Ultrasonic testing on a singly reflected beam using sparse antenna arrays and 3D echo-signal processing

Testing of welded joints in the main shutoff valves (MSVs) of the first circuit of a ВВЭР-440 reactor plant is impeded due to the high structural-noise level and the necessity of using pulses that are singly reflected from the tilted bottom of a branch pipe. Testing on a longitudinal wave leads to the appearance of false reflections, which are formed by pulses at a transverse wave, in the reconstructed image. Since the amplitude of false reflections can be commensurable with the amplitude of reflections that were obtained at longitudinal waves, the analysis of such images may be hampered. To increase the quality of an image, it is proposed to record echo signals using sparse antenna arrays and use 3D processing of echo signals. Numerical and model experiments showed that this approach increases the frontal resolution in the additional plane by several times and reduces the amplitude of false reflections, thus making it possible to increase the sensitivity and reliability of expert ultrasonic testing of the principal shutoff valve.     

低碳钢焊缝金属强度组配对焊接残余应力分布的影响规律

采用热弹塑性有限元方法,对平板对接接头中焊缝金属强度组配对焊接残余应力分布的影响进行了研究。结果表明,对于高组配接头,纵向残余应力的峰值接近焊缝金属的屈服极限,出现在焊缝中心。对于低组配接头,纵向残余应力的峰值接近母材的屈服极限,并发生在焊缝附近。随着对含有残余应力的接头施加外载,焊缝金属强度组配对纵向应力分布的影响依然存在,但残余应力的影响在减小。对承受外载的焊接接头,逐步卸除外载后,焊缝横截面     

力学不均匀性对含横向裂纹焊接接头J积分的影响

采用 MARC有限元程序提供的 Delorenzi虚拟裂纹扩展方法计算了平面应力条件下不同强度匹配的焊缝纵向受载的含横向裂纹的焊接接头在不同载荷的广义 J积分。计算结果表明 :力学不均匀性对含横向裂纹焊接接头的 J积分有重要影响 ,低匹配焊接接头中积分路径穿越焊缝与母材界面的 J积分值高于积分路径在焊缝内的 J积分值 ,高匹配焊接接头中积分路径穿越焊缝与母材界面的 J积分值低于积分路径在焊缝内的 J积分值 ;载荷越大 ,焊缝与母材的强度差别越大 ;积分路径中包含的焊缝与母材界面长度越大 ,J积分的差值越大。力学不均匀性对焊缝纵向受载的含横向裂纹的焊接接头 J积分的影响是由焊缝与母材的强度差别及积分路径中包含的焊缝与母材界面长度的不同造成的     

Directivity analysis of ultrasonic waves on surface defects using a visualization method

Ultrasonic testing uses the directivity of the ultrasonic wave, which propagates in one direction. The directivity is expressed as the relationship between the propagation direction and its sound pressure. The directivity of an ultrasonic wave is related to the choice of probe arrangement, testing sensitivity and scanning pitch, and correct measurement of defect size and location. This paper investigated the directivity of ultrasonic waves, which are scattered from a slit defect located in simulated butt weld joint using a visualization method. When the defect size was smaller than the wavelengths, clear directivity in the reflected wave was observed. When the ratio of defect size to wavelength is greater than 1.5, measured directivities almost agree with the theoretical directivity. The directivity of shear waves scattered from the slit defect varied according to probe direction (Far defect, Near defect). The angle of reflection wave became similar to angle of incidence as the height of excess metal in welded joint increased.     

CO2 laser welding of zinc-coated steel sheets

Welding of zinc-coated steel sheets for the automotive industry has been investigated experimentally and theoretically, using a continuous wave 2 kW CO₂ laser. The specimens of 0.8, 1.0 and 1.2 mm thickness were welded as butt joint and lap joint. Argon gas was shielded co-axially to reduce the plasma and to protect the molten, pool from atmosphere. The mechanical tests of specimens were carried out to investigate the ductility of welds in butt joint and lap joint, using the Erichsen test, ball punch test and tensile shear test. The value of transverse weld pattern is higher than others. The fatigue life of longitudinal weld is superior, but that of circular weld pattern is inferior due to the high tensile residual stresses in the weld. The maximum Erichsen value was obtained as 96% and the deformability of zinc coated steel butt-welded was found to be 80% in the ball punch test. The high pressure formed by vaporization of zinc with the low boiling temperature during laser lap-joint welding splattered the molten pool and created porosities in the weld. The optimum gap was calculated to be 0.1 mm in the lap joint welding of zinc-coated steel sheet which was a good agreement with the experimental result.     

Ultrasonic control of welded joints in a Du800-type pipeline. Part I: Restoring reflector images by digital focusing with an antenna

The reliability of ultrasonic nondestructive testing can be improved by acquiring reflector images that can be used to solve the defectometry problem, that is, to determine the type, size, and coordinates of a reflector deep in the sample. Welded pipelines with a diameter of 840 mm (Du800 type) are used at nuclear power facilities in Russia; ultrasonic testing of these pipelines is thus a topical problem. In model experiments, echo signals were registered by two antenna arrays, situated on the opposite sides of a welded joint (the N- and P-sides). The arrays performed scanning along and across the welded joint. The following techniques were used to reconstruct reflector images by the DFA method in a homogeneous isotropic medium: registering echo signals for all emission–reception combinations of elements in the two antenna arrays with the aim of merging partial images into a single image by different methods; reconstructing images on different acoustic schemes with allowance for wave-type transformation; and registering echo signals in a triple-scanning mode with subsequent coherent summation of partial images. It has been shown that the above techniques are insufficient for producing high-quality images.     

镁合金激光胶接焊接头微观及力学性能

采用激光胶接焊焊接镁舍金，利用现代测试手段分析接头的微观组织特征，并分别研究激光焊、胶接和激光胶接焊3种接头在相同工艺参数下的剪切力和抗剥离力，在较好的工艺参数下，激光胶接焊焊缝成形良好。在激光热源的作用下，焊缝区内胶层受热分解并以气体形式逸出焊缝，并未影响焊缝的组织熔舍；焊缝边缘附近胶层炭化裂解，存在胶层失效区，虽减小胶层的承载面积，但该区域很窄，对接头的实际承载能力影响不大。激光胶接焊接头剪切力最大，胶接接头次之，激光焊接接头剪切力最小；激光胶接焊接头的抗剥离力远大于胶接接头的抗剥离力。激光胶接焊有效提高接头的实际承载能力，因此具有很大的发展潜力。     

Wave transmission at discontinuities using wavenumber-frequency techniques

The problem of wave transmission between two finite beams joined by a cross beam welded between them is solved taking full account of longitudinal and flexural waves in all the beams. Prediction of longitudinal and flexural wave transmission through the “T” joints in the beam system was performed over a wide band frequency range. The wavenumber-frequency spectrum was used to separate the wave types based on their different dispersive characteristics. Flexural direction forces at one end of the beam system were examined. The experimental data were taken using an accelerometer array and a simultaneous twenty-three channel measuring system. A transfer function correction technique was employed to account for the instrumentation errors. Experimental results were confirmed by the finite element analysis results. The total mean squared vibrational energy levels were calculated in each section of the beam system to quantify the transmission characteristics of both flexural and longitudinal waves passing through the beam joints.     

含裂纹强度失配焊接接头弹塑性变形分析

采用有限元方法对平面应变条件下含裂纹不同强度失配的平板拉伸焊接接头的弹塑性变形进行了分析,研究了焊缝与母材强度失配系数、焊缝硬化性能、裂纹长度等对接头塑性变形的影响。结果表明：强度失配系数对接头塑性变形有显著影响。低匹配时,变形首先集中在焊缝中,而高匹配则对焊缝起到了一定的保护作用。失配系数一定时,不同焊缝硬化性能接头的塑性变形发展趋势是一致的;但当外载较大时,局部塑性变形程度不同,焊缝的硬化性能降低,裂尖塑性变形增大。
     

Effect of post weld aging treatment on tensile properties of electron beam welded AA2219 aluminum alloy

Aluminum alloy 2219 (Al-6.5%Cu) is a favourite age hardenable alloy for aerospace applications because of its excellent welding characteristics. Though AA2219 has got an edge over its 6000 and 7000 series counterparts in terms of weldability, it also suffers from poor joint strength when welded. In this investigation an attempt has been made to improve the welded joint strength through post weld aging treatment. This paper presents the effect of post-weld aging treatment on tensile properties of electron beam welded AA2219 aluminum alloy. Square butt joints were fabricated using an electron beam welding (EBW) machine of 100 kV capacity. The joints were given post-weld artificial aging treatment. Tensile tests were carried out using 100 kN, electro-mechanical controlled universal testing machine. It is found that the post-weld aging treatment is beneficial for improving weld metal hardness and tensile properties. This is mainly due to the uniform distribution of CuAl₂ precipitates in the weld metal region in post-weld aged joints compared to as welded joints as evident from weld metal microstructure.     

Ultrasonic Scattered Field Distribution of One and Two Cylindrical Solids with Phased Array Technique

The scattered fields of plane waves in a solid from a cylinder or sphere are critical in determining its acoustic characteristics as well as in engineering applications. This paper investigates the scattered field distributions of different incident waves created by elastic cylinders embedded in an elastic isotropic medium. Scattered waves, including longitudinal and transverse waves both inside and outside the cylinder, are described with specific modalities under an incident plane wave. A model with a scatterer embedded in a structural steel matrix and filled with aluminum is developed for comparison with the theoretical solution. The frequency of the plane wave ranged from 235 kHz to 2348 kHz, which corresponds to scaling factors from 0.5 to 5. Scattered field distributions in matrix materials blocked by an elastic cylindrical solid have been obtained by simulation or calculated using existing parameters. The simulation results are in good agreement with the theoretical solution, which supports the correctness of the simulation analysis. Furthermore, ultrasonic phased arrays are used to study scattered fields by changing the characteristics of the incident wave. On this foundation, a partial preliminary study of the scattered field distribution of double cylinders in a solid has been carried out, and the scattered field distribution at a given distance has been found to exhibit particular behaviors at different moments. Further studies on directivities and scattered fields are expected to improve the quantification of scattered images in isotropic solid materials by the phased array technique.     

面能量对激光—电弧复合焊接焊缝及熔滴过渡的影响

引入面能量的定义,从激光功率、电弧参数和焊接速度等方面来研究面能量的变化对焊缝熔深、熔宽、焊缝成形系数和熔滴过渡的影响,试图建立激光能量与电弧能量之间的最佳配比关系以及面能量与熔深的定量关系。采用高速摄像系统观测熔滴过渡模式和等离子体形态的变化,并采集焊接过程中的电弧和熔滴图像;利用激光共聚焦显微镜观察焊缝形貌,并测量焊缝熔宽、熔深等数据。试验研究发现:激光与电弧两热源之间存在最优匹配范围;电弧电压与焊接电流之间存在U(15 1)0.05I的关系式;焊接速度的降低与焊缝熔深的增加并非线性关系,可选择的焊接速度是一个区间,该区间内存在一个最佳的焊接速度,并对应一个最佳的面能量。因此,在具体的激光—电弧复合焊接中,需要根据板厚、接头形式等确定激光与电弧的能量参数,选择合适的面能量。     

不同强韧性组配的16Mn钢焊接接头的断裂性能和裂行为

对16Mn钢不同组配焊接接头的断裂性能和断裂行为进行了试验研究。认为在高应力塑性断裂和高应力脆性断裂状态下,16Mn钢接头的断裂强度为焊缝强度和接头各部分塑性变形能力所决定,提高焊缝强度以及提高焊缝和母材的塑性均有利于提高接头的抗断裂能力;在低应力脆性断裂状态下,接头的抗断裂性能是可以根据焊缝的低温冲击韧度进行评价的。焊接接头各部分塑性变形能力及其相互关系对焊接接头的断裂行为具有不可忽视的影响,是评价接头断裂性能的重要依据。     

深窄间隙焊接技术在大厚度构件材料焊接中的应用研究

窄间隙焊接技术作为一种高效焊接方法以其大大降低熔敷量和节约制造时间的优点,使其在大厚度构件制造中具有广阔的应用前景,但是焊接过程的稳定性及侧壁熔合等缺陷的存在,成为影响构件高品质制造的关键问题。利用深窄间隙埋弧焊接方法成功制造了外径尺寸为2 500 mm,厚度达150 mm的转子模拟件,采用多层双道焊接方法,实现了良好的侧壁熔合效果,且未发现夹杂等缺陷,表面该焊接接头具有较高的成形质量。基于该焊接接头开展冲击韧度、拉伸等力学性能试验,表明该接头的力学性能完全满足使用需求。从而验证了深窄间隙焊接技术在大厚度核电转子焊接中应用的可靠性。     

Predictions of the optimized friction stir welding process parameters for joining AA7075-T6 aluminum alloy using preheating system

The scope of this investigation is to evaluate the effect of welding parameters on the mechanical properties and microstructural features of 3-mm-thick AA7075-T6 aluminum alloy subjected to gas heating system as a preheating source during friction stir welding. Toward this end, a gas heating system was designed to heat up the weld seam just ahead of rotating tool to soften the material before being stirred. Three welding parameters, five levels, and a central composite design (CCD) have been used to minimize the number of experimental conditions. The joining parameters such as tool rotational speed, welding speed, and shoulder diameter have a significant influence on determining the mechanical properties of the welded joints. It was found that using preheating system mostly can result in higher total heat input into the weld joint and effectively reduces the formation of defects when unsuitable process parameters were used. Also, an attempt has been made to establish the mathematical model to predict the tensile strength and microhardness of the joints. The optimal welding conditions to maximize the final responses were investigated and reported. The results show that the joint fabricated at a rotational speed of 1,050 rpm, welding speed of 100 mm/min, and shoulder diameter of 14 mm exhibited higher mechanical properties compared to other joints.     

Determining the distance between antenna arrays and the speed of longitudinal waves in a test object when reconstructing the profile image of the bottom of a weld in ultrasonic testing

A method is considered for determining the distance between two wedges and the speed of longitudinal ultrasonic waves in a test object when measuring the profile of the surface of pipelines under the bead of a weld. The method makes it possible to reduce the error in determining the profile of the bottom of a pipeline in the course of testing by refining the distance between the wedges and the speed of sound using head-wave pulses. Results of numerical experiments are provided for the processing of echo signals calculated by the finite-difference method in the time domain. The efficiency of the proposed technique is demonstrated with some model experiments.     

Research on corrosion behavior of A6N01S-T5 aluminum alloy welded joint for high-speed trains

For high speed trains, safety is of utmost importance. Salt fog corrosion, intergranular corrosion tests were employed to observe the corrosion behavior of welded joint of A6N01S-T5 aluminum alloy of high-speed trains. Tensile strength and hardness changed after corrosion was tested. The micro morphologies were observed by metalloscope and laser confocal scanning microscope (LCSM). The corrosion loss and corrosion loss ratio were also investigated. The results showed that the heat affected zone (HAZ) was the most sensitive to corrosion in welded joint in the salt fog corrosion test. The potential of the corrosion of the intermetallic compound on the surface was different from the Al matrix potential, which easily generated corrosion micro-batteries that generated the corrosion pit. The weld zone was the most sensitive to corrosion in the welded joint in the intergranular corrosion test, because much corrosion produced an intermetallic phase such as CuAl₂, MgZn₂, Mg₅Al₈, which formed the deficient Cu or Mg zone potential. The potential is low, which acted as an anode and corroded. The residual stress test on the weld of the A6N01S-T5 of the W1 of the exterior surface of roof of high speed train showed there was distributed high tensile stress and compressed stress in the weld zone, HAZ zone and matrix zone. The defects will spread under the high stress and make the corrosion become severe.     

水工钢结构焊接残余应力有限元模拟分析

采用有限元数值计算方法模拟了钢结构在焊接过程中产生的残余应力和变形特性,采用了双线性弹性-塑性模型、Von Mises屈服准则,和增量原理处理焊接过程中的材料非线性问题,建立了热-结构耦合有限元模型和方法。数值仿真结果表明,采用单元生死处理方法对于模拟多道焊缝问题是有效的。     

Influence of axial magnetic field on shape and microstructure of stainless steel laser welding joint

The morphology and microstructure of the weld joint have significant influence on mechanical properties of welded specimens. In this paper, the mechanism on how the external magnetic field affected weld profile and microstructure was discussed by applying the longitudinal steady magnetic field to laser welding for SUS301 stainless steel. The optimal and scanning electron microscopes were used to measure the shape of the cross section and observe the microstructure after welding. The results showed that the shape of the cross section and microstructure could be significantly changed using the external magnetic field. Moreover, joint shape changed distinctly with the magnetic field intensity changing. With the increasing of magnetic flux density, the weld profile of the full penetration model changed from funnel to X type; meanwhile, the bottom weld width increased by 40%. In addition, the partial fusion zone occurred, and the weld width decreased by 20% while penetration increased by 18% when magnetic flux density turned into 380 mT. As far as microstructure of weld joint was concerned, it appeared that application of axial magnetic field led to indistinct fusion line and blocky austenite in big size rather than columnar grain in the center of the cross section. This phenomenon could be explained by numerical simulation results.     

某发动机动力涡轮轴承座氩弧焊工艺研究

动力涡轮轴承座是某航空发动机的重要部件,在对其上的各种安装座氩弧焊后出现了焊接裂纹,严重影响了产品质量和交付进度.本文通过荧光检查和冶金分析,确定了氩弧焊焊接裂纹的性质为结晶裂纹,并针对结晶裂纹的产生机理和预防措施,调整了焊接参数.试验验证表明,采用增设焊接接头坡口、采用分段式焊接、改进焊缝收弧方式以及控制焊接速度等工艺措施,能够有效地防止结晶裂纹的产生,提高产品的质量.