Internal residual stress measurement on linear friction welding of titanium alloy plates with contour method

The internal residual stress within a TC 17 titanium alloy joint welded by linear friction welding （LFW） was measured by the contour method, which is a relatively new and destructive technique to obtain a full map of internal residual stress. The specimen was first cut into two parts; the out-of-plane displacement contour formed by the release of the residual stress was then measured; finally, taking the measured contour of the cut plane as the boundary conditions, a linear elastic finite element analysis was carried out to calculate the corresponding distribution of residual stress normal to the cut plane. The internal stress distribution of the TC 17 titanium alloy LFWjoint was also analyzed. The results show that the tensile residual stress in the TC17 LFW weld is mainly present within a region about 12 mm from the weld centerline; the peak tensile residual stress occurs at the weld centerline and reaches 360 MPa （about one third of the yield strength of TC17 alloy）; within the weld zone of the TC17 LFW weld, the through-thickness stress is not uniform, and the internal stress is larger than that near the top or bottom surface.

A review of welding residual stress test methods

Due to local uneven heating during the welding process,the residual stress of the structure after welding affects the reliability of it.In order to ensure the reliability,it is of great significance to test the residual stress distribution of the welded joint.It has always been the focus to find a simple and feasible method for residual stress testing to quickly and accurately obtain the residual stress distribution of welded joints.The mechanical measurement method has high measurement accuracy,convenient and easy operation,but it will cause certain damage to the components.Physical measurement method can avoid damage to components,but its test cost is usually high,and its measurement accuracy can also be affected by the material microstructure characteristics of welded components.Based on the advantages and disadvantages of these two residual stress test methods,a modal test method is proposed.This method is a non-destructive measurement method.Based on the mathematical relationship between the residual stress of the welded structure and the natural frequency(mathematical model),the natural frequency is measured through the modal test to calculate the residual stress quickly.However,it is difficult to establish a mathematical model with this method,and it is not suitable for realization.

Mechanism of biaxial pre-stress method on welding residual stress and hot cracks controlling

Based on the conventional uniaxial pre-tensile stress method during welding, this study presents a new method of welding with biaxial pre-stress. With the help of numerical simulation, experiments were carried out on the self-designed device. Except for the control on residual stress and distortion us-welded, the experimental results also show its effect on the prevention of hot cracks, thus this method can make up for the disadvantage of the conventional pre-stress method. Hot cracks disappear when the value of pre-stress surpasses 0. 2 σs（yield limit）. Welded thin plates with low-level residual stress, little distortion and no hot cracks are obtained with longitudinal pre-tensile stress level between 0. 6σsand 0. 7σs and precompressive stress between 0. 2 σs and 0. 3 σs in transverse direction.

Use of Plastic Correction Formula to Improve Accuracy of Welding Residual Stress Test with Blind-Hole Method

The blind-hole method is the most widely used approach to experimentally determine the distribution of residual stress. This paper aims to improve test accuracy of welding residual stress and conducts an experimental study on the strain release factors involved when using the blind-hole method for Q235 and Q345, two steels commonly used in building structures. The ranges of strain release factors A and B in the elastic stage, the effects of strain release factors on residual stress calculated values, and the plastic corrected strain release factors are analyzed considering of the effect of plastic deformation around the blind hole on measurement accuracy. Finally, a simplified calculation formula to determine strain release factors is proposed for use with the blind-hole method. Results show that in the elastic stage, strain release factor A for Q235 and Q345 ranges from-0.399 to-0.525 and strain release factor B from-0.791 to-0.960. Changing the strain release factors A and B shows that calculated residual tensile stress varies in relation to a decrease in both factor values. However, there is a increase in calculated residual compressive stress with a decrease in the strain release factor A value, but there is an decrease with a decrease in strain release factor B value. Calculated residual stress applied to elastic strain release factors is compared with that applied to amended plastic strain release factors for Q235 steel. The maximum deviation between calculated residual stress and test stress is reduced from 21.1 to 1.0%,and for Q345 steel from 26.5 to 1.2%. It is thus evident that the plastic correction formula proposed in this paper can be used in calculations when conducting a residual stress test.

Prediction of Welding Residual Stress in 2.25Cr-1Mo Steel Pipe

A numerical analysis method was proposed to predict the welding residual stress in 2.25Cr-1Mo steel pipe considering solid-state phase transformations. A thermal elastic plastic finite element (FE) model considering effects of martensite transformation was developed based on commercial ABAQUS software. Continuous cooling transformation (CCT) diagrams were employed to simulate the fraction of martensite in fusion zone, coarse-grained heat affected zone and fine-grained heat affected zone. The Koistinen-Marburger relationship was used to trace the formation of martensite. The effects of both volume change and yield strength change due to phase transformation on welding residual stress were considered using the proposed FE model. The result shows that the phase transformation has significant effects on the welding residual stress in multi-pass butt weld of pipe. The predicted simulation results by the proposed numerical method are generally in good agreement with experimental results.

Distribution of Welding Residual Stress of Mixed Steel U-Rib-Stiffened Plates

To analyze the effects of width and thickness of each composition element of mixed steel U-rib-stiffened plates on the welding residual stress distribution, the distribution of the U-rib and the plate residual stress was calculated using a simplified calculation method. The method involved welding the mixed steel U-rib-stiffened plates for a structure with different sizes and different strength ratios of U-rib to plate. Based on a welding residual stress numerical simulation method validated by the blind hole method test, the distribution law of the mixed steel U-rib stiffened plate was studied. The results showed that the change of plate width has little impact on the welding residual stress and that the ratio of the thicknesses of the plate to U-rib stiffeners, the thickness of the plate, and the thickness of the U-rib has a great influence on the distribution of the welding residual stress. The thickness of plate and steel strength also greatly influenced the distribution width of the residual tensile stress. While analyzing the compression capacity of U-rib-stiffened plates, the simplified distribution of welding residual stress was used.

Residual stress and welding distortion of Al/steel butt joint by arc-assisted laser welding-brazing

The thermo-elastic.plastic finite element method(FEM)is used to simulate the thermo-mechanical behavior of Al/steel tungsten inert gas(TIG)arc-assisted laser welding-brazing(A-LWB)butt joint.The influence of material nonlinearity,geometrical nonlinearity and work hardening on the welding process is studied,and the differences in the welding temperature field,residual stress and welding distortion by A-LWB and by single laser welding-brazing(SLWB)are analyzed.The results show that the thermal cycle,residual stress distribution and welding distortion by the numerical simulation are in good agreement with the measured data by experiments,which verifies the effectiveness of FEM.Compared with the SLWB,A-LWB can make the high-temperature distribution zone of weld in width direction wider,decrease the transverse tensile stress in the weld and reduce the distribution range of longitudinal tensile stress.And the welding deformation also decreases to some extent.

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates（50 mm thick） by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.

Three-Dimensional Thermo-Elastic-Plastic Finite Element Method Modeling for Predicting Weld-Induced Residual Stresses and Distortions in Steel Stiffened-Plate Structures

The objective of the present paper is to develop nonlinear finite element method models for predicting the weld-induced initial deflection and residual stress of plating in steel stiffened-plate structures. For this purpose, three-dimensional thermo-elastic-plastic finite element method computations are performed with varying plate thickness and weld bead length (leg length) in welded plate panels, the latter being associated with weld heat input. The finite element models are verified by a comparison with experimental database which was obtained by the authors in separate studies with full scale measurements. It is concluded that the nonlinear finite element method models developed in the present paper are very accurate in terms of predicting the weld-induced initial imperfections of steel stiffened plate structures. Details of the numerical computations together with test database are documented.

3D Finite Element Numerical Simulation of Residual Stresses on Electron Beam Welded BT20 Plates

A three-dimensional finite-element model (FEM) used for calculating electron beam (EB) welding temperature and stresses fields of thin plates of BT20 titanium has been developed in which the nonlinear thermophysical and thermo-mechanical properties of the material has been considered. The welding temperature field, the distributions of residual stresses in as-welded (AW) and electron beam local post-weld heat treatment (EBLPWHT) conditions have been successfully simulated. The results show that: (1) In the weld center, the maximum magnitude of residual tensile stresses of BT20 thin plates of Ti alloy is equal to 60%- 70% of its yield strength σs. (2) The residual tensile stresses in weld center can be even decreased after EBLPWHT and the longitudinal tensile stresses are decreased about 50% compared to joints in AW conditions. (3) The numerical calculating results of residual stresses by using FEM are basically in agreement with the experimental results. Combined with numerical calculating results, the effects of electron beam welding and EBLPWHT on the distribution of welding residual stresses in thin plates of BT20 have been analyzed in detail.

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.

Research on welding simulation methods and software development

To develop highly efficient and useful software, we need to understand the essential feature of the welding phenomenon. From the mechanical point view, welding is a transient nonlinear problem in which small but strongly nonlinear region is moving with the welding torch. Noting this characteristic, ISM （Iterative Substructure Method） was developed for the thermal-elastic-plastic analysis of large scale structures. It is also known that the welding distortion and the residual stress are produced by inherent strain. The inherent strain is the sum of irreversible strains such as plastic strain due to welding thermal cycles or phase transformation and creep strain. In addition to the inherent strain, the mismatch produced by cutting error and fitting is also an important cause of the welding distortions and residual stresses. Based on this understanding, an elastic FEM introducing the inherent strain and mismatch is developed. The potential capabilities of these methods are demonstrated through some examples.

Determination of Residual Stresses Numerically Obtained in ASTM AH36 Steel Welded by TIG Process

Residual stresses have been numerically determined in welded joints. In this study, the numerical model is based on the coupling of different physical phenomena considering the thermal, mechanical and metallurgical nature of a welding process. The ABAQUS software program was used to perform the numerical simulations, based on the finite element method (FEM). The aspects related to the mathematical modeling of complex welding procedures were pondered with the FEM: variations in the physical and mechanical properties of the materials as a function of the temperature;the transience and the speed of the welding process, the material phase transformations;the different mechanisms of heat exchange with the environment (convection and radiation);all them associated with a high level of nonlinearity. The heat source used in this analytical model for heat supply was the double ellipsoid model proposed by Goldak, in which a 60 mm × 50 mm and 3 mm rectangular ASTM AH36 steel plate was used for the TIG process simulations. Throughout this work, the optimization of the welding procedures currently practiced in petrochemical and ship building industries can be applied to reduce the levels of residual stresses.

Q690厚板对接焊残余应力评估及其对焊接接头断裂性能的影响

[目的]旨在研究高强钢厚板多层多道焊的复杂焊接残余应力,评估其对焊接接头断裂性能的影响。[方法]以75 mm厚Q690高强钢板为研究对象,制定多层多道对接焊工艺,完成对接接头的焊接,使用轮廓法获得中剖面的纵向残余应力,基于自主开发的高效热−弹−塑性有限元计算方法,再现厚板多层多道焊的热循环、微观组织演变等现象,将单轴拉伸试验与GTN损伤模型相结合,提出Q690高强钢板的GTN模型参数,分析金属母材及焊接接头试样的断裂特性和应力−应变曲线。[结果]采用所提方法预测的厚板对接接头熔池形状、金相体积分数都与试验测量基本吻合;考虑焊接固态相变和高强钢轧制初始应力的力学分析,得到的焊接残余应力与试验结果高度一致,并得到了横向残余应力分布;考虑焊接微观缺陷及横向残余应力,阐明了残余应力影响焊接接头断裂性能的力学机理。[结论]相关研究可为高强钢厚板焊接结构残余应力及断裂性能评估提供借鉴和指导。

能量配比对6 mm 7A52铝合金板材VPPA-MIG复合焊接残余应力分布的影响

VPPA-MIG复合焊接的热源由VPPA和MIG两种电弧热源混合而成,该焊接方法集合了MIG焊接效率高、参数区间宽以及VPPA焊接能量集中、穿透深度大等优点,能够实现不同厚度铝合金板材的高效率和高质量焊接。在铝合金板材VPPA-MIG复合焊接过程中,VPPA与MIG两种电弧不同能量配比会影响焊后接头的残余应力分布。以6 mm厚7A52铝合金板材为试验材料,设置VPPA电弧能量配比不同的焊接参数进行VPPA-MIG复合焊接试验,焊后采用钻孔法测试并分析了接头残余应力分布及峰值大小。结果表明,复合焊接接头的熔合区和热影响区出现拉应力,母材区出现压应力。在复合焊接热源总能量不变的情况下,残余应力峰值随VPPA电弧能量配比的增加而增大,且当VPPA电弧能量配比从35%增大至40%时,可以获得成形效果良好的复合焊缝,横向残余应力峰值不超过73 MPa,纵向残余应力峰值不超过232 MPa,不会出现过大的残余应力峰值。与单MIG焊接相比,VPPA-MIG复合焊的残余应力峰值比单MIG焊大,而高应力区要比单MIG焊窄。

考虑残余应力影响的桥式起重机多轴疲劳寿命评估

桥式起重机桥架结构是典型的焊接结构,在日常服役时主梁焊缝区域经常出现疲劳裂纹。为保证起重机的服役安全,基于多尺度有限元分析方法建立危险裂纹区域的多级子模型;在二级子模型上建立热-结构耦合焊接有限元模型并模拟分析了焊接的全过程,通过模拟焊后热处理分析对残余应力的影响;结合多轴临界面法构建了以应变幅值作为多轴损伤参量的疲劳分析方法,评估了危险裂纹区域的疲劳性能。结果表明:所提方法将结构整体疲劳问题转化成局部焊接位置的疲劳问题,不仅增加了计算效率,还能考虑疲劳细节处更多的影响因素,为起重机焊缝部位的疲劳寿命评估和延寿提供了一定的参考。

不同方法消除焊接残余应力效果比较分析

焊接残余应力不仅影响离心泵承压件的强度,其产生的变形也不利于安装精度的控制,进而影响离心泵的稳定性。因此,研究不同方法消除焊接残余应力的效果,选出适用于离心泵承压件的焊接残余应力消除方法对离心泵稳定运行有重要作用。通过对泵盖承压件不同方法消应力前后的残余应力测量得出,整体热处理的方式能够消除73%的残余应力,效果最明显;局部热处理能够消除44.8%的残余应力;振动时效未达到消应力效果。

考虑残余应力的钢桥面板-肋双面焊裂纹应力强度因子计算方法

建立焊接分析有限元模型,对顶板-纵肋双面焊构造的焊接过程进行数值模拟,拟合得到顶板焊趾细节沿板厚方向分布的横向残余应力分布经验公式;建立钢桥面板断裂力学数值模型,结合统一的权函数表达式,推导适用于顶板焊趾处裂纹最深点和表面点应力强度因子的新权函数,并将权函数计算的应力强度因子与有限元计算的应力强度因子进行对比。研究结果表明:顶板-纵肋双面焊顶板焊趾处残余应力沿板厚方向处于拉—压—拉状态,呈正弦函数分布;在二次应力分布下,权函数法与有限元法计算所得顶板焊趾处裂纹最深点应力强度因子最大相对误差为7.4%,表面点应力强度因子最大相对误差为4.1%;在焊接残余应力场下,权函数法与有限元法计算所得顶板焊趾处裂纹最深点应力强度因子最大相对误差为7.6%,表面点应力强度因子最大相对误差为8.6%;权函数法能有效计算钢桥面板-肋双面焊顶板焊趾处疲劳裂纹应力强度因子。

基于应变场强法的钢桥面板顶板-纵肋焊接节点疲劳寿命预测

钢桥面板顶板-纵肋焊接节点处疲劳现象频发,应力集中和残余应力是影响其疲劳寿命的关键因素。然而,常用评估方法大多以距焊趾/根一定距离的某一点的应力状态作为参量,忽略了焊接节点附近区域应力分布对疲劳寿命的影响。场强法可通过权函数考虑焊接节点附近区域的应力分布,因此本工作采用场强法进行顶板-纵肋焊接节点的疲劳寿命预测。基于已有疲劳试验,采用ANSYS软件建立顶板-纵肋焊接节点的有限元模型;再利用热-结构顺序耦合法计算残余应力,并施加疲劳荷载,得到应力幅最大位置的应变场强;最后,对适用于低周疲劳寿命评估的Manson-Coffin公式进行修正,实现该节点的高周疲劳寿命预测。研究结果表明:考虑残余应力计算的疲劳寿命较不考虑时误差会减小21.2%;与名义应力法、能量法相比,采用应变场强法预测的疲劳寿命精度会分别提高31.5%、38.2%。

基于热弹塑性有限元法的双腹加筋板焊接顺序研究

为进一步研究双腹加筋板不同焊接顺序下残余应力和变形的分布规律,基于热弹塑性有限元法,采用有限元软件Abaqus对双腹加筋板进行了焊接数值模拟,分析了双腹加筋板不同焊接顺序下残余应力和变形的分布规律。分别采用壳单元和实体单元对双腹加筋板远离焊缝区及焊缝区建模,以提高计算效率,并建立了壳单元与实体单元自由度之间的线性约束。计算比较了双腹板同步焊接与连续焊接下的加筋板焊接残余应力与变形,共计17种焊接顺序。结果表明:相比于连续焊接,双腹加筋板采用同步焊接产生的残余应力与角变形较小,双腹加筋板同步焊接角变形的幅值比连续焊接角变形幅值减小了47.1%。