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.

Effects of welding parameters and welding sequence on residual stress and distortion in Al6061-T6 aluminum alloy for T-shaped welded joint

The distribution of temperature and then the distribution of residual stress and distortion in the stiffened aluminum alloy Al6061-T6 plates under the metal inert gas(MIG)welding process were investigated by three dimensional thermo-mechanical coupled finite element model using Ansys software.The properties of materials were considered temperature-dependent and the filler metal was added to the workpiece by the element birth and death technique.In three modes of current,two different speeds and two various sequences,the distribution of residual stress and distortion were calculated and analyzed.The results showed that increase in welding speed decreased the vertical deflection in the plate,transverse shrinkage and angular distortion of plate and the lateral deflection of stiffener,but increased the maximum longitudinal tensile stress in the plate and stiffener.Furthermore,increase in current increased the residual stress and deformation in the plate and stiffener,and the change in the welding sequence changed the distribution of the distortion in the plate and the stiffener without significant change in the distribution of the longitudinal residual stress.

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.

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.

NUMERICAL SIMULATION OF CONTROLLING IN TITANIUM ALLOY SHEETS WELDING RESIDUAL STRESS BY TRAILING PEENING

It is a promising and new technology to apply welding with trailing peening to control welding stress and distortion of titanium alloy.Numerical simulation of conventional welding and welding with trailing peening of the titanium alloy sheet is carried out,using nonlinear finite element theory and the engineering analysis software MARC.The result shows that welding with trailing peening technology reduces longitudinal residual stress in welding joint effectively,and it is more effective to reduce residual stress to peen the weld than to peen the weld toe.It is a effective result that other technology and method used in welding can never achieved.

3D FEM analysis of welding residual stress and deformation of aero-engine blisk

Aero-engine blisk welded by electron beam welding（EBW） method is a complicated structure. Fixtures were used to control the deformation of blisk during its manufacturing process. Finite element method was utilized to study the evolution of the welding residual stress and deformation of this structure. In which an attenuation function was applied to the double ellipsoid heat source model based on the characteristic of EBW, and the effects of fixtures on the welding residual stresses and deforamtion were also reserached. The simulation results showed that the temperature contour of weld cross section vertical to the weld centerline followed a ＇＂ V＂ shape. Moreover, large welding residual stress and distortion were found in the interface between blisk and fixtures. The stress concentration was reduced sufficiently in starting and end part of weldment as the fixtures were renmved after welding process, while the removing operation had almost no effects on the welding residual stress in the middle section of weld bead.

FEM Simulation of Distortion and Residual Stress Generated by High Energy Beam Welding with Considering Phase Transformation

A series of experiments was carried out so as to elucidate the effect of the phase transformation in the cooling process on welding distortion and residual stress generated by laser beam welding (LBW) and laser-arc hybrid welding (HYBW) on the high strength steel (HT780). Then, the experiments were simulated by 3D thermal elasticplastic analysis with FEM (Finite Element Method) which was performed with using the idealized mechanical properties considering the transformation superplasticity. From the results, the effects of the phase transformation on welding distortion and residual stress generated by LBW and HYBW were elucidated. Furthermore, the generality of the idealization of the mechanical properties was verified.

Finite element analysis of the angular distortion and residual stress in underwater wet welding

In underwater environment, the shape, voltage, and energy density of the welding arc vary because of the high pressure and there are notable changes in workpiece cooling conditions due to the strong cooling effect of water. As a result, there are clear differences between the residual stress and thermal distortion in underwater wet welding and those in conventional welding （in air）. Considering these process features, a thermo-mechanical finite element model of underwater wet bead-on-plate welding was established. The influences of the water compressing action to the arc and the enhanced heat losses caused by the surrounding water on the residual stress and the angular distortion of the workpiece were analyzed. Results show that the angular distortion gets smaller in deeper water, and that the longitudinal residual stress gets smaller as water flows faster.

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.

Prediction and Control of Distortion and Residual Stresses in Electron Beam Welding

Electron beam welding is recognized as an attractive method for minimizing distortion during welding,and is used frequently to join parts which are already finally machined or close to finished size.In such cases,before EB welding,it is of great value to be able to estimate the level of accuracy that will be achieved and the dimensional stability of the assembly throughout its service life.This presentation describes the development of a finite element (FE) modelling technique,validated by experiment,for predicting and understanding the development of residual stresses and distortion during EB welding,particularly in circular components.The use of this method for optimization of welding procedures and residual stress mitigation methods is described and illustrated through a number of practical examples.

Thermal Tensioning Effects to Prevent Welding Buckling Distortions in Manufacturing of Thin-Walled Aerospace Shells and Panels

To prevent buckling distortions of thin-walled elements, Low Stress No Distortion welding techniques have been pioneered and developed for product engineering and component manufacturing of aerospace structures with material thickness less than 4 mm. In this paper, the nature of Low Stress No Distortion (LSND) welding techniques using thermal tensioning effects is described and special emphases are given to the mechanism of localized thermal tensioning effect. The fundamental principle of Low Stress No Distortion welding is to create active in-process control of incompatible (inherent) plastic strains and stresses formation during welding to achieve distortion-free results implying that no post weld costly reworking operations for distortion correction is required. Finite element analysis is applied to predict and optimize the localized thermal tensioning technique with a trailing spot heat sink coupled to the welding heat source. Comparisons of the thermal elastic-plastic stress-strain cycles are given between conventional gas tungsten arc welding and GTAW with a trailing spot heat sink.

A new method for welding aluminum alloy LY12CZ sheet with high strength

From the viewpoint of welding mechanics, a new welding technology—trailing peening was applied firstly to weld aluminum alloy LY12CZ sheet with high susceptibility to hot cracking. Trailing peening can exert a transverse extrusion strain on the metal in brittle temperature region (BTR) which can compensate for the tensioning strain during the cooling procedure post welding. So, welding hot cracking of LY12CZ sheet can be controlled effectively on the special jig for hot cracking experiment, and the phenomenon of hot cracking can’t be found in specimens with large dimensions finally. At the same time, welding with trailing peening can decrease welding distortion caused by longitudinal and transverse shrinkage of weld obviously. Due to strengthening the poor position-weld toe during the process of welding, the residual stress distribution of welded joint is more reasonable. Contrast with conventional welding, mechanical properties such as tensile strength, prolongation ratio and cold-bending angle of welded joint with trailing peening can be improved obviously, and rupture position of welded joint transits from weld toe at conventional welding to weld metal at trailing peening. So, welding with trailing peening can be regarded as a dynamic welding method with low stress, little distortion and hot cracking-free really. As far as theoretical analysis is concerned, the technology of trailing peening can be used to weld the materials with high susceptibility to hot cracking such as LY12CZ and LD10, and solve the welding distortion of thin plate-shell welded structures which contain closed welds such as flange. In addition, the technology of trailing peening has many advantages: simple device, high efficiency, low cost and flexible application which make the welding method have widely applied foreground in the field of aeronautics and aerospace.

Correction of buckling distortion by ultrasonic shot peening treatment for 5A06 aluminum alloy welded structure

Ultrasonic shot peening treatment （USPT） was proposed to correct welding buckling distortion. The residual stress distribution along the depth direction of the peened zone was measured by an X-ray diffractometer. The microstructure of the treated specimens was investigated by scanning electron microscopy （SEM）. The Vickers microhardness was measured in different areas of welded joint before USPT and along the depth direction of the weld after USPT. The experimental results indicated that the welding buckling distortion of 5A06 aluminum alloy butt joint can be essentially corrected by USPT; the average correction rate reached 90.8% in this study. Furthermore, USPT enhanced specimens by work hardening. The microstructure of the peened zone was improved; moreover, the distribution of the precipitates and grains presented an apparent orientation.

Low stress no distortion welding for aerospace shell structures

To fit in with the strict geometrical integrity and ensure dimensionally consistent fabrication of the welded aerospace structures. the low stress no distortion(LSND)welding, a technique for thin materials, was poineered and developed to provide an ininprocess active control of welding distortion. Satisfactory distortion free results were achieved in both welding of jet engine cases of heat-resistance alloys and rocket fuel tanks of aluminuim alloys, and there need no. reworking operations for post-weld distortion correction. Based on the 'static' method a newly developed method for dvnamic in-process control is also discussed in this paper. Both methods provide quanutiative in-process control of incompatible strains in weld zone and low stress no distortion welding results.

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.

A Finite Element Model to Investigate the Impact of Torch Angle on an Autogenous TIG Welding Process

A numerical modelling activity was completed to explore the impact that the angle θ created by the torch from the vertical had upon the thermal and mechanical predictions for a T-joint autogenous TIG welded component. A parametric system of 9 models was set-up to simulate the effects of varying the angle θ by a small, potentially unnoticeable amount to a manual operator. The variations ranged from -8° to +8° away from a nominal default position of torch. The numerical models were created and computed using specialist welding simulation software Sysweld, and pre/post-processing software Visual Environment (both owned by ESI Group). The resulting weakly-coupled thermal and mechanical analyses illustrated a small deflection of angle that the weld bead was penetrating in to the T-joint, consistent with the variation in torch angle, and a negligible variation in peak temperature of 1.8%. The mechanical results however demonstrated a more significant output, namely that the distortion observed upon the vertical plate within the T-joint was predicted to increase by over 50% as result of this small shift in the welding torch angle. However, other mechanical predictions for plastic strain, Von Mises residual stress and distortion on the horizontal plate, were all suggesting only very minor sensitivity (typically less than 5%) to the torch angle variation. However, the predictions for vertical plate distortions demonstrate how difficult a manual TIG operation can be to perform with sufficient process control and repeatability, due to the significant impact that human operator-induced variation has upon some of the mechanical outputs.

Numerical Analysis of Welding Residual Stress and Distortion in Laser+GMAW Hybrid Welding of Aluminum Alloy T-Joint

A 3-D finite element model is developed to predict the temperature field and thermally induced residual stress and distortion in laser＋GMAW hybrid welding of 6061-T6 aluminum alloy T-joint. And the characteristics of residual stress distribution and deformation are numerically investigated. In the simulation, the heat source model takes into account the effect of joint geometric shape and welding torch slant on the heat flux distribution and a sequentially coupled thermo-mechanical method is used. The calculated results show that higher residual stress is distributed in and surround the weld zone. Its peak value is very close to the yield strength of base metal. Besides, a large deformation appears in the middle and rear part of the weldment.

船体板架纵骨错位对焊接变形及应力的影响

在船体板架的焊接工序中,由于制造误差产生的纵骨错位问题对焊接过程及焊接质量产生不利影响。以典型船体板架为例,在纵骨强制对齐的基础上采用顺序耦合的热弹塑性有限元法对其焊接过程进行数值仿真分析,研究纵骨错位量对焊接变形和应力的影响规律。结果表明,随着错位量的增加,错位纵骨两侧板格焊接变形分布的不对称性逐渐增强,左右两侧板格变形差值最大可增加3.7倍,且当错位量一定时,外板厚度越小纵骨错位的影响越大。此外,纵骨强制装配产生的应力与板架焊后残余应力均随错位量的增大而增加,当错位量为10 mm时,残余拉应力与压应力分别是纵骨未错位情况下的4.4倍与4.9倍。

Rational Design of T-Girders via Finite Element Method

The main configuration of ship construction consists of standard and fabricated stiffening members,such as T-sections,which are commonly used in shipbuilding.During the welding process,the nonuniform heating and rapid cooling lead to welding imperfections such as out-of-plane distortion and residual stresses.Owing to these imperfections,the fabricated structural members may not attain their design load,and removing these imperfections will require extra man-hours.The present work investigated controlling these imperfections at both the design and fabrication stages.A typical fabricated T-girder was selected to investigate the problem of these imperfections using double-sided welding.A numerical simulation based on finite element modeling(FEM) was used to investigate the effects of geometrical properties and welding sequence on the magnitude of the welding imperfections of the T-girder.The FEM results were validated with the experimental measurements of a double-sided fillet weld.Regarding the design stage,the optimum geometry of the fabricated T-girder was determined based on the minimum steel weight and out-of-plane distortion.Furthermore,regarding the fabrication stage,a parametric study with two variables(geometrical properties and welding sequence)was conducted to determine the optimum geometry and welding sequence based on the minimum welding out-of-plane distortion.Increasing the flange thickness and reducing the breadth while keeping the T-girder section modulus constant reduced the T-girder weight and out-of-plane distortion.Noncontinuous welding produced a significant reduction in the out-of-plane distortion,while an insignificant increase in the compressive residual stress occurred.

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。