对接接头焊趾应力集中有限元分析

研究焊缝几何参数对应力集中的影响,对于提高焊接结构疲劳强度有重要的意义.本文采用有限元方法,计算了双侧对称加强高和单侧加强高的对接接头焊趾处的应力集中系数,分析了几个主要参数,包括焊趾倾角、焊趾过渡圆弧半径和板厚对于应力集中系数的影响,研究了焊趾处应力集中沿板厚方向的变化情况,在分析大量计算结果的基础上给出了估算两种形式的对接接头应力集中系数的经验公式.结果表明,减小焊趾倾角,增大过渡圆弧半径,可以减缓焊趾处截面形状的变化,改善焊趾处的应力集中;板厚的增加使得应力集中系数增大.并且单侧加强高的对接接头应力集中系数小于双侧对称加强高对接接头的,其减小幅度只与θ有关.     

T型焊接结构的角变形控制

T型焊接在船舶结构中的应用是非常广泛的.T型接头附近局部的加热及冷却使被焊结构产生残余应力及角变形.目前在船厂精度控制中,通常采用构件焊接后对某些部位进行火工校正的方法来控制残余角变形.论文提供了另外一种有效控制结构残余角变形的方法:对结构焊前施加弹性的反向角变形.文中首先利用热弹塑性有限元来模拟未施加反变形的结构的焊接过程,以估算残余角变形;然后模拟施加了弹性反变形的结构的焊接过程,并计算此时结构的残余角变形,以最终确定构件所需要的弹性反向角变形值.施加了弹性反向角变形的构件在焊接后无需进行火工校正.     

Size effect on residual stress in low transformation temperature welded joints

It has been reported that low transformation temperature (LTT) weld metals are beneficial to generation of compressive residual stress around weld zone. In this study, the relationship among residual stress, size effect of LTT welded joints with different plate width and thickness as well as martensite start (Ms) temperatures was investigated by experimental and finite-element analysis. It was found that heat dissipation and thermal expansion coefficient of LTT weld metal had a significant impact on residual stress. Welded joint with a small plate width led to greater compressive residual stresses in the LTT weld, which was due to the lower heat dissipation and smaller thermal expansion coefficient of the LTT weld metal in due course of cooling process. Additionally, the finite-element analysis revealed that increasing plate width mainly affected the longitudinal residual stress, while increasing the plate thickness influenced all the residual stress components in the LTT weld. Furthermore, the LTT weld with a lower Ms temperature of 191 °C resulted in greater compressive residual stresses, and was less sensitive to the LTT joint size, as against the Ms temperature of 398 °C.     

肘板趾端表面裂纹在随机波浪载荷作用下的疲劳扩展预报

肘板趾端是船舶与海洋结构的疲劳热点。文章用三维有限元分析了趾端表面裂纹应力强度因子修正系数的变化规律,并与BS7910推荐的典型节点表面裂纹应力强度因子公式计算结果作了对比,结果表明趾端表面裂纹应力强度因子沿深度方向的放大系数和T型节点相差很小,而表面端点应力强度因子修正系数则当裂纹长度在肘板厚度范围内时和T型节点相差很小,超出后则相差较大。以某客滚船上肘板趾端应力范围长期分布服从Weibull分布,产生系列均值为零的应力幅,应力强度因子分别采用有限元结果和BS7910中T型接头公式进行计算,采用单一曲线模型计算该趾端表面裂纹的裂纹扩展。计算等效应力强度因子幅时,考虑焊接残余应力的影响。计算结果表明以T型接头的公式计算趾端表面裂纹应力强度因子和有限元结果相差很小。建议将T型节点表面裂纹应力强度因子计算公式用于趾端表面裂纹应力强度因子的计算,并采用单一曲线模型对随机波浪载荷下作用下船舶典型节点疲劳裂纹的扩展寿命进行了预报。     

超声冲击处理对高强钢焊接接头残余应力影响的数值模拟

超声冲击处理(UIT)是一种有效的焊后改善焊接接头疲劳性能的工艺措施,其借助机械撞击和超声振动的共同作用,使焊趾表面产生塑性变形从而引入有益的压缩残余应力。为评价UIT技术对焊接接头残余应力的影响,该文提出了一套新的数值分析方法,包括焊接数值模拟及随后的超声冲击处理过程的动态弹塑性有限元分析。在有限元模型中考虑了实际的工艺参数和超声促成的材料软化效应。以船用高强钢AH36非承载十字焊接接头为研究对象,将预测的超声冲击处理前后的残余应力分布与实验结果进行对比,两者有较好的吻合。在此基础上,探讨了静态预载荷对超声冲击处理态残余应力再分布的影响。     

Stress magnification effect of initial deformation on the notch stress field and fatigue strength of thin plate welded joints

Compared with thick plate welded joint, the welding joint of thin plate will produce initial deformation due to its low bending rigidity. The existence of initial deformation will cause the welded structure to produce secondary bending effect, which will produce greater stress magnification effect at the weld toe and seriously affect the fatigue strength of thin plate welded joints. Therefore, based on the correction formula of thick plate, considering the influence of initial deformation and geometric nonlinearity of thin plate, this paper deduces the stress magnification factor formula at the weld toe of T-shaped and cruciform specimens. The accuracy of the revised formula is further verified by comparing the notch stress calculated by the modified formula with the FE results. Finally, the modified formula is applied to the notch stress and fatigue evaluation of typical thin plate welded joints respectively. The results show that the proposed notch stress calculation formula can fully consider the stress amplification effect of thin plate structure, and can be used to quickly evaluate the notch stress field and fatigue strength of thin plate welded joints.     

Influence of tacking sequence on residual stress and distortion of single sided fillet submerged arc welded joint

Submerged arc welding (SAW) is advantageous for joining high thickness materials in large structure due to high material deposition rate. The non-uniform heating and cooling generates the thermal stresses and subsequently the residual stresses and distortion. The longitudinal and transverse residual stresses and angular distortion are generally measured in large panel structure of submerged arc welded fillet joints. Hence, the objective of this present work is to quantify the amount of residual stress and distortion in and around the weld joint due to positioning of stiffeners tack. The tacking sequence influences the level of residual stress and proper controlling of tacking sequences is required to minimize the stress. In present study, an elasto-plastic material behavior is considered to develop the thermo mechanical model which predicts the residual stress and angular distortion with varying tacking sequences. The simulated result reveals that the tacking sequence heavily influences the residual stress and deformation pattern of the single sided fillet joint. The finite element based numerical model is calibrated by comparing the experimental data from published literature. Henceforth, the angular distortions are measured from an in-house developed experimental set-up. A fair agreement between the predicted and experimental results indicates the robustness of the developed numerical model. However, the most significant conclusion from present study states that tack weld position should be placed opposite to the fillet weld side to minimize the residual stress.     

Weld toe versus root fatigue failure mode and governing parameters: A study of aluminum alloy load-carrying fillet joints

In load-carrying fillet welded connections, two fatigue failure modes are possible i.e. weld toe cracking and weld root cracking. The fatigue life associated with weld root cracking is typically much lower than weld toe cracking, exhibiting a wider scatter band, especially for welded aluminum alloys. This paper examines fatigue failure mode transition behaviors in load-carrying fillet welds made of aluminum and their governing parameters, among plate thickness, weld penetration, joint misalignment, weld material, and ultrasound impact peening(UIP). Through both experimental and theoretical studies, a quantitative fillet weld sizing criterion was proposed for avoiding weld root cracking in fillet-welded aluminum connections.     

定位焊顺序对单面埋弧焊接头残余应力和变形的影响（英文）

Submerged arc welding(SAW) is advantageous for joining high thickness materials in large structure due to high material deposition rate. The non-uniform heating and cooling generates the thermal stresses and subsequently the residual stresses and distortion. The longitudinal and transverse residual stresses and angular distortion are generally measured in large panel structure of submerged arc welded fillet joints. Hence, the objective of this present work is to quantify the amount of residual stress and distortion in and around the weld joint due to positioning of stiffeners tack. The tacking sequence influences the level of residual stress and proper controlling of tacking sequences is required to minimize the stress. In present study, an elasto-plastic material behavior is considered to develop the thermo mechanical model which predicts the residual stress and angular distortion with varying tacking sequences. The simulated result reveals that the tacking sequence heavily influences the residual stress and deformation pattern of the single sided fillet joint. The finite element based numerical model is calibrated by comparing the experimental data from published literature. Henceforth, the angular distortions are measured from an in-house developed experimental set-up. A fair agreement between the predicted and experimental results indicates the robustness of the developed numerical model. However, the most significant conclusion from present study states that tack weld position should be placed opposite to the fillet weld side to minimize the residual stress.     

轴力作用下X型焊接管节点热点应力的分布规律

海洋平台中的焊接管节点的疲劳寿命是由热点应力的大小和分布决定。热点应力的大小决定了管节点在疲劳失效前所能承受的循环荷载的次数,而热点应力的位置则决定了疲劳裂纹的萌生位置和扩展方式。文中采用有限元方法分析了承受轴向拉力作用的X型焊接管节点在焊缝周围的热点应力的分布情况,通过对112个X节点进行的模型分析,研究了节点几何参数对热点应力大小和分布规律的影响。     

Measurements and statistical analysis of fillet weld geometrical parameters for probabilistic modelling of the fatigue capacity

Welded joints are commonly used for various structures such as civil engineering infrastructures or marine and submarine structures. It is well known that the geometry of the joints has an important influence on the stress concentration factor and thus on fatigue lifetime. Non-Destructive controls during welding work allow to keep parameters inside bounds and to satisfy quality requirements. However, the effect of the geometry characteristics within these bounds on the structural lifetime needs for a statistical analysis and a probabilistic modelling on the one hand and for a specific computational method on the other hand. When considering the first point, only few works have been carried out on the statistical analysis of the geometrical parameters of a welded joint. The measurement of the different parameters of this geometry is a long and scrupulous work. Recently, some laser process allows obtaining a significant quantity of trajectories along a welded joint for these geometrical parameters. This paper aims at analysing these trajectories for reliability purpose. This laser process allowed us to measure the width of the weld, the angle at the junction between weld and welded component and the radius at the weld toe. The study was completely performed for the two first but it was shown that the assessment of the radius remains challenging.     

轴力作用下T节点焊缝周围的平均应力分布

平均应力模型法是评价海洋平台中管节点疲劳寿命的一种方法,这种方法认为节点的疲劳寿命是由热点应力幅值和焊缝周围的应力分布确定的。管节点焊缝周围应力分布通过一个平均应力分布参数AVS描述。本文研究了轴力作用下T节点的AVS大小,通过对127个不同几何参数的T节点模型的计算,调查了几何参数对AVS的影响,提出了用于计算AVS的参数方程,从而完善了传统的平均应力模型,为轴力作用下T节点的疲劳寿命计算提供了一种快速而高效的方法。     

The effect of weld residual stress on fracture toughness at the intersection of two welding lines of offshore tubular structure

Due to the spatial complexity and fabrication characteristics of offshore platforms, it is inevitable to encounter overlaps or proximity of weld lines in tubular joints. Several international standards such as American Petroleum Institute (API), American Welding Society (AWS), and American Institute of Steel Construction (AISC) regulate the minimum distance between primary weld beads; however, any logical and detailed background of this limitation has not been presented. For a non-compliant weld joint where the regulation is not met, fracture toughness calculation is a typical index to verify the structural integrity.This research consists of two parts. First, weld residual stress distributions are calculated by a 3D thermo-mechanical nonlinear Finite Element Analysis. Two crossing welds, a T-weld crossing on a butt weld, are simulated in one model. A separate tee and a butt welding simulations are also performed for a comparative purpose. Second, SIFs and J-integral values are calculated at the surface and deepest crack tip locations for four different types of semi-elliptical surface cracks. Four cracks are embedded into the weld model and the residual stress distribution from the 3D thermo-mechanical FEA are mapped to a 3D FE crack model as initial conditions. An additional axial tensile load is also imposed. SIF values are compared with those using the weighting function method for the butt weld model subject to three load cases, i.e., tensile stress only, weld residual stress only, and both of them. From the simulation, a tubular joint containing a chord girth weld intersected with weld beads of brace is found to show lower the SIF values than that having only a girth weld on chord.     

基于形函数插值理论预测轴力作用下T型管节点热点应力的分布规律

海洋平台中管节点的疲劳寿命由焊缝周围热点应力的分布情况决定.该文采用有限元方法分析了承受轴向力作用下T节点焊缝周围的应力分布规律.通过对140个具有不同几何形状的T节点模型的有限元分析结果.提出了一种基于形函数插值理论的方法预测T节点焊缝周围的应力分布,并且通过比较插值法得到的结果和有限元结果进行比较,验证了这种方法的准确性.     

确定焊接反变形的数值模拟及规律分析

焊接接头附近局部的加热及冷却使被焊结构产生残余应力及角变形.目前在船厂精度控制中,通常采用构件焊接后对某些部位进行火工校正的方法来控制残余角变形.文章提供了另外一种有效控制结构残余角变形的方法:对结构焊前施加弹性的反向变形.利用热弹塑性有限元法来模拟结构的焊接过程,并对不同板厚、不同热源的结构分别进行数值模拟,最终确定焊接结构的弹性反变形规律:焊接前施加弹性反变形的结构在焊接后角变形趋于零.     

Residual stress measurement in an extra thick multi-pass weld using initial stress integrated inherent strain method

Residual stresses existing in a multi-pass butt joint with a thickness of 70 mm, using a flux-cored arc welding process, were measured by an inherent strain method (ISM). Since such a thick plate before welding contains a large amount of initial residual stresses (−300 to +100 MPa), the initial stresses were integrated with conventional ISM in order to determine the total residual stresses in a welded joint. Two methods named as initial stress integrated ISM and initial inherent strain integrated ISM were suggested for the consideration of the initial stress distributions through the thickness of base plates. The results show that there is a significant difference between the integrated ISM with initial stresses or initial inherent strain and the conventional ISM without initial stresses. The residual stresses measured by any of the initial stress integrated ISM and initial inherent strain integrated ISM agreed well with the neutron diffraction measurement. Thus, the proposed initial stress integrated ISM is a proper destructive measurement method in the case of thick weld joints.     

一种复杂载荷作用下船舶结构疲劳裂纹扩展预报方法

风暴模型是Tomita等提出的用来评估船舶结构疲劳强度的一种随机波浪载荷简化模型,它能表达波浪载荷是与时间相关的随机过程。文中介绍了风暴模型及波浪诱导应力短期分布的基本特征。将风暴模型和裂纹扩展率单一曲线模型及焊趾表面裂纹应力强度因子的计算方法结合起来,探讨了复杂载荷作用下船舶结构疲劳裂纹扩展预报方法。并用权函数法计算了给定残余应力分布的表面裂纹应力强度因子。预报了对接焊接接头焊趾处表面裂纹在风暴波浪载荷作用下的疲劳裂纹扩展行为,结果表明风暴的大小、顺序,初始裂纹尺寸及残余应力对裂纹扩展行为影响明显。合理的风暴模型参数及初始裂纹尺寸的确定对船舶结构的疲劳寿命预报是非常重要的。     

Geometric stress distribution along the weld toe of the outer brace in two-planar tubular DKT-joints: Parametric study and deriving the SCF design equations

Regarding the research efforts expended so far on the calculation of stress concentration factors (SCFs) in tubular joints, two major shortcomings can be noted: (a) significant effort has been devoted to the study of SCFs in various uni-planar connections. Nevertheless, for multi-planar joints which cover the majority of practical applications, very few investigations have been reported due to the complexity and high cost involved; (b) majority of these research works focused on the study of SCFs at certain positions such as the saddle, crown toe, and crown heel, and they have ignored the hot-spot stress (HSS) at other positions along the weld toe. In the present paper, effects of dimensionless geometrical parameters on the SCF distribution along the weld toe of main (outer) braces in the axially loaded right-angle two-planar tubular DKT-joints are investigated. In order to study the multi-planar effect, SCF distribution in two-planar joints is compared with the distribution in a uni-planar joint having the same geometrical properties. A complete set of SCF database is constructed based on the two-planar DKT-joint Finite element models which are verified against experimental results and the predictions of Lloyd’s Register (LR) equations. The FE models cover a wide range of geometrical parameters. Six new SCF parametric formulae are developed through nonlinear regression analyses for the accurate and reliable fatigue design of two-planar DKT-joints under axial loads. An assessment study of these equations is conducted against the experimental data, the original FEM database and the acceptance criteria recommended by the UK Department of Energy.     

大型核电厚壁结构X射线衍射法残余应力测试

采用X射线衍射法（ XRD）对大型核电厚壁结构堆芯板端面、堆芯板与吊篮筒体环焊缝焊前焊后残余应力进行无损测量。研究堆芯板端面、环焊缝焊前焊后残余应力的分布情况及变化规律。结果表明：堆芯板焊前残余应力主要是机加工应力,且焊接过程对其残余应力影响不大;1＃和2＃堆芯板环焊缝轴向残余应力分布趋势明显,呈现焊缝为压应力,母材为拉应力;测试的环向应力在各区域分布不一致;焊接对远离焊缝区域的应力没有影响,远离焊缝区域呈现较大的加工应力。     

Stress analysis of a transversely loaded aluminum weldment

The analysis of welded structural details is an important component in determining life cycle estimates. As part of a project to develop guidelines for reducing cracks in aluminum ship structures, the authors performed experiments showing that the stress levels developed strongly depend on the welded connection details. To properly quantify the effects of connection details, a stress analysis of the detail is required. This investigation summarizes the analysis of a common structural detail, one that results in a transversely loaded weldment.This paper is motivated by two sets of experimental test results. The first is the stress concentration observed at the intersection of the longitudinal and transverse members in a 1.5-m×3-m aluminum bottom panel tested under uniform pressure loading. The second is the reduction in fatigue life due to weld geometry variations between manually welded and machine-welded aluminum specimens. In order to clarify these two observations, the authors completed a detailed finite element analysis of a welded aluminum T-stiffener. The results show a significant stress concentration in the weld toe area. This stress concentration is shown to be strongly dependent on the weld toe geometry.