Mechanism investigation of welding induced buckling using inherent deformation method

Due to the increasing use of thin plates in lightweight welded structure, welding induced buckling may occur in such thin plate welded structure. In this study, welding induced buckling of thin plate welded structure is investigated using the eigenvalue analysis and elastic Finite Element (FE) analysis based on inherent deformation theory, and the mechanism of welding induced buckling is clarified.Bead-on-plate welding is first examined. Measured out-of-plane welding distortion indicates that saddle type buckling is produced after cooling. Eigenvalue analysis shows the computed lowest buckling mode is the saddle type and the corresponding critical force is less than the applied tendon force evaluated by Thermal–Elastic–Plastic (TEP) Finite Element (FE) analysis beforehand. Using elastic Finite Element (FE) analysis in which all components of inherent deformation are used and also considering initial deflection, out-of-plane welding distortion is predicted with high accuracy compared with measurement. It is also concluded that tendon force (longitudinal inherent shrinkage) is the dominant reason of buckling and it determines the buckling mode, and initial deflection and inherent bending are considered to be disturbances which trigger buckling.Later, a thin plate stiffened welded structure with fillet welded joints is examined. Although welding did not induce buckling of plate fields in bending modes in the considered thin plate stiffened welded structure, the whole stiffened welded structure buckles in a twisting mode, while plate panels remain unbuckled. Eigenvalue analysis gives the twisting buckling mode as the lowest buckling mode. However, in stiffened welded structures, not only tendon force (longitudinal inherent shrinkage) but also transverse inherent shrinkage is responsible for buckling. The good agreement between computed and measured out-of-plane welding distortion shows that the elastic Finite Element (FE) analysis using inherent deformation theory is an advantage of the computational approach to predict welding distortion in large-scale and complex welded structure with enough computational accuracy.     

Analysis of residual stress in stainless steel pipe weld subject to mechanical axial tension loading

This paper presents the characteristics of welding residual stresses in circumferentially butt-welded stainless steel pipe by utilizing three-dimensional (3-D) uncoupled thermo-mechanical finite element (FE) analysis method. Moreover, stress variations in welded joints of the pipe under superimposed mechanical axial tension loading are further investigated employing the welding residual stresses and plastic strains obtained from the thermo-mechanical FE analysis as an initial condition. Results show that spatial variations of the welding residual stresses are present along the circumference and a rapid change of the residual stresses exists at the welding start/stop position, hence 3-D FE analysis is essential to accurately simulate circumferential welding of a pipe component. When mechanical axial tension loading is applied to the circumferentially butt-welded stainless steel pipe, bending moment is generated at the welded joints caused by the circumferential shrinkage of the weld region during welding; thus affecting the axial and hoop stress evolutions in the course of the superimposed mechanical loading.     

Experimental and numerical investigations on residual stresses in a multi-pass butt-welded high strength SM570-TMCP steel plate

During fusion welding process, complex thermal stresses are inevitably generated. The presence of residual stresses can be detrimental to the integrity and the service behavior of the welded part. In this study, both an experiment and a finite element (FE) method were utilized to investigate residual stress distribution in high strength SM570-TMCP (thermo-mechanical controlled process) steel weldment, which was constructed using a multi-pass butt welding process. Firstly, experiments which included a tensile test at elevated temperatures, an observation of the microstructures and a residual stress measurement were carried out to examine characteristics of residual stresses in the weldment. Secondly, a three-dimensional thermo-mechanical FE model was developed to simulate the temperature field and the residual stress field incorporating the experimental results. The thermo-mechanical model used as well as the experimental procedure is described in detail, and the results obtained from the FE model are compared with the experimental measurements and discussed.     

On the prediction of effect of direction of welding on bead geometry and residual deformation of double-sided fillet welds

The present study describes how the effect of direction of welding is useful to minimize distortion in submerged arc welded double-sided fillet joints. In present work, angular distortion of 12 mm thick double-sided fillet welds was measured for same direction and reverse direction welding. It has been observed that the maximum magnitude of the angular distortion for reverse direction fillet welding is lower. Thermal history in horizontal and vertical plate of fillet welds was also measured for both same direction and reverse direction welding. After welding, the fillet welds were sectioned, polished and etched to measure the effect of direction of welding on weld bead geometry. To predict the temperature distribution and thermal history, a finite element (FE) elasto-plastic thermo-mechanical model has been developed for submerged arc welded double-sided fillet welds by using moving distributed heat source. The three-dimensional FE thermal model was verified by comparing peak temperature obtained with experimental values. The model results matched fairly well with experimental results with a variation of 6 percent for sample 1 and 7.5 percent for sample 2 for the maximum values of distortion, and a variation of 2-8 percent for peak temperatures in horizontal plate and 9 percent in web plate.     

Fatigue strength evaluation of welded structural details in corrugated steel web girders

Fatigue strength evaluation of welded structural details is of practical significance in the design of corrugated steel web girders in highway bridges and industrial structures. In this paper, the fatigue strengths of corrugated steel web girders with several welded structural details and welding methods are analytically examined by fatigue tests of corrugated web beams and small-size welded joints. The stress concentration & distribution characteristics of corrugated web beams were analysed using finite element analysis. The beam test results showed that the structure with scallops or notches in the flange has lower fatigue strength and that with butt joints is prone to suffer from shear crack on the corrugated web. Within the inside range of the scallop, the stress concentration becomes greater with the increase of scallop radius and the tension flange contributes significantly to the bending capacity of corrugated steel web beams. The tests for small-size welded joints indicated their applicability in the analysis and prediction of S-N relationship of the test corrugated steel web beams. Finally, the fatigue crack propagation lives of weld joints were compared with those of test corrugated steel web beams with respect to related design Categories of the AASHTO LRFD Bridge Design Specifications.     

Design proposal of butt welded joints of high strength steel considering mismatch ratio and softened zone

针对高强度结构钢在焊接热循环作用下热影响区域可能产生软化现象，且高强钢焊接时将遇到焊材强度匹配的问题，基于高强钢对接焊缝的试验研究、数值分析和理论研究的结果，对考虑焊接软化和焊材强度匹配的强度模型进行简化，进而提出便于设计的简化公式。通过对试验数据、欧洲规范EC3预测值、强度模型预测值和简化公式预测值的对比，得出强度模型和简化公式对接头强度的预测值较为准确，而欧洲规范EC3高估了对接接头强度。为了进一步地将简化公式应用于工程设计，通过搜集和汇总焊缝加工尺寸、高强钢力学性能以及试件实际的工作性能等三方面的数据，对简化公式进行可靠度分析，当安全系数为4.5时，抗力分项系数取为0.84。对我国规范中高强钢对接焊缝连接的设计方法提出设计建议，即在对接焊缝受拉承载力计算式中考虑接头的综合强度，该综合强度取决于钢材强度、焊材强度、软化区情况和约束情况。     

考虑匹配比和软化效应的高强钢对接焊缝的设计建议

针对高强度结构钢在焊接热循环作用下热影响区域可能产生软化现象,且高强钢焊接时将遇到焊材强度匹配的问题,基于高强钢对接焊缝的试验研究、数值分析和理论研究的结果,对考虑焊接软化和焊材强度匹配的强度模型进行简化,进而提出便于设计的简化公式。通过对试验数据、欧洲规范EC3预测值、强度模型预测值和简化公式预测值的对比,得出强度模型和简化公式对接头强度的预测值较为准确,而欧洲规范EC3高估了对接接头强度。为了进一步地将简化公式应用于工程设计,通过搜集和汇总焊缝加工尺寸、高强钢力学性能以及试件实际的工作性能等三方面的数据,对简化公式进行可靠度分析,当安全系数为4.5时,抗力分项系数取为0.84。对我国规范中高强钢对接焊缝连接的设计方法提出设计建议,即在对接焊缝受拉承载力计算式中考虑接头的综合强度,该综合强度取决于钢材强度、焊材强度、软化区情况和约束情况。     

Experimental and FE analysis of submerged arc weld induced residual stress and angular deformation of single and double sided fillet welded joint

Submerged arc welding is well-known for its very high deposition rate and thus the capability to join very high thickness metal pieces in large structural applications. Fillet joints are mostly used in structural applications which can be extensively seen in shipbuilding, bridge construction, house buildings, automobile or any other large structures. Thermal stresses generates in a fusion welded joint due to high temperature gradient, which is the cause of the residual stresses upon cooling followed by the angular deformation and failure of the welded structure. As an effect of the thermal gradient, the induced longitudinal, transverse residual stress & angular distortion can vary in single sided and double sided submerged arc welded fillet joints, during designing & manufacturing welded structures which should be taken into account. The main objective of this paper is to quantify the amount of residual stresses and angular deformation in a fillet welding joint. An elasto-plastic thermomechanical model has been developed for predicting residual stresses. A comparison of the residual stress and angular deformation between single and double sided fillet weld joint has been made. The simulation results reveal that the amount of residual stress present in the single sided fillet weld is more and unbalanced in both side of the center of weld line compared to the double sided fillet weld and the predicted results have been matched with the experiments as well as published literatures.     

九江长江大桥横隔板制造安装施工技术

本桥横隔板为实腹式构造。由上、下两块组成,上接板与下接板直接对接。板单元制造时上接板与顶板一起组焊,梁段组装时,上接板与下接板间采用熔透对接的方式连接。钢箱梁横隔板制作发展从搭接型式开始,相继出现了全断面仰焊型式及横向熔透对接型式。根据横向熔透对接型式横隔板的结构特点,通过对横隔板下接板采用二次切割、上接板模块定位、上下接板连接采用工艺导向板定位、焊接工艺优化及配套工装完成横隔板的制作和安装,在桥梁界率先提出了一套完整的创新工艺技术。     

Numerische Analyse geschweißter Verbindungen von Duplexstahl und Quarzglas

Numerical analysis of welded joints between duplex steel and quartz glass. Welded joints are a vital element in structural engineering. Originating from conventional carbon steel welding in construction, recent advancements in welding technology now allow the joint of modern high‐strength steel and glass materials. With today's methods, an analysis of the welded joints' structural behaviour can be conducted by experiment, as well as by numerical analysis. Particularly for the numeric analysis, capturing the non‐linear thermal and mechanical properties of the materials is important, in order to allow a realistic determination of temperature, microstructure and residual stresses for different types of joints. Simulations of multi‐layered weld joint on duplex steel show, that a targeted heat treatment during MAG‐welding by variation of the welding parameters achieves a beneficial ratio between ferrite and austenite which, for example, ensures a high resistance of the weld to corrosion. The material quartz glass can generally be welded as butt‐weld with a CO₂‐laser. The simulations of a welded joint of a plate and a pipe show, that an optimization of the welding technology of preheat laser beam and welding laser beam is necessary, in order to reduce the thermal impact during the welding process, as well as residual stress in the joint. At the Department of Steel Structures at the Bauhaus‐Universität Weimar, numerical simulations of welded joints between steel and glass materials are a current and topical research focus.     

Q690D高强钢焊缝连接疲劳性能试验研究

文中对Q690D高强度钢材及其焊缝连接的疲劳性能进行试验研究,讨论Q690D母材、对接接头、十字接头三种连接形式的疲劳极限;拟合了S-N设计曲线,并与现行规范进行比较,对其疲劳特性及疲劳寿命给予评价。试验结果表明：Q690D母材与普通钢材相比表现出较高的疲劳抗力;GB50017设计曲线能较好评估循环次数大于30万对接接头的疲劳寿命,且具有足够安全储备;十字接头S-N设计曲线与AISC360规定的疲劳设计曲线吻合较好。采用电镜扫描分析不同阶段断口的微观形貌特征,并基于零塑性累积应变率假设得到疲劳损伤公式,讨论焊接缺陷对试件疲劳损伤的影响。断口形貌可以反映试件的疲劳损伤发展过程,损伤曲线又很好地解释了断口的形成机理。     

钢筋HRB400闪光对焊接头应力腐蚀研究

针对HRB400钢筋闪光对焊接头的应力腐蚀过程进行研究.首先进行环境试验,然后对以下5组试件进行力学性能测试:钢筋母材、钢筋母材21 d5%NaCl溶液侵泡、原始闪光对焊接头、机械加工去除焊接余高的对焊接头、机械加工去除焊接余高的对焊接头21 d5%NaCl溶液侵泡及未去除焊接余高的对焊接头21 d5%NaCl溶液侵泡;并结合有限元模拟分析,最终发现焊接过程使对焊接头产生较大的应力集中,在腐蚀环境下成为混凝土中钢筋性能下降的重要原因.对比试验显示,在焊接区域和焊接夹具的位置,应力腐蚀裂纹更有可能出现.研究结果表明,必须严格控制钢筋生产的工艺过程,并有效防止腐蚀介质的侵蚀,以保证建筑物的长期安全使用.     

Procedural influences on non-linear distortions in welded thin-plate fabrication

Fusion welding is the most common and convenient method used for the fabrication of large, thin-plate welded structures. However, the resulting tendency to out-of-plane distortion exacts severe design and fabrication penalties in terms of poorer buckling performance, lack of fairness in external appearance, poor fit-up and frequent requirements for expensive rework. This study forms part of a long-term project that has the aim of modelling welding and related fabrication processes computationally with particular emphasis on the out-of-plane distortion outcomes. Throughout the present work the computational models have been cross-referenced to realistic experimental test cases. A repeated finding of the trials was that minor variations in fabrication procedures, were found to have significant effects on distortion. In particular, the pre-fabrication procedures, including spot and tack welding, have a significant effect on the initial out-of-plane distortion leading to differences in distortion of the post-welded structures. The support and clamping conditions during welding and cooling of welded thin-plate structures were also found to have a considerable influence on the final predicted out-of-plane distortion. The outcomes often result in different buckling instability behaviour. This paper concentrates on these aspects and draws on studies of buttwelding between plates of thicknesses 3–8 mm.     

赞比亚硫酸贮罐底板焊接变形的控制技术

硫酸贮罐底板直径大、焊缝多、焊接量大,在焊接过程中将不可避免地产生焊接应力和焊接变形。焊接残余应力和变形的存在,会对焊接底板的承载能力和外形尺寸产生不同程度的影响。采用焊接变形控制技术后,可减少底板焊后的变形,释放焊接残余应力,改善焊接质量。自投产以来,至今运行状态良好,实践证明:这种技术方案能满足施工技术要求。     

Optimization-improved thermal–mechanical simulation of welding residual stresses in welded connections

This paper presents a novel computer-aided computational framework to determine the optimum shape parameters in a welding heat source model using a coupled supervised Gaussian process regression (GPR) and genetic algorithm (GA) approach in estimating the welding residual stresses. The experimental X-ray diffraction (XRD) approach validates the optimization-improved thermal–mechanical simulation method. The validation of the proposed approach includes the welded plates with simple geometry to welded pipe-to-plate and the circular hollow section joints with complex topologies. The optimization-derived shape parameters in a welding heat source model lead to close estimates of the temperature history and the welding residual stresses for these types of welded joints considered in this study.     

基于等效结构应力的钢框架焊接梁柱节点低周疲劳评估

在地震作用下钢框架梁柱焊接节点会发生低周疲劳现象,进而导致结构发生破坏。本文基于等效结构应力法提出一种高层钢框架梁柱焊接节点低周疲劳评估方法。首先,结合有限元多尺度模拟方法,建立包含翼缘及腹板焊缝细节的钢框架梁柱焊接节点多尺度模型。其次,利用不同单元尺寸多尺度模型,验证结构应力的网格不敏感特性,进而通过等效结构应力法评估钢框架梁柱焊接节点的疲劳寿命。结果表明,采用等效结构应力法可消除网格的敏感性,在往复荷载作用下,靠近工艺孔焊缝应力水平高于远离工艺孔焊缝,翼缘中心焊缝寿命最低,裂纹最先产生于翼缘焊缝中心处,评估方法为实际工程提供技术支持。     

基于细观损伤力学的梁柱焊接节点断裂破坏预测分析

应用细观损伤力学模型预测分析单调荷载作用下梁柱焊接节点的裂纹萌生与扩展。分别依据节点部位的母材、热影响区和焊缝金属缺口试样的单轴拉伸试验，标定材料细观损伤力学模型的参数；通过有限元分析模拟，预测焊接节点的开裂位置以及断裂破坏的过程，与已有试验结果以及基于微孔扩展模型和应力修正临界应变模型的有限元分析结果相比，建议的细观损伤力学模型的有限元分析结果具有更好的预测精度；针对不同焊接孔几何形状对节点断裂性能的影响进行有限元分析，结果表明，孔的几何形状对节点的断裂破坏模式的影响显著，长圆孔比圆孔具有更好的节点延性，开裂延缓，但是两种孔形的节点承载力差别很小。     

不同断裂模型在钢结构断裂破坏预测中的比较

为对比分析不同断裂模型在钢结构断裂破坏预测中的适用性,选取3类典型的断裂模型（微孔扩展模型、GTN模型、连续损伤模型）对钢结构的断裂破坏进行预测分析。首先基于试验数据标定了Q345钢材以及焊缝金属的断裂模型参数,然后将这3类断裂模型通过ABAQUS的用户子程序嵌入到有限元分析程序中,最后将这3类模型应用到开孔板以及梁柱焊接节点的断裂破坏分析中。结果表明:3类模型均能很好地预测开孔板和节点裂纹的起始和发展过程;3类模型对于开孔板断裂位移的预测精度相当,但对于相对复杂的梁柱焊接节点,GTN模型对裂纹起始位移的预测精度明显高于其他2类模型。     

高性能桥梁钢典型焊接接头疲劳性能试验研究

针对Q500qE高性能钢两种典型焊接接头,包括对接焊缝和横向角接焊缝,设计疲劳试件。其中对接焊试件包括两种形式,分别为板厚56mm和8mm的对 接焊试件;横向角接焊缝试件的主板厚56mm、附连件厚20mm。对三组试件进行了有限元分析,掌握了试件的应力分布状况及薄弱环节,验证了试件设计的合 理性。随后针对三组试件展开了疲劳试验,掌握了不同类型焊接接头的破坏位置及破坏形式。根据试验结果拟合出了三组试件的S-N曲线,并与普通钢的疲 劳性能进行比较,表明Q500qE高性能钢的这两种典型焊接接头的疲劳强度略高于普通钢。采用目前规范规定的疲劳强度容许值进行抗疲劳设计是合理可行的,并且具有足够的安全余量。     

焊接空心球节点焊缝区拉裂和极限承载力分析

焊接节点受拉力作用易在焊缝区断裂,以焊接空心球节点为例在弹塑性非线性有限元分析基础上,分别采用等效塑性应变(EPS)准则和VC准则判断失效的材料单元,以模拟节点拉裂现象。由于球面焊趾处应力、应变集中显著,应力状态复杂,使得钢材脆性程度提高,加快破坏过程,建议采用VC准则反映应力状态对断裂的影响,确定节点的极限承载力。分析结果表明,在不考虑焊缝缺陷的情况下,EPS和VC准则计算的极限承载力数值相差仅3%左右,但是得到的断裂破坏进程不同。