外部约束对薄壁高温合金尾喷管焊接变形的影响

以壁厚为1 mm的高温合金尾喷管为研究对象，基于热-弹-塑性有限元法与固有应变法，研究外部约束对薄壁高温合金尾喷管工件焊接变形的影响。通过焊接工艺试验和热-弹-塑性有限元法仿真，进行焊接热源校核，获得对接接头的固有应变和材料模型参数。建立全尺寸三维尾喷管焊接有限元模型，基于固有应变理论的弹性有限元方法，利用平板对接获得的材料模型参数，计算不同外部约束对尾喷管工件焊接变形的影响。结果表明：进气口约束对控制尾喷管焊后变形起主要作用，在进气口施加约束时，工件变形最小，为2.39 mm,变形发生在尾喷管内环与外环弧形焊缝位置。通过尾喷管组件产品焊后变形测量与仿真结果对照，验证了仿真计算方法的准确性，固有应变法可适用于薄壁尾喷管焊接变形预测。     

薄壁GH3536尾喷管组焊变形控制工艺优化仿真

基于SYSWELD仿真平台,利用热-弹-塑性有限元法和固有应变法进行仿真优化,研究焊接工艺对薄壁GH3536尾喷管组件焊接变形的影响。首先进行平板对接工艺试验和热-弹-塑性有限元仿真计算,对焊接热源模型进行校核,获得不同焊接工艺下典型接头的平均固有应变和修正的材料热膨胀系数。建立全尺寸三维尾喷管组件的焊接有限元模型,基于固有应变理论的弹性有限元方法,利用平板对接获得的材料热膨胀系数,计算焊接工艺参数与焊接约束对尾喷管组件焊接变形的影响。结果表明,焊接电流为40A时,薄壁GH3536平板对接焊接头固有应变值最小为0.00660mm,此时尾喷管焊后变形也最小,为推荐使用的最优焊接工艺。在焊缝、进气口和排气口同时进行夹持,尾喷管焊后变形最小,整体变形1.39mm。     

铝合金薄板固有变形逆解析方法的研究与开发

为了获得可靠的铝合金焊接接头上固有变形,开发一种将实验与基于固有应变的有限元法(FEM)融为一体的新方法来获得接头的固有变形。为了澄清铝合金薄板焊接固有变形的分布特征,先采用热-弹-塑性有限元计算铝合金TIG重熔接头的焊接变形,并建立固有变形在接头上的简化分布模型。其次,以该模型为基础,提出一种通过测量焊接接头上少数位置上焊前和焊后三维坐标来逆向求解固有变形的计算方法。最后,将利用该算法获得的铝合金薄板接头固有变形代入到基于固有应变理论的弹性有限元分析中,计算得到的焊接变形能较好地再现热-弹-塑性有限元方法计算得到的结果和实验结果。结果表明:采用提出的逆解析方法来获得铝合金接头的固有变形是有效可行的。     

薄板焊接失稳变形的简化模型及其应用

提出了基于固有应变对接薄板失稳分析的基本方程.通过将固有应变等效为焊缝及热影响区的热载荷,可以进行线性失稳分析确定临界载荷,然后采用非线性失稳分析确定失稳变形的大小.对不同焊接工艺条件下的低碳钢薄板对接焊变形进行了研究,比较了数值分析与试验测量结果,并且数值计算考虑了薄板不平整度的影响.最后,使用该简化的方法对有加强筋板分段结构的焊接变形进行预测.研究表明,基于固有应变等效载荷的失稳变形计算方法是简单、有效的.     

固有应变法在T型接头焊接变形研究中的应用

本文以固有应变理论为基础,介绍了两种固有应变模拟焊接变形的计算和加载方法,并通过对T型接头焊接变形的分析实例讨论了两种模拟方法的差异,并与相同实体模型热弹塑分析的变形结果进行比较,验证了固有应变法计算焊接变形的合理性与准确性,为预测大型焊接结构变形提供了参考方法。     

焊接顺序对大型薄板装甲钢结构焊接变形的影响

基于有限元软件SYSWELD建立了大型薄板装甲钢结构的焊接有限元模型,采用Local-Global方法研究了焊接顺序对薄板结构焊接变形的影响. 通过对比焊缝截面宏观形貌,利用SYSWELD热源拟合工具,建立了适合现场焊接工艺的双椭球热源模型. 采用热弹塑性有限元法分析了T形和对接接头的焊接过程,获得了局部塑性应变和焊缝刚度,进而模拟了不同焊接顺序下薄板结构变形情况. 结果表明,现场焊接顺序下结构中部薄板焊接变形严重,最大变形量为9.6 mm,模拟结果与试验结果吻合较好;采用优化的焊接顺序,可有效控制薄板焊接变形,最大变形量可减小75%.     

大型船体舷侧分段装焊顺序仿真及其变形预测研究

针对大型船体结构焊接仿真及变形预测困难等问题,综合运用热弹塑性有限元法和固有应变法实现船体舷侧分段装焊工艺仿真,重点研究不同装焊顺序对焊接变形的影响。系统分析了船体舷侧分段的焊缝类型及其焊接工艺;基于热弹塑性有限元法获取典型焊缝接头的固有应变;进而采用固有应变法分析了不同装焊顺序下舷侧分段的焊接变形及其分布规律。结果表明:舷侧分段呈现纵向两端向中间收缩变形趋势,最大变形量发生在内外板衔接处。反造法相对于正造法的装焊工艺,焊后变形在x、y方向的最大变形量分别提高0.8%、5%,在z方向的最大变形量降低4.4%为提高大型船体结构装焊效率和质量提供了理论支撑。     

高强度钢T型接头焊接变形固有应变数值模拟

以固有应变理论为基础,介绍了两种固有应变模拟焊接变形的计算和加载方法;以高强度钢T型接头焊接变形为算例,讨论了两种模拟方法的差异;通过与相同实体模型热弹塑性变形结果的分析比较,验证了固有应变法预测焊接变形的合理性与准确性,为更合理的利用固有应变法预测大型焊接结构残余变形提供了有益的参考.     

固有应变有限元法预测焊接变形理论及其应用

介绍了固有应变的概念、固有应变有限元法预测焊接变形的理论和方法。固有应变存在于焊缝与近缝区 ,并与焊接热输入和板厚等因素有关 ,通过试验和热弹塑性分析 ,可以确定它们的关系曲线。固有应变法只需一次弹性有限元计算 ,因而是预测大型复杂结构焊接变形的一种十分有效的方法。文中介绍了若干工程中成功的应用实例     

试件尺寸对Q345薄板单道堆焊接头变形的影响

基于ABAQUS有限元分析软件,开发了考虑移动热源、材料非线性和几何非线性的热-弹-塑性有限元计算方法,用于模拟薄板焊接接头的温度场和焊接变形. 利用所开发的方法数值研究了试件尺寸对板厚为2 mm Q345低合金高强钢单道堆焊接头焊接变形的影响. 同时,采用试验方法测量了薄板接头的面外变形. 通过数值模拟结果与实测值的比较,验证了所开发的非线性有限元方法的有效性. 结果表明,试件尺寸对Q345薄板接头的变形量和变形分布都有显著影响. 此外,还详细讨论了在不同长宽比条件下薄板面外变形的产生机理.     

冷热冲击对无铅钎料可靠性的影响

文中对比了一种新型低银钎料Sn-Ag-Cu-Bi-Ni（SACBN07）与市场上的SAC305,SAC0307两种无铅钎料的抗冷热冲击性能.利用纳米压痕试验等微观测试方法研究时效后界面组织及力学性能的变化.结果表明,SACBN07的抗冷热冲击性能最好,焊点失效后三种材料中裂纹的扩展路径不同,SAC305失效裂纹位于体钎料中,SACBN07钎料断裂位置逐渐由钎料基体转移到金属间化合物（IMC）层中,而SAC0307断裂位于界面IMC中;钎料中Bi,Ni元素的加入有效地抑制了IMC的生长,相同冷热冲击时间,SACBN07钎料中界面IMC厚度最薄;SACBN07体钎料的硬度受冷热冲击影响最小,时效后仅降低了8.6%,而SAC305与SAC0307分别降低了12.5%和28.3%.     

薄板搭接接头固有变形逆解析方法

文中采用变形测试和数值模拟技术相结合的研究手段对低碳钢薄板搭接接头固有变形的求解方法进行了研究,提出了该接头的固有变形分布简化模型,并利用固有变形逆解析方法推定了3 mm低碳钢薄板的固有变形.使用该方法得到的固有变形值来预测焊接变形能较好的再现试验结果.结果表明,采用文中提出的固有变形分布简化模型能获得高精度的固有变形值,搭接接头固有变形的逆解析算法是正确有效的.     

Efficient Simulation of Welding Distortion in Large Structures and Its Reduction by Jig Constraints

Two large construction machinery structures were welded separately with and without jig constraints. The welding distortion of the entire structure was measured by a 3D coordinate measuring system and simulated by elastic FEM using the inherent deformation method. To obtain an accurate inherent deformation, a thermal elastoplastic FE analysis of simple one-side fillet joints with and without jig constraints was performed. Efficient simulation of welding distortion in large structures was accomplished by applying inherent deformation in a localized region, and the effect of jig constraint on the reduction of welding distortion was clarified. The computation of inherent deformation, the weld zone definition and the conversion of inherent deformation into inherent strain were automated. Measured and computed welding distortions in large structures had a good correspondence with respect to both tendency and magnitude. Further investigation of jig configuration was performed for enhanced reduction of welding distortion. Alternative controlling techniques for common welded structures were also addressed.     

A mechanism of formation of a single section of a vacuum discontinuous coating

A welding distortion prediction method based on the inherent strain concept is presented. In the proposed method, welding distortion of large-welded structures could be estimated by elastic analysis using the result of thermal-elastic–plastic analysis and the result of smaller welded joints or components. Thermal-elastic–plastic analysis is performed to calculate residual plastic strain distribution, which is the input data for the elastic analysis of welding distortion. The obtained residual plastic strain distribution is mapped to non-deformed finite element models to calculate welding distortion by elastic analysis. The mapping procedure is done in different ways for welding start/end parts and the rest of the weld length in order to take into consideration the unsteady strain distribution at the start/end of welds. For start/end parts, strain distribution used is identical with thermal-elastic–plastic analysis. For the part except start/end parts, strain distribution obtained by thermal-elastic–plastic analysis is extracted from the centre of weld length and is extruded along the welding direction.

The proposed method was applied to the welding distortion prediction of joints with weld length of 900 and 1200 mm based on the thermal-elastic–plastic analysis result of a joint with weld length 600 mm. The estimated results were in good agreement with the thermal-elastic–plastic analysis results of models of corresponding weld length to show the validity of the proposed method.     

斜十字接头三维焊接残余应力的数值模拟

为研究全熔透焊接十字接头残余应力空间分布特点,分析十字接头焊缝形式对焊接残余应力分布状态的影响,基于温度场和应力场间接耦合方式,对全熔透焊接十字接头残余应力开展了有限元数值模拟研究. 采用ANSYS有限元软件,选择Q345C钢材典型热力学参数,构建全熔透焊接十字接头有限元模型,分析得到焊接过程结构温度场分布. 将焊接十字接头温度场作为输入条件,基于ANSYS热–力耦合分析得到全熔透焊接斜十字接头三维残余应力场分布. 结果表明,全熔透焊接十字接头残余应力峰值主要分布在焊趾和焊根处,焊缝角度变化会对焊缝处残余应力分布带来较大影响.     

Welding deformation produced by two-pass welding

Multilayer welding is considered to be an accumulation of two-pass welding, and it was clarified that the basic factors of welding deformation were produced by two-pass welding. From comparison between the experimental results and numerical analysis, it was found that the numerical analysis method used in this research was very accurate to predict the welding deformation. Also, the influences of the welding heat input and the distance between two-passes on the welding deformation were examined by using the numerical analyses. As a result, it was found that the longitudinal shrinkage made from each pass was decided by the inherent strain distribution parallel to the weld line. The inherent strain distribution parallel to the weld line after two-pass welding was a larger value at one- or two-pass welding. On the other hand, it was revealed that transverse shrinkage made from each pass was decided by the integration of inherent strain distribution perpendicular to the weld line. In the case of the inherent strain distribution perpendicular to the weld line after two-pass welding, it was clarified that the inherent strain was almost same as the sum of inherent strain distribution perpendicular to the weld line made from each pass.     

Experimental and computational analysis of residual buckling distortion of bead-on-plate welded joint

A test specimen with a thickness of 2.28 mm was selected as the examined object, to investigate welding induced buckling. Bead-on-plate welding was conducted on the test specimen and residual buckling distortion was observed. A thermal-elastic-plastic (TEP) FE analysis using solid elements model was carried out to predict welding induced buckling after cooling. The inherent deformation of the examined welded joint was also evaluated from the computed results of TEP FE analysis. A shell elements model of the test specimen was used for eigenvalue and elastic FE analyses based on the inherent deformation theory. Eigenvalue analysis predicted the buckling mode and corresponding tendon force in the examined welded joint. Considering large deformation and initial deflection, an elastic FE analysis was carried out to predict the out-of-plane welding distortion, which showed a good agreement with measured distortion.The generation mechanism of buckling in bead-on-plate welded joint was clarified employing the inherent deformation theory. The tendon force (longitudinal inherent shrinkage) is the dominant reason to produce buckling and the disturbance (initial deflection or inherent bending) triggers buckling but does not influence the buckling mode.     

Influences of external restraint on welding distortion in low carbon steel bead-on thin plate joints

The out-of-plane deformation is a serious problem in thin-plate welded joint, and it is difficult to reduce or control the distortion during welding process.External restraint is regarded as an effective method to mitigate the distortion, and it is widely used in the actual manufacturing process.In order to investigate the influence of external restraint on welding deformation in thin plate joints, a thermo-elastic-plastic finite element method based on ABAQUS software was developed to calculate welding-induced deformation.Meanwhile, welding deformation in the thin-plate joints was measured by experiments.Through comparing the numerical results with the measured data, the effectiveness of the developed computational approach was verified.Based on the simulated and experimental results, the generation mechanism of the out-of-plane deformation in thin plate bead-on joint was discussed, and the influence of external restraint on the final welding deformation was clarified.     

Deformation analysis of a friction stir-welded thin sheet aluminum alloy joint

The deformation characteristics of a friction stir welded thin sheet aluminum alloy joint were analyzed via numerical simulations.The simulated results were compared with the experimental results obtained for the deformation of actual welded joints.The results revealed that the deformation of the joint was described by an asymmetric distribution with a large deformation region occurring mainly in the advancing side.This asymmetric deformation was mainly caused by the direct mechanical force applied by the welding tool to the workpiece.Furthermore,the deformation characteristics of the fixed points on both sides of the weld revealed that the deformation of the retreating side fluctuated significantly during the welding process.That is,the retreating side exhibited less welding stability than the advancing side.The stress distribution of the welded joint showed that a high stress region was formed at the end of the weld.In addition,the final stress distribution of the welded joint resulted mainly from the shear stress in the x-y direction.     

Comparative study on evaluation of tendon force for welding distortion prediction in thin plate fabrication*

Tendon force is an essential concept to predict welding distortion such as longitudinal shrinkage and welding induced buckling in thin plate fabrication.In this study,three approaches with experimental,theoretical and computational analysis,are examined to evaluate the magnitude of tendon force.In detail,inherent deformation theory is introduced first,the theoretical analysis to obtain the inherent strain solution is also reviewed;and then analytical solution for tendon force is achieved.Also,the theory of FE analysis for welding is introduced and implemented in a computation to obtain the transient temperature distribution,plastic strain,residual stress and welding distortion in a bead-on-plate welded joint with 2.28 mm in thickness.The longitudinal displacement is employed to evaluate tendon force directly,and these computed inherent strain and inherent stress can also be employed to evaluate tendon force by integration approach later.All the evaluated magnitudes of tendon force have a good agreement with each other.