Distribution of Inherent Strains and Residual Stresses in Medium Thickness Plate Weldment

A fundamental theory for the analysis of residual welding stresses and deformation based on the inherent strain distribution along the welded joint is introduced. Distribution of inherent strains and longitudinal residual stresses in medium thickness plate weldment is calculated and analyzed. A new method of calculating inherent strains and longitudinal residual stresses is proposed.     

Distribution of Longitudinal Inherent Strains in Multiple-passes Welding

A fundamental theory for the analysis of residual welding stresses and deformation based on the inherent strain distribution along the welded joint is introduced. The computing method of distribution of longitudinal inherent strains in multiple-passes welding in heavy plate weldment is proposed. Distribution of longitudinal inherent strains in one-pass welding and two-passes welding are compared and analyzed. The effect of cutting on inherent strain is discussed.     

Prediction Models on Distribution of Inherent Strains in T Type Welding Structure

A fundamental theory for the analysis of residual welding stresses and deformation based on the inherent strain distribution along the welded joint is introduced. The method of predicting maximum hardness Hv(y, z) and maximum inherent strain gmax is given     

高强度钢加劲板焊接残余应力测试及分析

为研究高强度钢的板肋加劲板焊接残余应力分布特点,该文利用切割法对板肋加劲板试件进行了应力测试研究,建立了三维实体热弹塑性有限元模型,采用单元生死和动态约束技术模拟焊缝填充和焊接热输入过程,对比分析了高强度钢和普通钢的应力分布特点,比较研究了母板厚度、肋板厚度、肋板间距和高度对焊接残余应力的影响。研究结果表明:板肋加劲板T型接头角焊缝的焊接顺序与残余应力的分布不相关;高强度钢非焊接区域残余压应力小于普通钢;板件厚度和肋板高度是影响高强度钢的板肋加劲板焊接残余应力的主要因素。     

FEM prediction of buckling distortion induced by welding in thin plate panel structures

Welding distortion generated during assembly process has a strongly nonlinear feature, which includes material nonlinearity, geometric nonlinearity, and contact nonlinearity. In order to obtain a precise prediction of welding distortion, these nonlinear phenomena should be carefully considered. In this study, firstly, a prediction method of welding distortion, which combines thermo-elastic-plastic finite element method (FEM) and large deformation elastic FEM based on inherent strain theory and interface element method, was developed. Secondly, the inherent deformations of two typical weld joints involved in a large thin plate panel structure were calculated using the thermo-elastic-plastic FEM and their characteristics were also examined. Thirdly, using the developed elastic FEM and the inherent deformations, the usefulness of the proposed elastic FEM was demonstrated through the prediction of welding distortion in the large thin plate panel structures. Finally, the influences of heat input, welding procedure, welding sequence, thickness of plate, and spacing between the stiffeners on buckling propensity were investigated. The numerical simulation method developed in this study not only can be used to predict welding distortion in manufacturing stage but also can be employed in design or planning stage.     

316L/S32101异种金属焊接接头的显微组织与力学性能研究

目的 研究乏燃料水池用钢板316L与覆板S32101双相不锈钢的焊接性、接头不同区域显微组织特征及接头与母材之间的性能差异.方法 利用氩弧焊接技术对5 mm厚的316L底板与3 mm厚的S32101覆板以搭接的形式进行焊接,利用金相显微镜、扫描电镜、维氏显微硬度仪和电子万能材料试验机对焊接接头的宏观形貌、显微组织以及力学性能进行研究.结果 316L/S32101焊缝组织主要由铁素体基体、晶界树枝状奥氏体以及晶内细小片状奥氏体所组成;316L侧靠近焊缝处存在一个较窄的熔合区,其组织由奥氏体基体和少许细小分散的铁素体组成,而S32101侧靠近焊缝处组织则由粗大铁素体晶粒和沿晶粒边界分布的若干小块状奥氏体组成.从316L母材区到焊缝区,硬度显著增大,而从焊缝区到S32101母材区,硬度变化很小;焊接接头的抗拉强度高达510 MPa,为两侧316L和S32101母材强度的87.9％和88.6％.结论 在焊接电流为240 A和焊接速度为300 mm/min的条件下,可以通过氩弧焊获得成形良好的搭接接头,且接头的力学性能优异.     

Synchrotron diffraction measurement of residual stresses in friction stir welded 5383-H321 aluminium butt joints and their modification by fatigue cycling

This paper presents two‐dimensional information on the residual stresses in 8 mm 5383‐H321 aluminium plates joined by double pass (DP) friction stir welding (FSW). It considers the inherent variability in residual stress magnitudes along 0.5 m lengths of weld pass, and their modification under a sequence of applied fatigue loads. This represents one of a planned series of experiments aimed at illuminating the effects of fatigue cycling on residual stress fields. In this particular case, the magnitudes of the bending fatigue loads (R= 0.1) were chosen to correlate with the measured proof strengths of the weld metal (approximately 160 MPa) and the parent plate (approximately 260–270 MPa). In four‐point bend S–N tests at R= 0.1 on 40 mm wide FS welded specimens of this alloy and plate thickness, these peak stress levels correspond to lives of around 10⁵ cycles and 10⁷ cycles, respectively. Results from the work indicate that significant variability exists among welded plates in peak compressive stress magnitudes (a range of perhaps ?50 MPa to ?140 MPa), although peak tensile stresses were relatively low and more consistent (from around 0 to 30 MPa). Fatigue loading accentuates the peak‐to‐valley stress change and causes an overall translation of the stresses to become more positive. Peak tensile stresses increase several‐fold during fatigue cycling.     

Prediction of welding distortion in butt joint of thin plates

This paper investigates distortions and residual stresses induced in butt joint of thin plates using Metal Inert Gas welding. A moving distributed heat source model based on Goldak’s double-ellipsoid heat flux distribution is implemented in Finite Element (FE) simulation of the welding process. Thermo-elastic–plastic FE methods are applied to modelling thermal and mechanical behaviour of the welded plate during the welding process. Prediction of temperature variations, fusion zone and heat affected zone as well as longitudinal and transverse shrinkage, angular distortion, and residual stress is obtained. FE analysis results of welding distortions are compared with existing experimental and empirical predictions. The welding speed and plate thickness are shown to have considerable effects on welding distortions and residual stresses.     

钛/铝异种合金脉冲激光焊接接头裂纹产生机理

目的 对0.8 mm厚的Ti6Al4V钛合金和2 mm厚的AA6060铝合金薄板进行脉冲激光焊接,分析异种轻合金激光焊接裂纹产生的机理及界面结合机理。方法 采用扫描电镜、EDS能谱以及显微硬度计等微观表征分析方法,对焊接接头的形貌特征、成分以及显微硬度进行分析,探索焊接接头处裂纹产生的原因。结果 钛/铝脉冲激光焊接性较差,接头存在严重的裂纹缺陷,裂纹多集中在焊缝与铝母材交界处以及焊缝中心区域位置,主要以热裂纹为主;接头焊缝可能存在大量的Ti-Al金属间化合物以及少量未熔的钛,其界面层主要成分推测为层状TiAl和外层锯齿状的TiAl3;接头整个焊缝区域的平均显微硬度为HV0.1420,其硬度水平远远高于焊缝两侧铝合金母材,也高出钛合金母材很多。结论 钛铝金属间化合物使钛铝焊接接头焊缝区脆性增大,另外接头焊缝区存在较大的组织应力、热应力、拉压应力、拘束应力等复杂应力,致使焊缝内存在较严重的裂纹缺陷。     

双面双弧焊对高强钢焊接效率和质量影响分析

对高强钢10CrNi3MoV钢厚板进行了双面双弧焊接试验研究。结果表明,焊接长2 m、厚50 mm的钢板,双面双弧焊与传统单弧MAG焊相比,生产效率提高1.4倍,焊接接头力学性能满足指标要求;双面双TIG打底的热影响区金相组织为板条状马氏体,焊缝区为板条马氏体+针状铁素体。     

Utilization of thermo-elasto-plastic analysis of welding eigenstrain for improvement of the bead flush method

Measurement of welding residual stresses is one of important tasks to assess the structural integrity of welded structures. By now, authors have proposed a new nondestructive evaluation method of welding residual stresses called the bead flush method, and confirmed its utility for simple welded plates by numerical simulations and experiments. In this method, eigenstrains are determined by the inverse analysis using released strains measured during removing reinforcement of weld. And then residual stresses are calculated by simple FEM analyses using eigenstrains determined above. For wider applicability and higher accuracy of this method, eigenstrain field should be determined accurately beforehand in the inverse analysis. Therefore, in this paper, a concept how solution sets of eigenstrains are determined in the inverse analysis is proposed. Based on this concept, influencing factors of welding eigenstrains are investigated and relations between welding eigenstrains and residual stresses are made clear by the thermo-elasto-plastic analysis.     

An inverse analysis method to estimate inherent deformations in thin plate welded joints

Weld-induced distortion occurs as an unavoidable consequence due to the intrinsic nature of non-uniform heating and fast cooling. Welding distortion not only negatively affects manufacturing accuracy, but also increases fabrication cost due to straightening work. Past researches suggest that elastic finite element method based on inherent strain theory is an effective approach to estimate welding deformation for welded structures. However, when this method is used to simulate welding deformation in a large or complex structure, the values of inherent deformations in each typical joint must be known beforehand. In the present study, a new method based on inverse analysis was developed to obtain the inherent deformations in typical welded joints. Meanwhile, the influence of weld length on welding deformation was investigated. In addition, using the proposed method, a database of inherent deformations in thin plate butt joints was established.     

Nondestructive Evaluation of Welding Residual Stresses in Dissimilar Welded Pipes

This paper investigates the nondestructive capability of ultrasonic waves in residual stress evaluation of dissimilar welded pipes. Longitudinal critically refracted (L _CR ) waves are employed to measure the residual stresses in a pipe-pipe joint of stainless steel 304 and carbon steel A106. Measuring the acoustoelastic constant is usually accomplished through the tensile test which needs cutting the tested material to extract tensile test specimens. However, cutting the tested pipe to complement the nondestructive ultrasonic measurement was not considered here. Instead, a dissimilar welded plate with the same welding specification, joint geometry, thickness and the same dissimilar materials is used to extract tensile test samples. The measured acoustoelastic constant of the plate along with the measured time of flight of the L _CR wave on the pipe, are utilized for ultrasonic stress measurement. A finite element model of welding process validated by hole-drilling method is used to verify the ultrasonic results. The results show good agreement between finite element and ultrasonic measurements in the pipe measured without any destructive process.     

Influence of the filler metal on the properties of Ti-6Al-4V electron beam weldments. Part I: Welding procedures and microstructural characterization

The use of different procedures for electron beam welding of 17 mm thick Ti-6Al-4V plate and the difficulties found in this process are analysed. When this alloy was welded autogeneously the presence of significant amounts of α martensite was observed, recommending looking for another solution. In the early trials a V joint design was used but distortions and defects were detected in the welds when multi-pass procedures were considered. Consequently, for the remaining weldments K or I joint configurations were selected. Initially, Ti-6Al-4V wire was preferred in order to match mechanical properties with base material but no significant improvement was found leading to consideration of using a less alloyed filler metal. Different commercially pure titanium filler metals have been employed to optimise the performance of the fusion zone of electron beam weldments. In a second paper [1] the influence of the welding procedure on the mechanical properties of the various joints will be discussed.     

PHS1800热成形钢自动化TIG焊接成形特性及工艺优化

目的 研究不同焊接参数下PHS1800热成形钢自动化TIG焊接的成形特性及其工艺优化。方法 利用自动化TIG焊接技术对厚度为1.4 mm的PHS热成形钢板进行焊接,采用金相显微镜、扫描电子显微镜和万能实验机,对焊接接头的熔深、熔宽以及拉伸性能进行测试。结果 随着焊接速度的增大,焊缝熔深从板厚深度(1.4 mm)减小至0.99 mm,焊缝熔宽从8.69 mm减小至5.70 mm;随着焊接电流的增大,熔深从0.85 mm增大至板厚深度(1.4 mm),熔宽从4.52 mm增大至9.83 mm;随着脉冲频率的增大,熔深从0.98 mm增大至1.35 mm,但熔宽变化相差不明显。基于L25(5³)正交实验,确定焊接接头最大拉伸载荷为23.34 kN,其断口为脆性断裂。结论 焊接电流对成形特性影响最大,焊接速度对拉伸性能影响最显著。为了得到成形效果良好的焊接接头,热输入量不宜过高,因此需适当增大焊接速度或降低焊接电流。制备出的焊接接头成形与力学性能均良好,且优化后的工艺参数如下:焊接速度为6 mm/s,焊接电流为116 A,脉冲频率为26 Hz,可为汽车企业实际生产提供一定的理论依据。     

钛铝异质材料插销增强搅拌摩擦点焊接头组织与力学性能

目的开发一种无针搅拌头,以解决传统搅拌摩擦焊产生的匙孔和Hook缺陷问题。方法钛板预制通孔,铝板预制盲孔,插销置于孔中,进行搅拌摩擦点焊。采用无针搅拌头对厚度为2mm的TC1钛合金板和厚度为4 mm的2A12铝合金板(钛上铝下)进行了异种金属搭接搅拌摩擦点焊试验,试验采用旋转速度为950 r/min,焊接时间为100 s,下压量为0.2 mm的工艺参数,对焊接接头的抗拉剪力及接头组织进行评估。结果添加插销获得的焊接接头,钛、铝板与销之间实现固相连接,有效解决了有针搅拌摩擦焊产生的匙孔和Hook缺陷问题,且接头的抗拉剪力达到了6.42 kN。结论提出的插销增强搅拌摩擦点焊的新方法,采用的搅拌头具有较低的制造成本,工艺简单,提高了焊接效率,同时确保了焊接接头的质量。     

Microstructure characteristics of thick aluminum alloy plate joints welded by fiber laser

It's difficult to weld high strength thick plate since the groove is huge when using traditional arc welding, and the weld tends to be softened and large deformation could occur after multi-layer welding. All of these can affect the industrial application of high strength thick plate wielding. In this case, developing advanced welding technology and welding material is necessary to optimize the microstructure and performance of the welds. Fiber laser has many advantages such as good monochrome and high quality laser beam. In order to decrease the heat damage to the base metal from the welding heat source, low heat input is employed for welding thick plate. Fiber laser is applied in the welding of 20 mm thick Al–Zn–Mg–Cu alloy with super narrow gap filler wire. The microstructure comparison of Al–Mg–Mn alloy and Al–Mg–Mn–Zr–Er alloy welded joints reveals that a huge amount of fine equiaxed grains is formed in the weld zone of Zr and Er micro-alloying Al–Mg–Mn alloy welding wire and a great number of precipitation strengthening phases are precipitated in the weld zone after the heat treatment of welded joints in the entirety.     

16MnR钢激光冲击工艺及对焊接结构应力腐蚀性能的影响EI北大核心CSCD

对16MnR母材进行激光冲击工艺实验,获得优化的激光冲击工艺参数。对激光-MAG复合焊焊接接头进行表面处理,分析接头激光冲击前后状态的残余应力分布及抗应力腐蚀性能变化。结果表明:对16MnR钢平板经激光冲击处理后,在材料表面最大可引入475μm厚度的塑性变形层,并同时引入-593 MPa的压应力分布。采用优化激光冲击工艺对16MnR钢焊接接头进行表面处理后,可有效减小焊接接头表面的残余拉应力分布。在3.5%NaCl(质量分数)条件下对激光冲击处理前后的接头试样进行慢应变速率应力腐蚀实验,发现激光冲击处理前后16MnR钢焊接接头的应力腐蚀敏感指数I_(SSRT)分别为0.106和0.104,表明激光冲击可以提高接头的抗应力腐蚀能力。     

Al-Mg合金电子束填丝焊接头的显微组织与力学性能

采用ER5183焊丝作为填充材料,对厚度为2 mm的Al-Mg合金进行真空电子束填丝焊接,并对焊接接头的微观组织及力学性能进行分析测试。结果表明,在合适的焊接工艺条件下,获得的Al-Mg合金接头焊缝成形良好。微观分析显示,接头熔合区为柱状晶和等轴状枝晶组织,主要由α(Al)基体相和β(Al₃Mg₂)强化相组成,焊缝中存在大量的缠结位错和第二相粒子。力学性能测试表明,与母材区的硬度相比,接头熔合区的硬度有所降低。在最佳工艺条件下获得接头的抗拉强度为311.2 MPa,达母材抗拉强度的96.9%。接头拉伸断口表面分布的韧窝数量较多,呈明显的韧性断裂特征。      

焊接工艺参数对Q345钢平板焊接残余应力的影响

为研究焊接工艺参数对Q345钢平板焊接残余应力的影响,对采用药芯焊丝半自动焊接后的8 mm厚平板焊缝结构进行仿真模拟,在经验数值范围内设置不同的焊接工艺参数值,分析平板在横向和厚度方向的焊接残余应力分布情况。研究结果表明:横向的最大焊接残余应力分布在热影响区,且随着焊接速度的增大和焊接层间温度的降低而降低;沿厚度方向的最大焊接残余应力为115.92 MPa,位于平板中间层,随着焊接速度的增大而先减小后增大;平板焊接在横向的残余应力远大于厚度方向的应力。根据焊接残余应力的变化情况,运用二元回归分析法对横向和厚度方向的最大焊接残余应力进行函数拟合与检验,并开展多因素拟合模型的分析,得到焊接速度和焊接层间温度对焊接残余应力的综合影响规律。通过研究残余应力的变化趋势可选定焊接残余应力最小时的工艺参数范围,实现焊接工艺参数优化。