ZnO陶瓷/金属Cu钎焊接头残余应力计算

采用热弹塑性有限元分析方法,计算了方形ZnO陶瓷与金属Cu钎焊接头中残余应力的大小和分布。发现结果如下:ZnO陶瓷与金属Cu钎焊后会在接头中产生残余应力,其中ZnO陶瓷侧垂直于钎焊界面方向的轴向拉应力是影响ZnO/Cu接头性能的主要因素,轴向拉应力的最大值出现在ZnO陶瓷表面边缘靠近钎焊界面处,当钎料层厚度为0.3 mm时,拉应力在ZnO陶瓷表面边缘距ZnO/钎料层界面0.6 mm处有最大值69.75 MPa。通过钎料层不同厚度的比较计算得出,合适的钎料层厚度能降低ZnO/Cu接头的残余应力,钎料层厚度为0.1 mm时,ZnO陶瓷侧拉应力峰值最小,为30.82 MPa。此外,采用单一缺陷模型计算了钎料层中气孔缺陷的存在对ZnO陶瓷与金属Cu钎焊接头残余应力的影响。计算结果显示,气孔缺陷位于ZnO/钎料层界面时残余拉应力峰值为95.5 MPa,气孔缺陷位于Cu/钎料层界面时残余拉应力峰值为107.2 MPa,拉应力峰值相对无缺陷模型均有大幅升高。     

Q960超高强钢多道焊接头残余应力的数值研究

以Q960超高强钢为研究对象,基于有限元软件,建立热—冶金—力学有限元模型,模拟焊接温度场和残余应力分布.计算结果与接头截面熔池形貌和盲孔法测量的表面应力结果吻合良好,验证了有限元模型的准确性.基于验证模型,讨论和分析了考虑固态相变对Q960超高强钢多道重熔过程中表面及内部应力的分布特征.结果表明:考虑固态相变时,Q960超高强钢单道焊后,焊接接头以拉伸残余应力为主,峰值应力位于热影响区.同时,固态相变效应能够显著降低焊缝中残余应力的大小,以及显著影响横向残余应力的分布.此外,随着焊道数的增加,焊缝中心的横向残余应力呈"阶梯"趋势上升,且在热影响区位置出现局部压应力峰值.     

数值模拟在镁合金焊接接头深冷处理中的应用

利用所建立的有限元模型,对焊接接头进行深冷处理前后的温度场分析,再把模型转化成结构单元进行应力应变场分析。计算结果表明:深冷处理后,受焊接热源影响的焊缝及附近区域横向残余应力和纵向残余应力均增大,距焊缝较远的母材区产生了预压应力;深冷处理后,横向和纵向残余变形均减小。     

焊接钢管高频感应加热的残余应力和组织演变

 随着中国钢铁、冶金与电磁等交叉学科的快速发展,焊接钢管产量及质量日益提升。高频感应加热是生产焊接钢管的核心工序,获取更加精确的焊管高频加热过程的应力分布和微观组织演化规律,是进一步提升焊管品质的关键要素和学者们关切的问题。综合考虑热传导和微观组织转变对应力的影响,针对高频焊管特有的沙漏形热源形貌,定量分析了焊接热影响区微观组织演变过程和残余应力的分布规律,获得了考虑热应力和组织应力的残余应力分布。发现该应力特点为在焊缝附近轴向残余应力较大,最大等效残余应力出现在距焊缝中心1/2壁厚处的热影响区,在壁厚方向管材内部的中间层的残余应力较大,且应力分布与反映高频焊接热源形貌特征的加热温度峰值和加热温度宽度相关。而在焊缝中心处,未考虑组织变化的等效残余应力值是考虑组织变化的1.3倍。掌握焊管高频焊接应力和组织演变的特点和规律,可为优化高频焊接工艺提供理论依据,对提升高频焊管质量具有重要意义。     

LY12铝合金搅拌摩擦焊接头的残余应力研究

搅拌摩擦焊(FSW)具有焊接工艺简单、焊接缺陷少等优点,可用于高强度铝合金的焊接。掌握搅拌摩擦焊接头的残余应力演化规律,对优化焊接工艺,延长工件使用寿命具有重要的研究价值和实际意义。本文采用LY12铝合金搅拌摩擦焊接头为研究对象,通过X射线衍射(XRD)对焊接接头进行残余应力测定。X射线衍射峰位置、强度和宽度变化的实验结果表明:主轴转速和焊接速度一定时,热影响区宏观残余应力大于焊缝区域,两个区域的纵向残余应力都大于横向残余应力,纵向应力和横向应力均以压应力为主,纵向残余应力峰值在热影响区为179 MPa。焊接速度一定时,随主轴转速升高,晶格畸变减小,焊缝区压应力先降低后增加,在热影响区不断增加,焊缝区111取向表现出先增加后减小趋势;主轴转速一定时,随焊接速度增加,晶格畸变加剧,焊缝区宏观残余应力增加,热影响区残余应力减小,焊缝区111取向强度减弱,但仍较200取向严重。     

机械加工对粉末冶金铍材表面残余应力的影响

铍具有低密度、弹性模量高的特性,常用于航天结构件。粉末冶金铍材在机械加工时,表面会产生残余应力,对铍结构件的尺寸稳定性和使用寿命造成直接影响。因此,使用X-ray衍射仪测量铍材表面残余应力,测量了粗车、精车、时效工艺下残余应力沿表面的分布情况;进一步研究了不同机加工艺对铍材表面残余应力影响。结果表明,机械加工时,粉末冶金铍材残余应力均表现为压应力;残余应力与加工线速度负相关,与进刀量正相关,时效处理可有效降低铍材表面残余应力,还能有效提高残余应力的均匀性。     

钛焊管内应力测试

由于钛焊接管是钛带经过滚轧成型过程中经弯曲变形最后焊接而制造出来的,因此管子的外表面有圆周方向的拉应力,内表面有圆周方向的压应力.另外,在焊接过程中,焊缝及其附近区域(热影响区)产生了压缩塑性变形,从而引起焊接残余应力.总之,钛焊管在一定程度上存在着内应力.     

焊接中残余应力的大小与分布及减少措施

熔化焊是通过高温熔化金属以实现连接的一种连接工艺。该焊接过程中金属材料受局部加热，并随之快速冷却，在焊剂与基体金属之间产生了较大的残余应力。其产生大大地降低该焊接结构的抗弯强度，并且容易导致脆性断裂，因此有必要对这种残余应力的大小和分布，以及其受焊接条件影响的规律进行探讨。该文运用ANSYS分析软件，分析了薄板单层电弧焊后残余应力的大小，并且讨论了焊接速度、焊件尺寸大小、焊件外部约束和预热等因素对其大小的影响及其减少的措施。     

浅论GH625合金焊缝的焊后热处理工艺

GH625合金是一种用Cr、Mo固溶强化的镍基合金,采用合适的热处理能促使晶界碳化物析出,在较小范围内可以增加合金的强度.在焊接结构中,热影响区溶合线附近的碳化物溶解和残余应力的恶化作用能使应力腐蚀开裂敏感,存在降低焊件中的残余应力和降低应力腐蚀开裂倾向.降低残余应力常用的方法是焊后热处理,合适的热处理工艺能使晶界碳化物再生,同时焊接残余应力也被降低.     

激光多点冲击Zr基非晶合金残余应力研究

为了实现非晶合金大面积均匀应力强化,采用有限元数值模拟方法研究了激光多点冲击诱导Zr基块体非晶合金的表面残余应力场,得到了不同工艺条件下表面残余应力分布规律。结果表明,经激光冲击强化处理后,非晶合金表面形成了一定深度的残余压应力,然而,残余压应力的大小和均匀性受激光多点冲击工艺参数(相邻光斑中心距、搭接率和冲击波峰值压力)的显著影响;相邻光斑中心距对激光冲击区域的残余压应力影响较小,而光斑之间区域的残余压应力随光斑中心距的减小发生显著变化,其值逐渐增大;相邻光斑搭接冲击时,随搭接率的增加,非晶合金表面形成的残余压应力增大,且均匀性得到提高,搭接率相同时,搭接冲击排数对残余压应力并无明显影响;冲击波峰值压力越大,非晶合金表面残余压应力越大,但应力分布越不均匀,而且冲击区域凹凸不平的微凹坑形貌越明显。     

40CrNiMoA钢同质焊条焊接接头组织和性能研究

分析了焊接电流70A、80A、90A对40CrNiMoA钢焊缝接头组织和力学性能的影响。随着焊接电流的增大,焊缝外观质量较好。随着焊接电流的增大,熔池区温度升高,奥氏体晶粒尺寸增大,导致马氏体组织粗大。焊缝的显微组织为马氏体及少量残余奥氏体。焊缝的硬度远高于母材的硬度,且波动较大。热影响区的硬度从母材向沿焊缝方向逐渐升高。焊接接头纵向应力在焊缝中心为压应力,向外压应力减小。焊接颜色区边界处纵向应力为拉应力,且该点拉应力最大。焊接接头横向应力在焊缝中心为拉应力,向外逐渐增大,焊接颜色区边界处变横向拉应力达到最大。焊接电流和热输入增大,降低了材料的韧性,组织中铁素体增多及焊接残余应力是诱发脆性断裂的原因。焊接电流80A是40CrNiMoA同质焊条平板对接焊接工艺的最佳的焊接电流。     

热处理对GH3128合金接头组织及力学性能的影响

 核能已经逐渐取代化石能源成为新一代能源,作为重要构件的高温气冷堆中间换热器得到了广泛关注。由于GH3128合金具有较好的焊接性、较高的高温抗氧化性能和组织稳定性,有望成为超高温气冷堆中间换热器的候选材料,但基于换热器结构复杂性以及密封性的要求,焊接是其生产和制造的关键成形手段。采用脉冲钨极氩弧焊(GTAW)对GH3128合金2 mm板材进行对接焊,研究了热处理对焊接焊接接头显微组织以及应力的影响。结果表明,在优化焊接工艺参数下,固溶态板材接头表现出最高的强塑性,室温及高温拉伸断裂位置均为母材。由于热轧态与固溶态板材接头热影响区在焊接过程中产生残余应力,导致该区硬化,在高温变形过程中残余应力诱发热影响区μ相析出,对接头持久、蠕变性能造成不利影响。焊后热处理消除了接头热影响区的残余应力,减少了持久、蠕变过程中μ相的析出,接头持久寿命得以改善。在1 200 ℃下,残余应力可为焊后热处理过程中静态再结晶提供激活能,接头热影响区发生再结晶,硬度下降,接头塑性变形能力不协调,导致室温拉伸与950 ℃拉伸断裂位置均为焊接接头。对固溶态板材试样进行不同的焊后热处理,EBSD扫描结果分析发现,接头经过1 100 ℃×10 min热处理后,残余应力明显消失,温度升高至1 140 ℃后,热影响区开始发生再结晶。     

Microstructure and Residual Stress Formation in Induction‐Assisted Laser Welding of the Steel S690QL

Steels of high mechanical strength combined with high toughness, such as those in quenched and tempered condition are required to reduce weight in industrial machinery. Their mechanical performance is impaired by welding operations which often cause a reduction of toughness and increase the probability for cold cracking due to martensite formation in the weld seam. The limited weldability of high‐strength steels therefore demands appropriate joining procedures to increase their use in industrial construction and reduce reworking costs. Induction heating is capable of directly producing heat inside a work piece. This enables the integration of induction heat‐treatments into serial welding processes. In this work, the effect of induction‐assisted laser welding on the microstructure and residual stresses in S690QL butt joints was investigated. The results reveal that conventional laser welding causes strong martensite formation in the weld seam and the heat‐affected zone. This leads to prohibitive hardness values. Induction heat‐treatments result in an efficient reduction of hardness in the fusion zone. However, the efficiency decreases with increasing sheet thicknesses. The residual stress distributions after laser welding with and without induction heating are typical of fusion welding. Although an effective reduction of hardness is achieved by induction‐assisted laser welding, the residual stresses remain significantly high.     

钛基非晶合金电子束焊接热力耦合模拟及非晶化

根据电子束焊接焊缝形貌特征及其深宽比大等特点,选用复合热源作为热源模型.通过线性插值等方式估计材料热力学参数随温度变化,模拟Ti基非晶合金电子束焊接温度场.模拟结果与实际焊缝取得良好的吻合,验证了热源模型的准确性.获得一定变量参数下电子束焊接钛基非晶合金温度场及热循环曲线.在温度场的基础上再进行焊接应力场的模拟,获得残余应力分布曲线.实验验证整个焊件没有晶化相析出,验证了该焊接工艺的可行性.      

Numerical Investigation of Residual Stress in Thick Titanium Alloy Plate Joined with Electron Beam Welding

A finite-element (FE) simulation process integrating three dimensional (3D) with two-dimensional (2D) models is introduced to investigate the residual stress of a thick plate with 50-mm thickness welded by an electron beam. A combined heat source is developed by superimposing a conical volume heat source and a uniform surface heat source to simulate the temperature field of the 2D model with a fine mesh, and then the optimal heat source parameters are employed by the elongated heat source for the 3D simulation without trial simulations. The welding residual stress also is investigated with emphasis on the through-thickness stress for the thick plate. Results show that the agreement between simulation and experiment is good with a reasonable degree of accuracy in respect to the residual stress on the top surface and the weld profile. The through-thickness residual stress of the thick plate induced by electron beam welding is distinctly different from that of the arc welding presented in the references.     

A new finite element model for welding heat sources

A mathematical model for weld heat sources based on a Gaussian distribution of power density in space is presented. In particular a double ellipsoidal geometry is proposed so that the size and shape of the heat source can be easily changed to model both the shallow penetration arc welding processes and the deeper penetration laser and electron beam processes. In addition, it has the versatility and flexibility to handle non-axisymmetric cases such as strip electrodes or dissimilar metal joining. Previous models assumed circular or spherical symmetry. The computations are performed with ASGARD, a nonlinear transient finite element (FEM) heat flow program developed for the thermal stress analysis of welds.* Computed temperature distributions for submerged arc welds in thick workpieces are compared to the measured values reported by Christensen¹ and the FEM calculated values (surface heat source model) of Krutz and Segerlind.² In addition the computed thermal history of deep penetration electron beam welds are compared to measured values reported by Chong.³ The agreement between the computed and measured values is shown to be excellent.     

Simulation of Heat Flow During the Welding of Thin Plates

Based on the finite difference method and the enthalpy model of Shamsundar, a computer model was developed to describe the steady state, two-dimensional heat flow during the welding of thin plates. In order to allow accurate computations of the weld pool configuration, the size of the mushy zone and the temperature distribution near the heat source, a grid mesh of variable spacings was used. The heat of fusion, the size and distribution of the heat source, the temperature dependence of thermal properties, the heat conduction in the welding direction and the surface heat loss during welding were considered. The model was first checked with Rosenthal’s analytical solution of welding heat flow using pure aluminum for examples. Experimental results of 6061 aluminum, including the width of the fusion zone and the thermal cycles at positions in both the fusion and the heat affected zones, were then compared with the calculated results of the heat flow model. The agreement was very good. Finally, in order to demonstrate systematically the quantitative effect of welding parameters such as the heat input, the welding speed and the preheating of the workpiece, a series of computations were made based upon 6061 aluminum.     

Microstructure and mechanical property correlations in AA 6061 aluminium alloy friction stir welds

The influence of friction stir welding on the microstructure development and its role on residual stress distribution in the weldment and mechanical properties has been investigated. The study also focused on the impact of post weld heat treatment on the microstructure and mechanical properties as well as on residual stress distribution. The weld nugget region contained fine equiaxed grains as a result of thermo-mechanical working. Hardness survey showed that nugget region is soft due to precipitates dissolution. Weld joint exhibited lower strength as compared to the parent metal. Post weld Solution Treatment and Aging (STA) of longitudinal welds resulted in strength and ductility equivalent to that of parent metal while transverse weld tensile strength and ductility were lower than that of parent metal even after post weld STA. Residual stress distribution profiles across the weld region are asymmetric with respect to weld centerline, with the largest residual; stress gradients occurring on the advancing side of the weld. Within the region inside the shoulder diameter, residual stress is entirely compressive. Welds exhibited tensile residual stresses in post weld STA condition