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.     

Experimental and numerical investigations on residual stresses in a multi-pass butt-welded high strength SM570-TMCP steel plate

During fusion welding process, complex thermal stresses are inevitably generated. The presence of residual stresses can be detrimental to the integrity and the service behavior of the welded part. In this study, both an experiment and a finite element (FE) method were utilized to investigate residual stress distribution in high strength SM570-TMCP (thermo-mechanical controlled process) steel weldment, which was constructed using a multi-pass butt welding process. Firstly, experiments which included a tensile test at elevated temperatures, an observation of the microstructures and a residual stress measurement were carried out to examine characteristics of residual stresses in the weldment. Secondly, a three-dimensional thermo-mechanical FE model was developed to simulate the temperature field and the residual stress field incorporating the experimental results. The thermo-mechanical model used as well as the experimental procedure is described in detail, and the results obtained from the FE model are compared with the experimental measurements and discussed.     

Numerische Analyse geschweißter Verbindungen von Duplexstahl und Quarzglas

Numerical analysis of welded joints between duplex steel and quartz glass. Welded joints are a vital element in structural engineering. Originating from conventional carbon steel welding in construction, recent advancements in welding technology now allow the joint of modern high‐strength steel and glass materials. With today's methods, an analysis of the welded joints' structural behaviour can be conducted by experiment, as well as by numerical analysis. Particularly for the numeric analysis, capturing the non‐linear thermal and mechanical properties of the materials is important, in order to allow a realistic determination of temperature, microstructure and residual stresses for different types of joints. Simulations of multi‐layered weld joint on duplex steel show, that a targeted heat treatment during MAG‐welding by variation of the welding parameters achieves a beneficial ratio between ferrite and austenite which, for example, ensures a high resistance of the weld to corrosion. The material quartz glass can generally be welded as butt‐weld with a CO₂‐laser. The simulations of a welded joint of a plate and a pipe show, that an optimization of the welding technology of preheat laser beam and welding laser beam is necessary, in order to reduce the thermal impact during the welding process, as well as residual stress in the joint. At the Department of Steel Structures at the Bauhaus‐Universität Weimar, numerical simulations of welded joints between steel and glass materials are a current and topical research focus.     

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。     

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。     

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.     

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.     

圆弧焊接薄壁圆筒残余应力场的分析研究

由于圆弧焊接的薄壁圆筒在高科技工程,如航空机器、压力容器和核工程中的广泛应用,对焊接导致的如焊接变形和残余应力等缺陷的研究就显得非常重要。介绍了一个计算程序,用以分析低碳钢薄壁圆筒在圆弧焊接中的温度分布以及随后将产生的残余应力场。基于数值模拟的参数研究用于分析焊接所产生的残余应力中的关键参数的影响。考虑了低碳钢、焊丝和双椭圆热源模型的基于温度的热机械性能。通过全尺寸焊接试验中的瞬时温度分布和残余应力场证实了有限元模拟方法的精确性。其目的在于提供数据以证实薄壁圆筒现有焊接工艺的有效性,从而将预加应力导致的结构在使用期间失效的可能性降至最低。     

Influence of welding residual stresses on the ductile crack growth resistance of circumferentially cracked pipe

Welding residual stress is one of the main concerns for fabrication and operation of steel structures due to its potential effect on structural integrity. This paper focuses on the effect of welding residual stress on the ductile crack growth resistance of circumferentially cracked steel pipes. Two-dimensional axi-symmetry model has been used to simulate the pipe. Residual stresses were introduced into the model by using so-called eigenstrain method. The complete Gurson model has been employed to calculate the ductile crack growth resistance. Results show that residual stresses reduce the ductile crack growth resistance. However, the effect of residual stresses on ductile crack growth resistance decreases with the increase of crack growth. The effect of residual stress has also been investigated for cases with different initial void volume fraction, material hardening and crack sizes.     

薄壁钢管残余应力有限元分析

根据热弹塑性应力理论、有限元增量理论 ,利用大型有限元软件ANSYS对直焊缝薄壁钢管进行残余应力分析 ,分析结构表明 ,焊接中心残余拉应力最大 ,截面上拉压应力交替出现 ,并与试验结果相比 ,吻合较好 ,为残余应力的理论分析提供参考。     

Fatigue Resistance Improvement of Welded Joints by Bristle Roll-Brush Grinding

In the periodic repainting of steel bridges, often the steel surface has to be prepared by using power tools to remove surface contaminants, such as deteriorated paint film and rust, and to increase the adhesive strengths of the paint films to be applied newly. Surface preparation by bristle roll-brush grinding, which is a type of power tool, may additionally introduce compressive residual stress and increase the fatigue resistance of welded joints owing to the impact of rotating bristle tips. In this study, fatigue tests were conducted for longitudinally out-of-plane gusset fillet welded joints and transversely butt-welded joints to evaluate the effect of bristle roll-brush grinding prior to repainting on the fatigue resistance of the welded joints. The test results showed that bristle roll-brush grinding introduced compressive residual stress and significantly increased fatigue limits by over 50%.     

Experimental and Numerical Study on Complex Multi-planar Welded Tubular Joints in Umbrella-Type Space Trusses with Long Overhangs

A test rig with multi-functional purposes was specifically designed and manufactured to study the behavior of multi-planar welded tubular joints subjected to multi-planar concurrent axial loading. An experimental investigation was conducted on full-scale welded tubular joints with each consisting of one chord and eight braces under monotonic loading conditions. Two pairs or four representative specimens (two specimens for each joint type) were tested, in which each pair was reinforced with two kinds of different internal stiffeners at the intersections between the chords using welded rectangular hollow steel sections (RHSSs) and the braces using rolled circular hollow steel sections (CHSSs) and welded RHSSs. The effects of different internal stiffeners at the chord–brace intersection on the load capacity of joints under concurrent multi-planar axial compression/tension are discussed. The test results of joint strengths, failure modes, and load–stress curves are presented. Finite element analyses were performed to verify the experimental results. The study results show that the two different joint types with the internal stiffeners at the chord–brace intersection under axial compression/tension significantly increase the corresponding ultimate strength to far exceed the usual design strength. The load carrying capacity of welded tubular joints decreases with a higher degree of the manufacturing imperfection in individual braces at the tubular joints. Furthermore, the interaction effect of the concurrent axial loading applied at the welded tubular joint on member stress is apparent.     

On the estimation and control of welding distortion of guide blade carrier for a 660 MW turbine by using inherent strain method

While predicting the welding distortion for a complex welded structure like the guide blade carrier assembly of power generation turbine, the traditional thermo-mechanical models commonly utilized for geometrically simple welded butt and T joints may not be adequate. For large and complex welded structures,the thermo-mechanical elasto-plastic analysis can be computationally prohibitive. Other than simplistic butt and T joints, the aforementioned distortion prediction technique is not so suitable to provide reliable results when applied to large complex 3-D welded structures. Hence, inherent strain method is proposed here to predict distortion in an outer ringof GBC (Guide Blade Carrier) of a steam turbine. Such welded outer rings of GBC are large welded structures having many welded joints of different weld geometries at several planes. In the present study, inherent strain based technique was utilized for the aforementioned welded structure in elastic finite element analysis for the accurate prediction of 3-D distortion patterns with reduced computational time. The predicted and measured values of 3-D distortions of GBC were observed to be in good agreement with the ones provided from the shop floor, indicating the adequacy of inherent strain based method for the prediction of welding distortion in large and complex welded structures. As part of this investigation, a suitable welding fixture was also designed and welding sequence was modified, which were verified through inherent stain method to aid in minimizing the distortion of welded GBC.     

Optimization-improved thermal–mechanical simulation of welding residual stresses in welded connections

This paper presents a novel computer-aided computational framework to determine the optimum shape parameters in a welding heat source model using a coupled supervised Gaussian process regression (GPR) and genetic algorithm (GA) approach in estimating the welding residual stresses. The experimental X-ray diffraction (XRD) approach validates the optimization-improved thermal–mechanical simulation method. The validation of the proposed approach includes the welded plates with simple geometry to welded pipe-to-plate and the circular hollow section joints with complex topologies. The optimization-derived shape parameters in a welding heat source model lead to close estimates of the temperature history and the welding residual stresses for these types of welded joints considered in this study.     

奥氏体316不锈钢焊接工字形截面残余应力的试验研究

不锈钢在建筑结构中的应用逐渐增多,其中包括不锈钢屋盖结构、不锈钢桥梁、不锈钢墙面等结构中的应用。目前国内对不锈钢力学性能的研究相对较少,其中焊接残余应力是影响不锈钢构件焊接影响的一个重要因素,焊接残余应力的分布规律成为迫切需要研究的内容之一。采用分割条带法对奥氏体不锈钢316(06Cr17Ni12Mo2)包括6种截面的焊接工字型钢的纵向残余应力进行测量,通过对测量数据的分析,得到其残余应力的大小和分布特点,为进一步总结焊接不锈钢构件残余应力的分布和残余应力对不锈钢构件的承载力的影响提供了基础。     

Q690D钢材十字形焊接接头高温后的断裂破坏试验研究

为研究Q690D高强度钢材及焊缝连接件在常温和高温后的断裂性能,选取代表实际梁柱节点局部焊接构造的十字形焊接节点试样,完成了常温和一系列高温后Q690D钢材和ER80-G焊缝金属的单轴拉伸试验,得到了钢材和焊缝金属在不同高温后的弹性模量、屈服强度、极限强度和延伸率。开展了常温和高温后十字形焊接接头的单调拉伸试验和超低周循环试验,研究了Q690D高强度焊接接头的断裂机理,探讨了过火温度、加载制度对焊接接头断裂性能的影响。结果表明:当钢材和焊接接头的过火温度高于600 ℃时,钢材和十字形焊接接头的强度降低,其变形能力开始增大; 800 ℃高温后Q690D钢材的强度降低,但ER80-G焊缝金属的力学性能无明显变化,导致焊接接头经受800 ℃高温后,在单调荷载作用下,其断裂破坏未发生在焊缝处,而发生在母材位置; 循环荷载作用下焊接接头的承载能力和变形能力都低于单调荷载的情况; 试验得到钢材、焊缝金属和焊接接头的力学性能指标,为发展考虑火灾后效应的断裂分析模型提供了基础试验数据。     

N形方主管圆支管相贯节点受力性能试验研究

对10个N形方主管圆支管相贯节点进行了静力性能试验研究。试验节点包括6个内隐蔽部分不焊接的搭接节点、2个内隐蔽部分焊接的搭接节点和2个零间隙节点。分析了节点的受力性能、破坏模式和承载力,并对内隐蔽部分焊接情况、支管轴力性质、节点两侧主管轴压力、支管搭接情况等对节点承载力的影响进行了研究。结果表明：内隐蔽部分焊接与否对被搭接支管受拉的节点承载力影响较大,焊缝断裂是内隐蔽部分未焊接节点常见的破坏模式;在试验几何参数条件下的内隐蔽部分未焊接搭接节点在被搭接支管受压情况下的节点承载力较被搭接支管受拉时大很多;节点两侧主管均有轴压力时的搭接节点承载力较仅一侧主管有轴压力时要小;被搭接支管受拉的搭接节点承载力远远高于相应的零间隙节点。研究表明：国内外现行规范中的N形方主管圆支管搭接节点承载力计算公式对发生主管局部屈曲破坏模式的情况并不适用,而且公式也未考虑内隐蔽部分焊接与否、支管轴力性质和主管轴力等因素的影响,还有待完善。     

钢管贯通焊接球节点的有限元分析

网架(壳)结构中,当杆件的轴力较大、焊接空心球节点承载力不能满足设计要求时,采用钢管贯通焊接球来提高节点的承载力是目前最有效的措施之一。本文采用ANSYS有限元程序,弹塑性应力—应变关系和Von-Mises屈服准则,同时考虑几何非线性的影响,对钢管贯通焊接球节点的极限承载力进行了较为详细的计算分析。本文首先对六组空心球节点进行计算,并与试验结果进行对比来验证本文模型的正确性,进而研究钢管贯通焊接球在单向受力、平面受力和空间受力状态下节点的破坏模式和极限承载力,并比较了不同球壁厚钢管贯通焊接球节点的承载力。本文的分析结果对实际工程设计具有一定的指导意义。     

火灾下焊接空心球节点的温度场分析

基于火灾高温下网格结构的应力特征和火灾性能,按照EuroCode 3和国际标准升温曲线(ISO834 ),对焊接空心球节点火灾高温下的性能进行了非线性有限元数值模拟.研究了焊接空心球节点火灾高温下温度场的分布规律和影响因素.研究结果表明,通过降低焊接空心球节点实际承受的荷载比和外焊钢管的厚度可以有效延长其极限耐火时间,并且焊接空心球节点在受拉时的极限耐火时间比受压时的长.