Analysis of residual stress in stainless steel pipe weld subject to mechanical axial tension loading

This paper presents the characteristics of welding residual stresses in circumferentially butt-welded stainless steel pipe by utilizing three-dimensional (3-D) uncoupled thermo-mechanical finite element (FE) analysis method. Moreover, stress variations in welded joints of the pipe under superimposed mechanical axial tension loading are further investigated employing the welding residual stresses and plastic strains obtained from the thermo-mechanical FE analysis as an initial condition. Results show that spatial variations of the welding residual stresses are present along the circumference and a rapid change of the residual stresses exists at the welding start/stop position, hence 3-D FE analysis is essential to accurately simulate circumferential welding of a pipe component. When mechanical axial tension loading is applied to the circumferentially butt-welded stainless steel pipe, bending moment is generated at the welded joints caused by the circumferential shrinkage of the weld region during welding; thus affecting the axial and hoop stress evolutions in the course of the superimposed mechanical loading.     

Column curves for elliptical hollow section members

A thermo-mechanical finite element analysis model is developed to predict residual stress patterns in hot-rolled sections. The model is first verified against experimental measurements for residual stresses reported for I-sections reported in the literature. The method is then used to predict residual stresses in elliptical hollow sections. A sensitivity analysis is then conducted to assess the influence of various input parameters of the model on the predicted residual stress patterns. The effects of cross-section geometric parameters on the residual stress distribution are then investigated.A series of column curves is generated providing the compressive capacity of a column as a function of slenderness. The column curves are generated based on a) elasto-plastic geometrically nonlinear analyses, b) including the effect of residual stresses as predicted from thermo-mechanical analyses and c) incorporating initial geometric out-of straightness according to the fundamental buckling mode as predicted from an elastic buckling eigen value analysis. Generated column curves are then compared to those in current design codes. A best fit for the numeric results obtained is conducted to cast them in a format similar to that in the current codes.     

Proposed residual stress model for roller bent steel wide flange sections

The manufacturing process of structural wide flange steel sections introduces residual stresses in the material. These stresses due to hot-rolling or welding influence the inelastic buckling response of structural steel members and need to be taken into account in the design. Based on experimental data standardized residual stress models have been proposed for inclusion in inelastic buckling analyses. By incorporating these residual stress models their effect on the resistance of beams and columns can be obtained. Residual stress models for roller bent steel sections are currently not available. Roller bent wide flange sections are manufactured by curving straight members at ambient temperature. This manufacturing technique, which is also known as roller bending, stresses the material beyond its yield stress, thereby overriding the initial residual stresses prior to bending and generating an entirely new pattern. This paper proposes a residual stress model for roller bent wide flange sections, based on earlier conducted numerical investigations which were validated by experimental research performed at Eindhoven University of Technology. The proposed residual stress model can serve as an initial state of a roller bent steel section in fully non-linear finite element analyses to accurately predict its influence on the inelastic buckling response.     

Bending capacity of girth-welded circular steel tubes

In this paper, the buckling behavior of girth-welded circular steel tubes subjected to bending was investigated by numerical method. Finite element (FE) simulation of the girth welding process was first performed to obtain weld-induced residual stress and deformation employing sequentially coupled three-dimensional (3-D) thermo-mechanical FE formulation. Elastoplastic large-deformation analysis in which the failure mode, the ultimate moment capacity and the moment versus end-rotation behavior of girth-welded circular steel tubes under pure bending were explored incorporating weld-induced geometric imperfection and residual stress was next carried out. Results showed that the flexural behavior of girth-welded circular steel tubes always involves local buckling near the girth weld on the compression side, which significantly affects the moment versus end-rotation response.     

圆形焊接钢管的弯曲性能

采用数值计算方法对圆形焊接钢管的弯曲性能进行研究。用有限元(FE)法模拟环缝的焊接过程,采用三维(3D)热力耦合FE模型得到焊接残余应力和变形。结合焊接引起的几何缺陷和残余应力,对焊接圆钢管的失效模式、抗弯承载能力以及纯弯曲状态下的端部扭转性能进行了弹塑性大变形分析。结果表明,圆形焊接钢管的弯曲性能包含邻近焊缝处受压区的局部屈曲,这对端部扭矩有着显著影响。     

栓焊混合连接狗骨式梁柱钢节点残余应力有限元分析

焊接作为结构连接的一种重要形式被广泛应用于钢结构中.焊接过程中由于温度梯度产生的焊接残余应力,给实际工程安全带来很大的威胁,所以研究钢结构在焊接过程中产生的残余应力是十分必要的.利用有限元数值模拟软件ANSYS建立狗骨式梁柱节点顶底角钢、焊缝、螺栓混合连接的三维有限元模型,模拟梁柱节点焊接的温度场,在热弹塑性理论基础上求解焊接残余应力.结果表明：构件在焊接过程中主要受拉,并且在不同位置的应力各不相同.由于狗骨式节点的存在,削弱了节点对梁部分的约束.在梁上翼缘螺栓上出现焊接残余应力的最大值,在腹板角钢与柱连接的中间螺栓处出现最小值.这与规范中的规定基本相符.     

Fatigue life evaluation of welded joints considering the local multiaxial stress/strain states and numerically determined residual stresses/strains

This paper puts forward a kind of calculation method of estimating fatigue crack initiation life by considering welding residual stresses as initial stresses. The numerical method could be used to quantitatively analyze the influence of residual stresses on the cumulative fatigue damage. In order to gain the distribution of weld-induced residual stresses, the FE analyses as well as measurements were carried out. Based on critical plane approach, analysis of damage parameters was performed considering both welding residual stress and biaxial loads. Subsequently, validity of the proposed numerical method is verified by analyzing fatigue test results for several typical welded joints. It is concluded that the result of the present method is closer to the experimental value than that obtained with empirical formula method in the estimation of fatigue crack initiation life of welded structures.     

钢管相贯K型节点焊接残余应力的数值模拟与试验分析

钢管相贯焊接节点是空间钢管桁架的常见连接方式,为了深入研究钢管相贯节点的极限承载力和疲劳寿命,对K型钢管相贯节点的残余应力进行了分析。针对K型钢管相贯节点焊接时的热应力特征,通过对焊接过程中加热与冷却温度场的正确描述,并采用相应的热传导数学和物理模型,进行温度场和应力场的耦合计算。计算中考虑了钢材热物理参数和力学参数随温度变化的非线性性能,得到的残余应力和残余变形分布规律与K型钢管相贯节点试验的破坏形态吻合较为理想,据此提出焊接热损伤对节点破坏形式有一定影响的观点。     

Experimental study on residual stresses in welded monosymmetric I-section

为了研究单轴对称焊接工字形截面残余应力分布规律,采用盲孔法对15个单轴对称工字形截面试件进行了试验研究,得到了不同试件全截面纵向残余应力分布,研究了腹板高厚比、翼缘宽厚比、翼缘宽度、施焊顺序等对残余应力的影响。试验结果表明：残余压应力数值与截面尺寸直接相关,残余拉应力数值受截面尺寸影响较小;腹板中靠近宽翼缘一侧的残余压应力峰值大于靠近窄翼缘一侧的压应力峰值;翼缘宽度增大时,分布于所在翼缘和腹板的残余压应力减小;施焊顺序对翼缘上的残余应力及腹板上的残余拉应力峰值有一定影响,而腹板上的残余压应力没有明显变化。基于试验结果,提出了适用于单轴对称焊接工字形截面的残余应力分布模型,该模型能够较准确反映各种因素的影响。     

Schweißen unter Betriebsbeanspruchung – Numerische und experimentelle Bestimmung des Temperaturfeldes beim Schweißen

Welding under service loads – numerical and experimental assessment of temperature fields due to welding. The experimental determination of temperature fields due to welding gives only rough information about the residual stresses in the vicinity of the sensor. An experimental time dependent determination of a quickly changing temperature field is almost impossible. The paper describes the basics of a numerical temperature field determination due to MAG‐welding. The result of the temperature field determination serves as an input for the assessment of the mechanical residual stresses. A comparison of theoretical and experimental results are given.     

Effect of start/stop position distribution on residual stresses in the multi-pass welded 12Cr1MoV/P91 dissimilar pipe

Welding residual stresses between 12Cr1MoV and P91 steel pipes were analyzed by experiment and finite element method (FEM). Both measured hoop and axial stresses are in general agree with the simulation results. Meanwhile, to examine the effect of start/stop welding position on residual stresses, a simulation model whose welding passes all started at the same location during multi-pass welding was compared with a model whose start/stop positions were uniformly distributed along circumferential direction of the dissimilar pipe. The results show that higher residual stresses occurred near the superimposed start/stop position than the steady region when calculated by the model whose welding passes all started at the same location. Whereas, start/stop welding positions which are distributed uniformly along the circumferential direction of the pipe can significantly relieve this effect, correspondingly leading to a more uniform residual stress distribution around the multi-pass welded dissimilar pipe.     

A preliminary structural design procedure for laser beam welded airframe stiffened panels

Initial sizing procedures for aircraft stiffened panels that include the influence of welding fabrication residual process effects are missing. Herein, experimental and Finite Element analyses are coupled to generate knowledge to formulate an accurate and computationally efficient sizing procedure which will enable designers to routinely consider panel fabrication, via welding, accounting for the complex distortions and stresses induced by this manufacturing process. Validating experimental results demonstrate the need to consider welding induced material property degradation, residual stresses and distortions, as these can reduce static strength performance. However, results from fuselage and wing trade-studies, using the validated sizing procedure, establish that these potential reductions in strength performance may be overcome through local geometric tailoring during initial sizing, negating any weight penalty for the majority of design scenarios.     

Q460C高强度钢柱滞回性能有限元分析

为进一步研究Q460C高强度钢柱的滞回性能,在已有试验研究的基础上,采用通用有限元分析软件ANSYS建立了数值模型,对Q460C高强度钢材焊接箱形和H形截面柱在常轴力和水平往复荷载作用下的滞回性能进行模拟,并研究了残余应力对高强度钢试件滞回性能的影响。将有限元分析结果与已有试验结果进行对比,两者吻合较好。研究结果表明：采用提出的Q460C高强度结构钢滞回模型进行有限元分析,能较为准确的预测Q460C高强度钢材焊接H形和箱形柱的滞回性能;试件内残余应力对Q460C高强度钢材焊接H形和箱形截面柱的滞回性能影响较小。     

热应力法在钢结构焊接疲劳模拟中的应用

基于ANSYS平台,给出了间接热应力法计算焊接残余应力的计算流程。以V型坡口钢板为例,利用APDL语言编程,获得了焊接温度场及残余应力场的分布规律,计算结果与实测结果比较吻合。对于进一步研究焊接疲劳具有指导意义。     

A simplified FE simulation method with shell element for welding deformation and residual stress generated by multi-pass butt welding

In order to propose a simplified simulation method using finite element (FE) model for predicting deformation and residual stress generated by multi-pass butt welding, a series of experiments and numerical analyses were carried out. 3-pass butt welding of steel plates was simulated by the thermal elasto-plastic analysis with shell elements and with solid elements respectively. A heat input model for considering the temperature distribution in the thickness direction in shell elements was proposed. The validity of the heat input model was verified by comparing analytical results with experimental results or other analytical results using solid elements. Furthermore, the effectiveness for saving computing time by using shell elements was confirmed from the comparison with the case using solid elements. It was confirmed that the welding out-of-plane deformation and residual stress could be predicted with high accuracy by the proposed method. The computing time was around 14% of that by the precise model with solid elements.     

焊接残余应力对焊接结构的影响

焊接残余应力是焊件产生变形和开裂等缺陷的主要原因,由于其影响因素众多,本文分别从焊接残余应力对结构的刚度、受压杆件稳定性、静载强度、疲劳强度、构件脆性、焊件加工精度和尺寸稳定性等方面进行分析研究残余应力对焊接结构产生的影响。     

Residual stresses in cold-rolled stainless steel hollow sections

Stainless steel exhibits a pronounced response to cold-work and heat input. As a result, the behaviour of structural stainless steel sections, as influenced by strength, ductility and residual stress presence, is sensitive to the precise means by which the sections are produced. This paper explores the presence and influence of residual stresses in cold-rolled stainless steel box sections using experimental and numerical techniques. In previous studies, residual stress magnitudes have been inferred from surface strain measurements and an assumed through-thickness stress distribution. In the present study, through-thickness residual stresses in cold-rolled stainless steel box sections have been measured directly by means of X-ray diffraction and their effect on structural behaviour has been carefully assessed through detailed non-linear numerical modelling. Geometric imperfections, flat and corner material properties and the average compressive response of stainless steel box sections were also examined experimentally and the results have been fully reported. From the X-ray diffraction measurements, it was concluded that the influence of through-thickness (bending) residual stresses in cold-rolled stainless steel box sections could be effectively represented by a rectangular stress block distribution. The developed ABAQUS numerical models included features such as non-linear material stress-strain characteristics, initial geometric imperfections, residual stresses (membrane and bending) and enhanced strength corner properties. The residual stresses, together with the corresponding plastic strains, were included in the FE models by means of the SIGINI and HARDINI Fortran subroutines. Of the two residual stress components, the bending residual stresses were found to be larger in magnitude and of greater (often positive) influence on the structural behaviour of thin-walled cold-formed stainless steel sections.     

Experimental and FE analysis of submerged arc weld induced residual stress and angular deformation of single and double sided fillet welded joint

Submerged arc welding is well-known for its very high deposition rate and thus the capability to join very high thickness metal pieces in large structural applications. Fillet joints are mostly used in structural applications which can be extensively seen in shipbuilding, bridge construction, house buildings, automobile or any other large structures. Thermal stresses generates in a fusion welded joint due to high temperature gradient, which is the cause of the residual stresses upon cooling followed by the angular deformation and failure of the welded structure. As an effect of the thermal gradient, the induced longitudinal, transverse residual stress & angular distortion can vary in single sided and double sided submerged arc welded fillet joints, during designing & manufacturing welded structures which should be taken into account. The main objective of this paper is to quantify the amount of residual stresses and angular deformation in a fillet welding joint. An elasto-plastic thermomechanical model has been developed for predicting residual stresses. A comparison of the residual stress and angular deformation between single and double sided fillet weld joint has been made. The simulation results reveal that the amount of residual stress present in the single sided fillet weld is more and unbalanced in both side of the center of weld line compared to the double sided fillet weld and the predicted results have been matched with the experiments as well as published literatures.     

A study on the effect of weld groove designs on residual stresses in SS 304LN thick multipass pipe welds

Present research describes the effect of weld groove designs on residual stresses of thick SS 304LN pipe welds which are commonly utilized for applications such as boiling water reactor system, oil and steam piping. The faying surfaces of the pipe joints were machined to generate conventional and narrow groove geometries for welding. Circumferential multipass pipe welding was carried out without applying preheat and post weld heat treatment. Blind hole drilling technique was employed for measuring hoop and axial residual stresses in narrow and conventional grooved SS 304LN pipe welds considering plasticity and stress concentration effects of hole drilling process. The result exhibited 20 to 30 percent reduction in residual stresses in narrow grooved pipe welds. A finite element model was developed for estimating the pass by pass peak temperature distributions in the pipe welds. Sequentially coupled thermomechanical elastic-plastic analysis of both conventional and narrow groove pipe welds indicated close agreement between the predicted and experimentally determined hoop and axial residual stresses.     

基于盲孔法的高强焊接圆钢管表面残余应力试验研究

为研究高强焊接圆钢管残余应力分布模式,基于盲孔法对21个高强焊接圆钢管的5个外表面、1个端部内表面纵向残余应力分布进行测量;对盲孔法应变释放系数A、B进行平面试验及平面有限元标定,验证有限元标定的可靠性;进行柱面有限元标定并依据形状改变比能修正法对试验测量结果进行塑性修正,提出埋弧焊接、高频焊接圆钢管外表面纵向残余应力分布模型。研究结果表明：柱面有限元模型可弥补应变计弧面形状造成的误差,与平面试验标定结果相比,对于截面规格为■325×8的埋弧焊接圆钢管标定系数A误差可达6.1%,对于截面规格为■356×10的埋弧焊接圆钢管,标定系数B误差可达5.0%;与平面有限元模型标定结果相比,由柱面标定得到的应变释放系数A随直径增大而减小、系数B随直径增大而增大,并逐步趋近于平面标定结果。沿着焊接方向1/4、1/2、3/4柱高截面最大纵向残余应力数值相近,最大残余拉、压应力分别为0.96■、-0.27■。高频焊接圆钢管端部内表面与外表面残余应力分布模式不同,外表面以残余拉应力为主且最大为0.46■,内表面以残余压应力为主且最大为-0.37■。提出的纵向残余应力分布模型与实测数据吻合较好。