Effect of heat source configuration on the result quality of numerical calculation of welding-induced distortion

The results of numerical welding simulations strongly depend on its temperature field. In the present paper, the temperature field of a pulsed gas metal arc weld of structural steel S355J2+N (ASTM A572 Gr. 50) with a thickness of 5 mm is experimentally and numerically investigated. In the case of temperature field validation, volumetric Gauss and double-ellipsoid Goldak heat sources are applied. Additionally, different heat source configurations, including adaptations of thermal conductivity, are analyzed regarding their influence on the calculation of welding-induced distortion.The investigations clarify the influence of heat source configurations on the calculated results, thus, contribute to an improved prediction of welding-induced distortion.     

Prediction of angular distortion in the fiber laser keyhole welding process based on a variable-fidelity approximation modeling approach

The angular distortion is one of the most common types of distortions frequently observed in laser weld assembling processes, which leads to a decline in welding joints’ quality and additional costs of rework. Therefore, it is of great importance to control and reduce the welding-induced angular distortion by selecting appropriate welding process parameters. The challenge is how to predict the welding-induced angular distortion in the whole process parameter design domain accurately and efficiently. To address this challenge, a variable-fidelity approximation modeling approach is developed in this paper, where two different levels of fidelity data are integrated for predicting the angular distortion in the laser welding process. In the proposed approach, a three-dimensional thermo-mechanical finite element model is developed as a low-fidelity model, while the laser welding experiment is taken as a high-fidelity model. A low-fidelity radial basis function (RBF) model is constructed based on the sample data from the finite element simulation. Then a linear tuning strategy is introduced to bring the low-fidelity RBF model as close as possible to the data from the laser welding experiment. Finally, the variable-fidelity approximation model is constructed by adopting a scaling function to calibrate the remaining differences between the tuning low-fidelity approximation model and the high-fidelity data. Two types of validation approaches are adopted to compare the prediction accuracy of the variable-fidelity approximation model with those of the single-fidelity approximation models solely constructed with laser welding experiment or finite element simulation. Results illustrate that the prediction ability of the developed variable-fidelity approximation model outperforms those of the single-fidelity approximation models.     

Numerical simulation of the electron beam welding process

Electron beam welding is a highly efficient and precise welding method that is being increasingly used in industrial manufacturing and is of growing importance in industry. Compared to other welding processes it offers the advantage of very low heat input to the weld, resulting in low distortion in components. Modeling and simulation of the laser beam welding process has proven to be highly efficient for research, design development and production engineering. In comparison with experimental studies, a modeling study can give detailed information concerning the characteristics of weld pool and their relationship with the welding process parameters (welding speed, electron beam power, workpiece thickness, etc.) and can be used to reduce the costs of experiments. A simulation of the electron beam welding process enables estimation of weld pool geometry, transient temperature, stresses, residual stresses and distortion. However this simulation is not an easy task since it involves the interaction of thermal, mechanical and metallurgical phenomena. Understanding the heat process of welding is important for the analysis of welding structure, mechanics, microstructure and controlling weld quality.In this paper the results of numerical simulation of electron beam welding of tubes were presented. The tubes were made of 30HGSA steel. The numerical calculation takes into consideration thermomechanical coupling (TMC). The simulation aims at: analysis of the thermal field, which is generated in welding process, determination of the heat-affected zone and residual stresses in the joint. The obtained results allow for determination both the material properties, and stress and strain state in the joint. Furthermore, numerical simulation allows for optimization of the process parameters (welding speed, power of the heat source) and shape of the joint before welding. The numerical simulation of electron beam welding process was carried out with the ADINA System v. 8.6. using finite element method.     

Multi-objective optimal design of small scale resistance spot welding process with principal component analysis and response surface methodology

This paper investigates the effects of welding parameters on the welding quality and optimizes them in the small scale resistance spot welding (SSRSW) process. Experiments are carried out on the basis of response surface methodology technique with different levels of welding parameters of spot welded titanium alloy sheets. Multiple quality characteristics, namely signal-to-noise (S/N) ratios of weld nugget diameter, penetration rate, tensile shear load and the failure energy, are converted into an independent quality index using principal component analysis. The mathematical model correlating process parameters and their interactions with the welding quality is established and discussed. And then this model is used to select the optimum process parameters to obtain the desired welding quality. The verification test results demonstrate that the method presented in this paper to optimize the welding parameters and enhance the welding performance is effective and feasible in the SSRSW process.     

一种基于神经网络的畸变图像校正方法

由于摄像机获取的图像存在几何畸变，因此在对图像进行定量分析前，必须校正畸变。针对传统的畸变图像校正方法，其所建立的畸变数学模型，不仅求解畸变参数复杂、计算量大，且存在很大的数值计算误差的问题．提出了一种基于神经网络的畸变图像校正方法。该方法首先运用图像处理技术从一标准模板的畸变图像中提取样本，然后以样本像素坐标作为网络输入来对神经网络进行训练。由于该训练好的神经网络能够实现畸变图像与非畸变图像之间的映射关系，因此能达到校正图像畸变的目的。最后对该校正方法进行了实验，给出并分析了校正实验结果，校正效果令人满意，并已成功地用于焊接机器人视觉系统。     

Influence of groove type on welding-induced residual stress,deformation and width of sensitization region in a SUS304 steel butt welded joint

To join a medium or thick plate weldment with a full penetration, a groove is usually prepared in the space between two sections of metal. Because weld metal needs to be deposited within the groove to form the joint, it is expected that different groove type will require different heat input, which may consequently have influence on welding residual stress and deformation. Generally, different groove corresponds to different bead layout, so it can be foreseen that the groove type has a significant effect on temperature history, shape and size of heat affected zone, and region of sensitization in certain alloys such as austenitic stainless steel. The influences of groove type on residual stress, angular distortion and width of sensitization region in a SUS304 butt-welded joint were investigated by means of numerical simulation and experiment. Based on ABAQUS code, a computational approach with considering thermo-mechanical coupling behaviors, moving heat source, strain hardening and annealing effect was developed to simulate temperature profile, stress field and deformation in multi-pass joint. Welding temperature cycles, residual stress distributions and deformations in V, K and X groove joints were calculated through using the proposed computational procedure. Meanwhile, experiments were carried out to obtain residual stress distributions and angular distortions. Through comparing the numerical results and the measured data, the effectiveness and accuracy of the developed computational approach were verified. The simulation results show that groove type has a significant influence on welding residual stress distribution, angular distortion and width of sensitization region.     

Ⅱ-VI族半导体的掺杂与补偿

采用离散变分局域密度泛函（ＤＶＬＤＦ）方法及团簇模型研究了ＩＩＶＩ族半导体中的掺杂及补偿问题。研究了ＺｎＳｅ中的Ｎ，Ｐ，Ａｓ，Ｆ，Ｃｌ，Ｂｒ等杂质不同的结构和电子性质。发现ＮＳｅ在ＺｎＳｅ中没有ＪａｈｎＴｅｌｅｒ形变，而ＰＳｅ和ＡｓＳｅ存在这一形变，从而判定Ｎ是其中最有效的ｐ型掺杂剂。对于ｎ型的ＺｎＳｅ，研究发现Ｃｌ是最有效的施主杂质。根据对缺陷复合体的计算，发现ＮＳｅＺｎＶＳｅ及诸如ＮＳｅＺｎｉｎｔ的多Ｎ集团对于ｐ型ＺｎＳｅ的补偿有着重要作用。研究表明，对于ＺｎＴｅ来说，Ｃｌ不是有效的施主杂质，而Ｎ是有效的受主杂质。     

基于加权巴克谱失真的语音质量客观评价算法

提出了一种基于加权巴克谱失真（WBSD）的语音质量客观评价算法。鉴于不同巴克带谱失真对语音质量的影响程度不同,该算法提出在巴克域中对不同巴克带谱失真进行加权来求失真语音的客观失真测度。并且通过分析改进型巴克谱失真测度（MBSD）中15个巴克带失真与平均意见分（MOS）间的相关度,提出了一组以相关系数幂次方为权重的有效巴克谱失真权重矢量。实验结果表明：与MBSD算法相比,WBSD在算法复杂度没有明显增加的情况下与MOS的相关度提高了3％。     

Evaluation of electron beam welding technique for the integration of robust sensor elements into high-pressure automotive systems

For “on board” diagnosis purposes of the injected fuel quantity flow sensitive elements based on the thermo-resistive measurement principle were integrated into finished Common Rail injection nozzles of valve-covered orifice (VCO) or mini-sac hole (MSH) class. Electron-discharge machining as well as electron beam welding technique are key technologies for a reliable integration procedure. To demonstrate negligible influence on the hydraulic performance of the nozzle after modification an optical measurement set-up is used to record temporally resolved the propagation of the spray patterns ejected from the six injection holes simultaneously. From these investigations the impact on the structural distortion of the valve caused by the welding seam is proved as its position can be directly linked to any chances in spray performance of each individual injection hole. Reducing the energy input during the electron beam welding lowers substantially the asymmetry in spray patterns from hole to hole as the needle uncovers the six injection holes more symmetrically. Besides this important finding, the numerical calculations indicate that the implementation of the sensor chip slightly amplifies the asymmetry induced by the welding process due to an additional weakening of the nozzle body which is confirmed experimentally. Despite these challenges, however, it is demonstrated that appropriate parameters for the integration procedure can be found affecting the hydraulic performance negligible compared to the original state.     

Numerical comparison of nonlinear programming algorithms for structural optimization

For FE-based structural optimization systems, a large variety of different numerical algorithms is available, e.g. sequential linear programming, sequential quadratic programming, convex approximation, generalized reduced gradient, multiplier, penalty or optimality criteria methods, and combinations of these approaches. The purpose of the paper is to present the numerical results of a comparative study of eleven mathematical programming codes which represent typical realizations of the mathematical methods mentioned. They are implemented in the structural optimization system MBB-LAGRANGE, which proceeds from a typical finite element analysis. The comparative results are obtained from a collection of 79 test problems. The majority of them are academic test cases, the others possess some practicalreal life background. Optimization is performed with respect to sizing of trusses and beams, wall thicknesses, etc., subject to stress, displacement, and many other constraints. Numerical comparison is based on reliability and efficiency measured by calculation time and number of analyses needed to reach a certain accuracy level.The research project was sponsored by the Deutsche Forschungsgemeinschaft under research contract DFG-Schi 173/6-1     

Mesh, gravity and load effects on finite element simulations of blast loaded reinforced concrete structures

The behavior and design of reinforced concrete blast resistant structures are supported by intensive numerical simulations, and the effects of various parameters on the results is of great interest. Finite element simulations were performed in the nonlinear dynamic domain with modified concrete and steel constitutive models. Ten different cases were implemented, each with different reinforcement details. In addition, each case included both a coarse mesh and a fine mesh to determine the effects of mesh resolution on the numerical simulations. Gravity and loading conditions were altered to investigate their influences on the results. Deformations and stress distributions in both the concrete and steel were examined to determine the composite structural behavior and the extent of predicted damage for the various cases. The observations from these analyses highlighted relationships between the simulation parameters and the corresponding outcome. Conclusions and recommendations are presented that could assist in the development of efficient numerical simulations in this general area.     

A shape optimization study for tool design in resistance welding

The purpose of this study is to apply shape optimization tools for design of resistance welding electrodes. The numerical simulation of the welding process has been performed by a simplified FEM model implemented in COMSOL. The design process is formulated as an optimization problem where the objective is to prolong the life-time of the electrodes. Welding parameters like current, time and electrode shape parameters are selected to be the design variables while constraints are chosen to ensure a high quality of the welding. Surrogate models based on a Kriging approximation has been used in order to simplify the calculation of shape sensitivities and to generate a generic tool that can be interfaced with other simulation tools. An example numerical study shows the potential of applying optimal design techniques in this area. Part of this work was presented at WCSMO7 in Seoul Korea, May 21–25, 2007, in the paper titled ‘Some optimization aspects of resistance welding’ (CD-ROM, pp 2687–2695).     

A partial hybrid stress solid-shell element for the analysis of laminated composites

In this paper we introduce a low order partial hybrid stress solid-shell element based on the composite energy functional for the analysis of laminated composite structures. This solid-shell element has eight nodes with only displacement degrees of freedoms, and three-dimensional constitutive models can be directly employed in the present formulation without any additional treatment. The assumed interlaminar stress field provides very accurate interlaminar stress calculation through the element thickness. These elements can be stacked on top of each other to model multilayer structures, fulfilling the interlaminar stress continuity at the interlayer surfaces and zero traction conditions on the top and bottom surfaces of the laminate. The present solid-shell does not show the transverse shear, trapezoidal and thickness locking phenomenon, and passes both the membrane and the bending patch tests. To assess the present formulation’s accuracy, a variety of popular numerical benchmark examples related to element convergence, mesh distortion, shell and laminated composite analyses are investigated and the results are compared with those available in the literature. The numerical results show the accuracy of the presented solid-shell element for the analysis of laminated composites.     

双丝脉冲MIG焊的工艺特点与试验分析

研究利用高速摄像和电信号观察熔滴过渡过程,确定采用脉冲喷射过渡方式,可获得稳定的焊接过程,并对不同焊接参数下单丝焊和双丝脉冲MIG焊的熔敷速度和焊缝成形进行了对比分析。研究结果表明,在相同焊接质量条件下,双丝焊的焊接效率明显高于单丝焊,焊缝成形系数更好,减小了由于高速焊接造成的产生咬边的可能性。实验所测的焊缝宽度,与预测焊缝宽度的三维模拟方程的模拟值基本一致。     

Multiaxial ratcheting evaluation of functionally graded cylindrical shell by means of Ohno–Wang’s type models

In the present paper, the ratcheting responses of functionally graded (FG) pipe by means of nonlinear kinematic hardening rules of the Ohno–Wang (O–W), McDowell, Jiang–Sehitoglu (J–S) and Chen–Jiao–Kim (C–J–K) models are investigated. The FG pipe is considered to be subjected to a broad class of non-proportional/proportional with different loading types including tension–torsion, tension/thermal–internal pressure with different loading sequences and directions. In the current constitutive models of FG pipe, not only the physical and mechanical properties are variables but also the coefficients of the kinematic hardening rules vary as a power law through thickness. An implicit integration scheme implemented within user subroutine UMAT in ABAQUS/standard is presented for the relatively complicated constitutive models. Comparing with the novel experiments and available results in the literature, the predicted results by the proposed numerical method are demonstrated to be reliable. Results reveal the significant influences of the adopted hardening rules incorporated in the constitutive model and also FG inhomogeneity constant on the multiaxial ratcheting responses of FG pipe.

     

Process parameter optimization of lap joint fillet weld based on FEM–RSM–GA integration technique

This study introduces a welding process design tool to determine optimal arc welding process parameters based on Finite Element Method (FEM), Response Surface Method (RSM) and Genetic Algorithms (GA). Here, a sequentially integrated FEM–RSM–GA framework has been developed and implemented to reduce the weld induced distortion in the final welded structure. It efficiently incorporates finite element based numerical welding simulations to investigate the desired responses and the effect of design variables without expensive trial experiments. To demonstrate the effectiveness of the proposed methodology, a lap joint fillet weld specimen has been used in this paper. Four process parameters namely arc voltage, input current, welding speed and welding direction have been optimized to minimize the distortion of the structure. The optimization results revealed the effectiveness of the methodology for welding process design with reduced cost and time.     

基于主S-N曲线的带止裂槽焊接接头疲劳寿命预测及改进

以带止裂槽焊接接头为研究对象,提取可能发生疲劳失效的焊趾截面、焊喉截面和止裂槽截面的节点力,基于主S N曲线法求解截面的等效结构应力,评估焊缝的疲劳寿命,并提出改进接头的建议。分析发现：止裂槽的存在会显著增加局部位置的应力,导致疲劳寿命明显降低。填充止裂槽并适当增大水平方向焊脚尺寸,可以提高该位置疲劳寿命10倍左右。     

基于几何结构失真模型的图像质量评价研究

客观图像质量评价研究的目的是设计一种和视觉感知保持一致,且适用于各种失真模型的质量评价方法. 传统的结构相似度量质量评价方法忽视了自然图像本身的特点,不能很好地评判某些失真类型图像. 本文根据人眼视觉系统(Human visual system, HVS)在感知图像质量过程中的特点,探索自然图像的本征几何结构特征, 考虑像素点的方向失真、幅度失真和方差失真,提出了一种新型的基于图像几何结构失真模型的完全参考质量评价方法. 在标准数据库上的实验结果表明,本文方法适用于所有失真模型图像数据的质量评价, 计算复杂度相对较低,得到的图像客观评价结果和主观评价方法具有更好的一致性, 能够很好地反映人眼对图像质量的主观感受.     

前机身/进气道流场的一体化数值模拟

该文针对飞行器设计中的机体和进气道的一体化问题,采用分区结构搭接网格技术,对机体外流场采用有限体积法求解Euler方程,进气道内流场采用有限体积法求解N—S方程,发展了求解三维超音速前机身／进气道内外流的Euler／N—S方程分区处理程序,同时对某型飞机的前机身／进气道流场进行了一体化模拟。通过分析计算出的附加阻力和畸变系数等结果的合理性验证了计算程序的正确性。同时通过对计算域采用不同的密度网格进行计算,分析研究了网格疏密对计算结果的影响。     

磁放大器控制硅弧焊整流器性能的研究

本文针对硅弧焊整流器的控制性能,在分析铁磁材料特性的基础上,分别对单铁芯磁放大器和双铁芯磁放大器的结构和工作原理进行了深入的研究,提出了单铁芯磁放大器所存在的缺点以及双铁芯磁放大器的优点,使得硅弧焊整流器的设计采用双铁芯磁放大器,能够避免焊接时焊接电流波形的畸变,对提高焊接质量是有利的。