预腐蚀及复杂应力场下钢桥焊接接头疲劳性能研究

发布时间：2018-04-04 04:03

  本文选题：钢桥　切入点：焊接接头　出处：《西南交通大学》2015年博士论文

【摘要】：环境腐蚀和疲劳是影响钢桥耐久性的重要因素,实际工程中钢桥焊接接头大多处于复杂应力状态,因此本文针对预腐蚀及复杂应力场下钢桥焊接接头的疲劳性能展开研究。(1)介绍了疲劳寿命评估方法、多轴疲劳破坏准则以及多轴疲劳试验的研究情况。归纳总结了钢桥腐蚀类型、影响因素、腐蚀预测模型和腐蚀试验方法。阐述了腐蚀疲劳裂纹萌生机理和扩展机理的研究现状,概述了国内外学者对腐蚀疲劳寿命评估的研究进展。(2)参考国内外文献,构造不同倾角(0°、15°、30°、45°)全熔透承载角焊缝十字形焊接接头来模拟正应力和剪应力共同作用下的复杂应力场。采用线性外推、二次外推和1 mm法计算焊接接头的热点应力,根据不同网格尺寸的计算结果来确定合适的网格密度。分析热点正应力集中系数和热点剪应力集中系数随倾角的变化情况。最后,分别采用等效应力法、相互作用方程法和双参数临界面法进行疲劳寿命评估,并与试验结果进行对比分析,推荐采用线性外推法计算热点应力,等效应力法来预测复杂应力场下焊接接头的疲劳寿命。(3)总结了大量的腐蚀坑深度模型,介绍了腐蚀坑缺口和裂纹当量化技术,最终采用最简单的幂函数模型表示蚀坑深度与时间的关系,为了研究当单个蚀坑尺寸对疲劳寿命的影响,把蚀坑当作形状规则的球形缺口来处理,并且考虑两种不同的蚀坑深度。(4)对3种不同腐蚀程度下的45°倾角全熔透承载角焊缝十字形焊接接头进行疲劳试验,得到了它们的S一N曲线。研究不同腐蚀损伤对焊接接头热点应力集中系数和疲劳缺口系数的影响,提出了一种考虑腐蚀深度和应力幅的腐蚀疲劳寿命影响系数定义方式,根据试验结果拟合得到了它的表达式。结果表明蚀坑缺口对焊接接头的疲劳性能有一定影响,但不是很敏感；不同腐蚀深度和应力幅下焊接接头的疲劳强度降低程度不同。(5)以不同腐蚀程度下45°倾角全熔透承载角焊缝十字形焊接接头为研究对象,采用数值方法计算焊接接头表面裂纹的应力强度因子,分析不同蚀坑尺寸、裂纹形状比和裂纹深度对焊接接头应力强度因子的影响规律。结果表明蚀坑深度对应力强度因子的影响起主要作用,蚀坑球半径的影响比较小；裂纹表面点为Ⅰ型开裂,而最深点为Ⅰ+Ⅱ复合型开裂；蚀坑深度、裂纹形状比和裂纹深度对表面点应力强度因子影响大于最深点。(6)根据不同腐蚀程度下十字形焊接接头的S-N曲线计算疲劳裂纹扩展速率公式参数,采用数值方法模拟不同复合型裂纹扩展准则下十字形焊接接头的疲劳裂纹扩展,基于多项式拟合得到了不同复合型裂纹扩展准则下的裂纹形状修正系数,最终采用最大周向应力准则对裂纹扩展速率公式进行修正。给出了不同应力幅和腐蚀程度下有效应力强度因子幅、裂纹扩展角与裂纹深度的关系,裂纹深度与循环次数的关系,对比分析了模拟和实际裂纹扩展路径。结果表明裂纹扩展模拟路径与实际路径符合较好,修正后的裂纹扩展速率得到的疲劳寿命与试验结果吻合较好,基于最大周向应力准则的裂纹形状修正系数能够用于疲劳寿命计算。(7)从损伤力学角度出发提出焊接接头疲劳损伤模型,采用裂纹尺寸来定义损伤变量,给出了两种损伤演化模型：Chaboche模型和Lemaitre模型,结合疲劳试验结果确定了不同腐蚀程度下十字形焊接接头Chaboche损伤演化方程的材料参数,得到了十字形焊接接头的损伤曲线和疲劳寿命预测方程。结果表明裂纹尺寸能够作为焊接接头的损伤变量,Chaboche模型能够用于焊接接头的损伤评估。
[Abstract]:Environmental corrosion and fatigue are important factors affecting the durability of steel bridge, steel bridge welded joints in practical engineering are mostly in the complex stress state, this paper carries out research on the fatigue performance of pre corrosion and complex stress field of steel welded joints. (1) introduced a method to estimate the fatigue life of multiaxial fatigue damage criterion and research multi axial fatigue test. Summarizes the steel corrosion types, influence factors, models and methods for corrosion testing of corrosion prediction. Describes the present situation of the initiation mechanism and propagation mechanism of corrosion fatigue crack, research progress of domestic and foreign scholars on the evaluation of corrosion fatigue life is summarized. (2) refer to the domestic and foreign literature, construct different angle (0 degrees, 15 degrees, 30 degrees, 45 degrees) full penetration weld carrying cruciform welded joints to simulate normal stress and shear stress under the complex stress field. By linear extrapolation, two time extrapolation 1 and the MM method to calculate the hot stress of welded joints, to determine the appropriate grid density according to the calculation results of different mesh size. Analysis of hot spots is the stress concentration coefficient and hot shear stress concentration coefficient changes with angle. Finally, using the equivalent stress method, interaction method and parameters of critical plane method of fatigue life assessment, and the results were compared with experimental results, recommend the use of linear extrapolation method to calculate the hot spot stress, to predict the complex stress field of welded joints fatigue life equivalent stress method. (3) summarized a lot of deep pit corrosion model, introduces corrosion pits and cracks when the gap of quantitative techniques eventually, the exponential function model is the simplest representation of relationship between corrosion pit depth and time, in order to study the effect of a single pit when the size of the fatigue life, the spherical gap pits as shape rules to handle, and the test About two different depth of corrosion pit. (4) of 3 different corrosion degree under the angle of 45 DEG full penetration weld cross bearing fatigue tests of welded joints, the S N curve. They study different corrosion damage effect on stress concentration coefficient and fatigue notch factor of welded joints of hot spot that is put forward by considering the corrosion depth and stress amplitude of the corrosion fatigue life influence coefficient is defined, according to the test results obtained by fitting its expression. The results show that the pit gap has a certain effect on the fatigue performance of welded joints, but not very sensitive; reduce the fatigue strength of welded joints with different corrosion depth and stress amplitude under the different degree. (5) under different corrosion degrees to 45 degrees angle of full penetration weld carrying cruciform welded joints as the research object, the numerical calculation method of welding joint surface crack stress intensity factor analysis Different pit size, crack shape ratio and crack depth on stress intensity factor of welded joints. The results showed that the effect of corrosion pit depth and stress intensity factor plays the main role, effect of pit radius is relatively small; the crack surface point type cracking, and the deepest point is I + II compound cracking; corrosion pit depth, crack shape ratio and crack depth on the surface of the stress intensity factor effect is greater than the deepest point. (6) according to the different corrosion degree of cruciform welded joint S-N curve calculation formula of fatigue crack propagation rate parameters, the numerical simulation of different compound crack propagation of fatigue crack in welded joint shape under the criterion of cross crack shape polynomial fitting obtained for different composite crack propagation criterion correction coefficient based on the maximum circumferential stress criterion of crack growth rate formula is corrected. Given the different effective stress intensity factors stress amplitude and corrosion degree, relationship between the crack angle and the crack depth, the relationship between the depth and the number of cycles to crack, comparative analysis of the simulation and actual crack propagation path. The results show that the simulation of crack propagation path and actual path is consistent with the crack growth rate was revised the fatigue life and the test results are in good agreement, based on the maximum circumferential stress criterion of crack shape correction coefficient can be used for the calculation of fatigue life. (7) from the perspective of damage mechanics, the fatigue damage of welded joint model is proposed, using the crack size to define the damage variable, gives two kinds of damage evolution model: Chaboche model and Lemaitre model, combined with the the fatigue test results of different corrosion degrees of cruciform welded joints of Chaboche material parameters evolution equation of damage is determined by cruciform welded joints The damage curves and fatigue life prediction equations show that the crack size can be used as a damage variable of welded joints, and the Chaboche model can be used for damage assessment of welded joints.

【学位授予单位】：西南交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：U441.4;U445.583
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本文编号：1708283