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类型 基础研究 预答辩日期 2018-04-04
开始(开题)日期 2015-06-10 论文结束日期 2018-01-21
地点 土木楼会议室214(九龙湖校区) 论文选题来源 国家自然科学基金项目     论文字数 9.1 (万字)
题目 铸钢件非对称环形焊缝残余应力分析与断裂性能研究
主题词 铸钢件焊缝,残余应力,焊接数值模拟,金相转变,内表面裂纹扩展
摘要 圆截面钢管结构以其建筑美学和优异的力学性能在大型空间钢结构和桁架公路桥等工程中得到越来越广泛的应用。焊接的钢管相贯节点难以适应现代钢结构的发展,其复杂的连接形式和应力集中严重影响节点的可靠性和安全性。作为一种新型的连接形式,铸钢节点的应用可有效避免焊接节点处复杂的相贯线切割、节点区严重的应力集中和潜在的焊接缺陷;且结构形式简单、受力性能好、避免了复杂的焊缝形状。铸钢节点具有良好的适应性,可以按照实际需要设计成各种复杂形状,优化节点连接形式,改善节点连接区域应力分布,提高结构的安全可靠性。 铸钢构件和主体结构之间的焊缝成为影响结构安全的关键区域。由于构件的制造与设计工艺不同,该处焊缝结构存在非对称的设计特点,即焊缝几何结构不连续性和焊接母材力学性能匹配性问题,而对接焊缝结构壁厚与母材力学性能的差异分别是焊缝几何结构不连续性和强度匹配性问题的重要内容。本课题从铸钢节点与圆截面钢管结构之间的非对称环形焊缝结构出发,以非对称焊缝结构为主要研究对象,对影响焊缝结构力学行为的焊缝几何结构、焊件母材力学性能和材料固态相变方面主要因素,焊缝结构断裂性能和焊接多场耦合数值技术展开了研究。论文以不同工程背景下的非对称焊缝结构为对象,分别对存在焊缝结构几何不连续性和材料力学性能匹配性问题的焊缝结构进行了探讨,致力于该类型焊缝残余应力特性与断裂性能和计算焊接力学数值技术的研究。论文主要研究内容和成果如下: 1. 改进了焊接数值分析理论中焊缝材料填充技术,基于二次开发技术实现移动焊接热源和焊缝材料填充过程的动态模拟,建立焊接数值分析模型,分析了不等厚板对接焊缝结构残余应力与焊接力学行为。在焊缝区设置低材料属性的“完全弹性单元”,参与变形计算,持有真实材料热力学属性的焊缝材料单元,随焊弧的移动而实时激活参与焊接热力学分析,解决了经常出现的因焊弧附近单元高温条件下畸变导致的计算中止问题。将建立的焊接数值模型应用于等厚与不等厚钢板对接焊缝结构焊接力学行为和残余应力分布特点的对比研究,对影响焊缝力学行为的几何不连续性问题进行探讨。研究表明,该类型焊缝的几何不对称性设计导致了焊接残余应力的不对称分布,从而改变了焊缝结构的力学特性,厚度越大,热影响区的残余应力越小。 2. 异种钢材环形对接的多层多道焊缝结构残余应力特点与焊接工艺技术研究。通过焊缝材料单元激活顺序的调整和相应焊弧移动时空坐标的动态设置,实现异种钢多层多道焊缝结构和焊接工艺技术的数值模拟研究。结合异种钢材环形多道焊缝结构分析模型,揭示了异种材料环形焊缝结构焊接残余应力的分布特点及变化规律,结果表明,母材热力学性能的差异导致焊缝两侧残余应力呈非对称分布,在屈服强度较小的焊件一侧形成的焊接残余应力较小。焊接工艺研究表明,环形多道焊缝焊接顺序和焊接起止位置对该类型焊缝残余应力分布的影响明显,优化焊接工艺技术可有效控制焊接应力与变形;且拘束边界条件在焊接变形过程中会形成较大的拘束应力,其焊接应力的变化规律因材料性能的差异而不同。 3. 铸钢节点环形对接焊缝结构焊接残余应力形成与变化机理研究。铸钢构件和主体结构之间的焊缝结构受到几何结构不对称性和焊件母材力学性能匹配性问题的综合影响,尽管工程应用的铸钢材料屈服强度通常相对小于与之焊接的主体结构钢材,且铸钢管壁厚较大,但研究表明,由于不对称的焊缝几何结构设计,导致在其一侧形成较大的轴向残余应力和局部变形。该类型焊缝残余应力形成和变化特点明显不同于普通的焊缝结构,其焊缝力学行为特点受到焊缝几何结构和材料性能的综合影响,较普通焊缝更为复杂。通过多种焊缝结构焊接应力与变形分析,探讨了该焊缝几何结构对焊接力学行为的主导性影响机制,且研究表明,单面V型的焊缝槽口设计可有效减小热影响区的残余应力与影响范围。 4. 发展了焊接过程温度场、材料金相组织转变、焊接应力与变形的多场耦合分析技术,较全面的反映了焊接过程中主要现象之间的作用关系。基于Koistinen-Marburger和Leblond相变动力学模型,以及反映材料相变规律的CCT图,通过二次开发技术,解决了焊接冶金现象中固态相变行为的预测和分析问题,并开发了焊接热力-金相-应力多场耦合分析程序。研究考虑了材料连续加热和冷却相变过程的相变动力学规律,以及相变潜热,相变塑性变形与体积膨胀方面的相变行为。基于S355J2型钢建立的分析模型研究表明,开发的分析模型可结合温度和实时冷却、加热条件对焊缝和热影响区材料的在焊接过程中冶金现象和相变类型进行相应的预测和计算,数值结果得到相关研究结论的验证。提出的分析技术避免了预设相变发生类型,且单纯依靠温度进行插值计算而忽略焊接冶金现象的时空效应,或不考虑相变过程分析模型的局限性,为焊接冶金现象和热应力与变形场的耦合分析提供了一种数值手段。 5. 铸钢构件环形对接焊缝结构断裂性能与残余应力场内表面裂纹扩展行为研究。研究分析了该类型不对称焊缝结构内壁表面裂纹应力强度因子的变化规律和残余应力场条件下内表面裂纹的扩展行为。研究表明,不对称的焊缝几何结构设计和承受载荷变形特点导致其抗断裂能力要低于普通的等壁厚焊缝结构,焊根及邻近区域形成的残余拉应力场和不对称的焊缝结构力学行为共同加剧了内壁焊根附近表面裂纹的扩展,且裂纹主要从内壁向外壁,沿壁厚方向和环向扩展,但沿内壁环形扩展更为明显,该类型不对称焊缝几何结构的力学行为和残余应力特点导致其承载能力降低。
英文题目 RESEARCH OF WELDING RESIDUAL STRESSES AND THE FRACTURE PROPERTIES OF DISSIMILAR GIRTH WELDED JOINT OF STEEL CASTINGS
英文主题词 welded joint of steel castings, residual stress,welding simulation,metallurgy transformation,internal surface crack propagation
英文摘要 Circular hollow section (CHS) structure has been widely used in large-space steel structure and steel-concrete road bridge, because it brings together architecture aesthetics with sustainable mechanical behavior. Welded joints of tubular structure have been shown to be insufficient to the development of modern steel structure. The safety and reliability are significantly affected due to the complicated welded geometry and severe stress concentration. As a new type of joint, the application of cast steel node remove the complex intersecting curve, severe stress concentration and potential welded defect in connection area. Conventional directly welded joint is replaced by cast steel node; Weld seam along the intersecting curves of directly welded joints is simplified as a butt girth welding detail. Furtherly, any complicated joint types can be easily manufactured and the shape can be optimized for the distribution of forces, which improves the fatigue behavior of the whole structure. However, the welded connection between the casting stubs and tubular structure becomes the vulnerable region that determines the safety of the structure. Since the requirement of casting and design techniques, the dissimilar problem exists in such welded joint, that is the discontinuity of geometry and mismatch of applied base materials. The difference of pipe wall-thickness and material properties are the significant content of those problems respectively. The topic of this research is concentrated on the problems of residual stresses profiles subjected to the effect of asymmetrical geometry of welded joint, mismatch of base materials and metallurgy transformation in heat-affected zone, the fracture properties and coupling analysis techonology of welding simulation. Three kinds of dissimilar welded joints with different engineering background are applied to analyze the corresponding sub-problem, respectively. The objectives of this paper is to explore the welding residual stress (RS) profiles and fracture properties in such dissimilar welded joint as well as the simulation technology of computational welding mechanics. Therefore, the main research works and conclusions of this paper can be expressed as follow: 1. The welded material deposition technique is improved in the weld simulation model. Based on the established simulation model, the residual stress profiles and mechanical behaviour in the dissimilar thickness butt-welded joints is explored. “full-elastic element” with low material properties is introduced in welded area and included in mechanical calculation. The filler element with real material properties will be reactived with the moving of weld arc in the thermal- mechanical analysis. The calculation problem due to the element zero volume distortion since the low material parameters in high temperature. Developed welding simulation model is applied to comparatively analyse the mechanical behaviours and residual stresses in the butt-welded joints with similar and dissimilar thicknesses of steel plates. The results explored the effect of weld geomtry on the mechanical behaviour of welded joint. It conducts that asymmetrical welded geomtry in such dissimilar welded joint leads the variation of RS distribution, and causes the change of mechanical properties weld connection. Lower RS occurs in the thicker steel plates in heat-affected zone. 2. The analysis of RS profiles and welding technique in multi-pass girth-welded joint with different base materials. Througthing the adjustment of filler element reaction and definition of welding arc movement with time and space, the analysis of weld technique in multi-pass girth joint is carried out in this work.Based on the simulation model of multi-pass welded joint, it concludes the RS distribtuion and variation mechanism in such dissimilar welded joint. The results reveal that asymmetrical RS distribution is found since the mismatch of base materials. The lower RS occurrs on the welded components with smaller yield strength. The results of weld sequence analysis convinced that the RS in such dissimilar welded joint is definitely influenced by the welding sequences and weld start/stop positions. The welding stress and deformation can be controlled by optimizing the welding techniques. Since the constrained boundary conditions may cause the extral stress in welding, the variation regularity of RS under the influence of external constraints is different due to the mismatch of base materials. 3. The formation and variation mechanism of RS in girth-welded joint between steel castings and circular hollow section structure. Such kinds of dissimilar welded joint is subjected to the combined effects of asymmetrical geometry and mismatch of base materials. Although the cast steel normally applied with lower yield strength and thicker wall-thckness than the selected CHS structure, the results convince that larger axial RS and local deformation are found in steel castings due to the effect of asymmetrical weld geometry.The formation and variation mechanism of RS in such dissimilar welded joint is definitely different from the ordinary welded structure. The mechanical behaviour in welding is more complicated since the combined influence of asymmetrical geometry and dissimilar base material properties. The conlusion is also verified by the exploration of different weld joints. It reveals that single V type welded geometry contributes to decrease the RS and the range of heat-affected zone. 4. A new procedure of thermo-metallurgical-mechanical couple analysis in welding is developed. It reveals the main interaction relationship of welding phenomena. Based on the theory Koistinen- Marburger model, Leblond phase evaluation model and the continuous cooling transformation (CCT) diagram, the problem of solid-state transformation analysis in wedling metallgy phenomena is solved by the proposed method. Furtherly, a coupling thermo-metallurgical -mechanical analysis procedure in welding is developed. The proposed method considers the continuous heating transformation and continuous cooling transformation behavior of materials. The influence of transformation latent heat, transformation plastic deformation and volume expansion are also employed in the proposed couple analysis model. The established model based on S355J2 steel reveals that it can predict the type of metallurgy transformation and phase proportion of materials in weld zone and heat-affected zone in welding phenomena, based on the temperature, heating and cooling conditions in real time. the developed procedure is convinced by corresponding research work. The advantage of the proposed method is that there is no need to predefine the type of microstructural behaviour and phase transformation, and predict the phase proportion merely by interpolating the temperature acroding to the phase transformation model, which ignores the non-uniform and time varying of metallurgy phanomena in welding. It also makes contribution to the existing method that neglects the effect of phase transformation and provides a newly kind of coupling analysis method for the interation of welding metallurgy phenomena, temperature and stress field in welding. 5. Analysis of internal surface crack propagation behaviour in RS field and fracture properties of girth-welded joint between steel castings and CHS structure. The stress intensity factors for internal surface circumferential crack and crack propagation behavior in weld-induced RS field are explored to comprehensively understand the failure mode and fracture resistance of such dissimilar welded joint of steel castings. The results convinced that asymmetrical welds geometry of such dissimilar welded joint leads to weaker fracture resistance than the ordinary weld structure with equal wall-thickness. Both the asymmetrical weld geometry and tensile residual stress contribute to the growth of internal surface crack at welded root in the circumferential direction and radially from inside to outside of the pipe welded joint. The fracture resistance is decreased since the combined effects of residual stress and asymmetrical welds geometry.
学术讨论
主办单位时间地点报告人报告主题
靳慧教授课题组 2013.9.3 逸夫馆607 夏杰 改进和声搜索算法讨论
Noori教授课题组 2013.9.10 逸夫馆607 夏杰 Sensor placement for health monitoring system on large gantry crane structure
Noori教授课题组 2013.11.22 逸夫馆607 夏杰 Brief introduction on an improved harmony search algorithm
靳慧教授课题组 2015.12.8 逸夫馆607 夏杰 Influence of residual stress on fatigue behavior of butt welded joints of cast steel nodes
丁幼亮教授课题组 2016.5.4 土木馆会议室 夏杰 残余应力对铸钢节点环形对接焊缝疲劳性能的影响—进展汇报
靳慧教授课题组 2016.6.4 逸夫馆607 夏杰 环形对接焊缝焊接数值模拟分析与验证
土木工程学院 2015.12.7 东南院101 Sougata Roy Fatigue and fracture of steel bridge infrastructure – a state of the art
土木工程学院 2016.1.5 逸夫馆15楼会议室 Ming L. Wang VOTERS-A platform for continuous network- wide health monitoring of roadways
     
学术会议
会议名称时间地点本人报告本人报告题目
the 12th Word Congress on Computational Mechanics 2016.7.24-29 Seoul, Korea Residual stress analysis of dissimilar multi-pass welded pipe joints considering the influence of welded sequence
江苏省力学学会固体力学专业委员会换届及学术交流研讨会 2016.12.18 南京 异种金属环形对接焊缝焊接残余应力场分析
     
代表作
论文名称
numerical modeling of coupling thermal-metallurgical transformation phenomena of structural steel in
numerical study of welding simulation and residual stress on butt welding of dissimilar thickness of
optimal sensor placement for space modal identification of crane structures based on an improved har
Research of Sensor optimization algorithm for vibration monitoring of crane structure
 
答辩委员会组成信息
姓名职称导师类别工作单位是否主席备注
李兆霞 正高 教授 博导 东南大学
张建 正高 教授 博导 东南大学
丁幼亮 正高 教授 博导 东南大学
刘先斌 正高 教授 博导 南京航空航天大学
王炅 正高 教授 博导 南京理工大学
      
答辩秘书信息
姓名职称工作单位备注
何顶顶 其他 工程师 东南大学