隙分为组装间隙与接触间隙,采用有限元方法,研究了残余应力与组装间隙之间的关系以及静应力、动应力与接触间隙之间的关系。4、基于实测载荷谱,研究了C70型敞车枕梁下盖板裂纹萌生寿命与组装间隙、接触间隙、疲劳强度降低系数之间的关系以及裂纹扩展剩余寿命与组装间隙、接触间隙之间的关系。建立了受残余应力影响的裂纹扩展模型,随着裂纹扩展,研究了裂纹形状比的变化规律,以及不同初始裂纹形状比条件下,裂纹前缘无量纲裂纹扩展速率的变化规律。5、考虑焊接根部存在未焊透缺陷,建立了C80型敞车端部连接处焊接根部裂纹疲劳扩展的仿真模型,研究了实际运行条件下,裂纹扩展剩余寿命与裂纹深度、裂纹形状比、焊脚比、焊接角度之间的关系。更多还原

【Abstract】 Welding is the most important connection method for wagon body structures. However, fracture accidents often occur at welded structure, where90%of accidents are the fatigue failure. The Main factors influences fatigue strength of welded structures, such as weld defects, weld joint types, weld shapes and residual stress. Quantitative study on these factors is benefit for fatigue strength and fatigue life prediction of welded structures.This thesis is supported by the railways development technology develop project "study on basic theory of Daqin line heavy train-experiment study for load spectrum of train". The intensity factors, Residual stress and welding root crack stress, are focused. The research findings are applied in fatigue strength study of C70gondola car body’s sleeper beam cover and also in C80gondola end-supported beam connecting region. The main work involves:1. The refined finite element model of T-butt joint is built for residual stress analysis. The effects of geometry factors on welding residual stress of T-butt joint’s root region are studied. Geometry includes five types, which are weld seam length, web plate thickness, base plate thickness, weld leg length, weld angle.2. The finite element models of T-butt joint’s weld root crack is built by singular element method. The convergence and availability of finite model are tested in this thesis. The effects of crack depth ratio, crack shape ratio, weld leg ratio and weld angle on magnification factors of stress intensity factor is studied, and the mathematical models of relationship between four geometric parameters and stress intensity magnification factors is built.3. C70gondola car body’s sleeper beam cover crack is analyzed by statistic analysis, material analysis, assembly analysis and fracture analysis. The residual stress, static stress and dynamic stress of cover crack are measured. Assembly clearance is divided into composing and contact clearance. The relationship between residual stress and composing clearance and also the relationship among stress, dynamic stress and contact clearance is studied with finite element method.4. The relationship between C70gondola car body’s sleeper beam cover crack initiation life and composing clearance, contact clearance, fatigue strength reducing coefficient and also the relationship between crack growth life and composing clearance, contact clearance are studied with actual load spectrum. The crack propagation model is built under the influence of residual stress. Crack shape ratio and non-dimensional crack growth rate are studied as crack propagation.5. Simulation model of C80gondola end-supported beam connecting region weld root crack is built with the incomplete penetration defect ate welding root. The relationship between crack growth life and crack depth, crack shape ratio, weld leg ratio, weld angle is studied with actual operating condition.更多还原