焊接微缺陷磁光成像检测有限元分析

目的 研究铁磁材料焊接微缺陷的磁光成像规律.方法 运用漏磁检测原理和法拉第磁致旋光效应,建立微缺陷三维有限元模型,分析微缺陷磁光成像过程与磁场之间的关联,研究不同提离值、励磁电流、缺陷宽度、缺陷深度下的磁光成像,以及探索这些因素对磁光图像特征的影响.在此基础上,对最小宽度为0.05 mm的微缺陷进行磁光成像检测实验,并...     

1 000 MPa级高强钢焊接件的氢脆敏感性研究

利用氢渗透试验、慢应变速率拉伸试验(SSRT)研究了1 000MPa级高强钢(HSS)焊接件在海水中的氢渗透行为及其应力腐蚀敏感性,结合SEM观察了试样的断口特征,并利用电化学试验和显微组织观察分析了焊接件不同区域的氢脆特征。结果表明:相对于焊缝区(WM)和母材区(BM),热影响区(HAZ)的自腐蚀电位最负、析氢电位最正,更容易发生腐蚀和析氢行为。热影响区的氢扩散系数最大,具有较强的吸氢倾向。动态电化学充氢对高强钢焊接件的影响主要体现在对塑性的损减方面;随着极化电位的负移,高强钢焊接件的强度没有明显变化,但断面收缩率、断后延伸率均减小,断裂方式逐渐由韧性断裂变为解理断裂;当极化电位约为-930mV(vs SCE)时,高强钢焊接件的氢脆系数达25%;在不同充氢极化电位下,焊接件试样的断裂位置多在热影响区。     

Real‐Time Analysis of Magnetic Hyperthermia Experiments on Living Cells under a Confocal Microscope

Combining high‐frequency alternating magnetic fields (AMF) and magnetic nanoparticles (MNPs) is an efficient way to induce biological responses through several approaches: magnetic hyperthermia, drug release, controls of gene expression and neurons, or activation of chemical reactions. So far, these experiments cannot be analyzed in real‐time during the AMF application. A miniaturized electromagnet fitting under a confocal microscope is built, which produces an AMF of frequency and amplitude similar to the ones used in magnetic hyperthermia. AMF application induces massive damages to tumoral cells having incorporated nanoparticles into their lysosomes without affecting the others. Using this setup, real‐time analyses of molecular events occurring during AMF application are performed. Lysosome membrane permeabilization and reactive oxygen species production are detected after only 30 min of AMF application, demonstrating they occur at an early stage in the cascade of events leading eventually to cell death. Additionally, lysosomes self‐assembling into needle‐shaped organization under the influence of AMF is observed in real‐time. This experimental approach will permit to get a deeper insight into the physical, molecular, and biological process occurring in several innovative techniques used in nanomedecine based on the combined use of MNPs and high‐frequency magnetic fields.     

A Comparative Study of Different Segmentation Techniques for Detection of Flaws in NDE Weld Images

For detecting the flaws and their type in radiographic images (having different types of flaws), three segmentation techniques have been applied here. Every segmentation technique has its own advantages and disadvantages i.e. results obtained are of varying quality. Taking this into account, comparative study has been performed here to find the best segmentation technique for a particular type of flaw. These methodologies are compared and concluded to be effective for all possible nine types of weld flaws detection (Slag Inclusion, Worm Hole, Porosity Incomplete penetration, Under cuts, Cracks, Lack of fusion, Weaving fault Slag line), and feature extraction, after being successfully tested on more than 80 radiographic images obtained from EURECTEST, International scientific Association Brussels, Belgium, and 24 radiographs of ship weld provided by Technic Control Co. (Poland) were used, obtained from Ioannis Valavanis Greece, and 67 radiographs of actual weld test samples obtained from Bharat Heavy Electrical Limited (BHEL) India. The comparison with other NDT methods with application of image processing on the radiographic images of weld defects is aimed to detect the defects reliably and make accept/reject decision as per the international standard.     

A Parametric Study of Magneto-Optic Imaging Using Finite-Element Analysis Applied to Aircraft Rivet Site Inspection

Magneto-optic/eddy current imaging (MOI) has become increasingly popular for inspecting aging aluminum airframes for cracks and corrosion due to its accuracy, reliability, and ease of use. As inspection requirements change, modifications to the MOI system must be made to improve sensitivity and resolution to reliably detect smaller and/or deeper defects in the aircraft structure. Incorporating such improvements by "cut and try" methods is time-consuming and expensive. Therefore, a numerical simulation model that produces quantitative values of the magnetic fields associated with induced eddy currents interacting with structural defects is an essential complement to the instrument development process. Such a model provides a convenient tool for parametrically evaluating the effectiveness of the MOI for detecting various structural defects. This paper presents a three-dimensional finite-element model of Maxwell's equations, utilizing the A-V formulation for numerical simulation of the MOI operation. The model is used to predict quantitative values of field distributions that produce the binary magneto-optic images of subsurface fatigue cracks at rivet sites in an aluminum airframe structure. A parametric study is performed to determine the effects of MOI operational parameters on the binary images. A skewness parameter based on the binary images is established to provide a measure of defect size. This parameter will prove useful for automatic detection and classification of defects. The model-generated images show good agreement with experimentally derived MOI images     

Fatigue characteristics of pulsed MIG-welded Al-Zn-Mg alloy

Pulse-current MIG welding of Al-Zn-Mg alloy was carried out using an extruded section of base material and Al-Mg (5183) filler wire. During welding the pulse parameters such as the mean current and pulse frequency were varied and their effect on the geometry and porosity content of weld deposit as well as the fatigue life of the weldment was studied. The pulse parameters were found to affect significantly the geometry and porosity content of weld deposit and consequently the fatigue life of the weldment. For a comparative study, weldments were also prepared by using conventional continuous current MIG-welding process, where welding currents equivalent to the mean currents of pulsed process were used. The fatigue life of the weldment was correlated with the geometry and porosity content of weld deposit.     

Preparation and characterization of temperature-responsive magnetic composite particles for multi-modal cancer therapy

The temperature-responsive magnetic composite particles were synthesized by emulsion-free polymerization of N-isopropylacrylamide (NIPAAm) and acrylamide (Am) in the presence of oleic acid-modified Fe₃O₄ nanoparticles. The magnetic properties and heat generation ability of the composite particles were characterized. Furthermore, temperature and alternating magnetic field (AMF) triggered drug release behaviors of vitamin B₁₂-loaded composite particles were also examined. It was found that composite particles enabled drug release to be controlled through temperature changes in the neighborhood of lower critical solution temperature. Continuous application of AMF resulted in an accelerated release of the loaded drug. On the other hand, intermittent AMF application to the composite particles resulted in an “on–off”, stepwise release pattern. Longer release duration and larger overall release could be achieved by intermittent application of AMF as compared to continuous magnetic field. Such composite particles may be used for magnetic drug targeting followed by simultaneous hyperthermia and drug release.     

Failure Investigation of a Defective Weldment of an Oil Product Transmission Pipeline

An API 5L X52 oil product transmission pipeline experienced a sudden failure at a portion which had been buried in the bed of a river crossing after 33 years of service. Results showed that mechanical properties of the weldment had been reduced due to weld defects. The defects had been formed during construction welding and installation of the pipeline in the bed of the river crossing. No failure had occurred until this portion of the buried pipeline came out of its place in the bed of the river crossing. Under this condition, defective weldment (due to hydrogen stepwise cracking, incomplete fusion, porosity formation, and entrapped slag inclusion) was not capable of enduring stress imposed by the strong river stream and consequently failed. Metallographic and SEM studies as well as stress analysis were used for pipeline fracture investigation.     

Magnetic behavior in an ordered Co nanorod array

The magnetization reversal process of an ordered Co nanorod array is shown using the images obtained from successive in-field magnetic force microscope (MFM) measurements. The magnetization reversal model is discussed according to local and whole magnetization reversal properties measured by the polar magneto-optical Kerr effect (PMOKE) and an alternating gradient magnetometer (AGM), respectively. Additionally, the dipolar field was probed using in-field MFM measurements. By removing the effect of the dipolar field, an intrinsic switching field distribution (SFD) is shown in a map with a hexagonal array. A detailed study of the dipolar field in ordered nanorod arrays with various diameters and pitches was carried out by numerical calculations.     

Improving the fatigue performance of fillet weld terminations

A specially designed stress-concentration-reducing part was incorporated in the wrap-around welds at the ends of fillet-welded longitudinal attachments, that is, at fillet weld terminations − ubiquitous weld details having a notoriously poor fatigue resistance. The incorporation of this part at the terminations of the fillet-welds substantially decreased the weld toe stresses in those locations where fatigue cracks customarily start, reduced weld toe residual stresses and promoted increases in the weld-toe notch-root radius. In the long-life regime, the incorporation of these small, added parts increased weldment fatigue life by 300% and fatigue strength by 30%. It was found that the full benefit of the added part could only be achieved when welding processes were employed that avoided the production of cold-lap weld-toe defects.     

Influence of Heterogeneous Magnetism on Magneto-Optical Properties

The influence of inhomogeneity on magnetic materials is considered; in particular, we examine how it affects the magneto-optical (MO) response of films and multilayers. From ab initio calculations of the band structure, the optical conductivity tensor is derived, providing the basis for computing the MO spectra. The presence of magnetic nanoprecipitates is taken into account by modeling the system as an effective medium or as an infinitely thin layered structure. A possible depth concentration distribution of the magnetic species is also accounted for, by considering the structure as a sequence of layers. This formalism is applied to some real systems constituted by magnetic particles dispersed in a hosting nonmagnetic matrix. The agreement between theoretical and measured MO Kerr effect spectra supports the validity of the model and establishes its predictive power, suggesting that the analysis of experimental MO spectra can provide information not only on the magnetic, but also on the structural properties of heterogeneous magnetic systems.     

Macromechanics study of stable fatigue crack growth in Al–Cu–Li–Mg–Ag alloy

This study was made on a fresh variety of Al–Li base alloy to investigate the role of ageing precipitates and microstructure dimensions in the fatigue crack growth resistance. The fatigue crack growth rate was measured in three different states of the material (i.e. base metal in T8 condition, friction stir weld and laser beam weld in full‐aged condition). Metallurgical analysis showed that the base metal in T8 temper is precipitation hardened by an equivalent amount of δ′ (AL₃Li), T₁ (AI₂CuLi) and θ′ (AI₂Cu) precipitates. The friction stir weld retained the morphology of strengthening precipitate; however, coarsening of Cu containing precipitates has occurred. On the other hand, laser beam weld showed a different type of CuAl phase morphology, which is characteristic of cast metal. The results of fatigue tests confirmed that fatigue crack growth resistance largely depends on microstructural features, specifically the strengthening phases. The fatigue crack resistance was in the order of base metal > laser beam weldment > friction stir weldment. The CuAl phase played a vital role in the crack closure of the laser beam weldment, thus enhancing the fatigue life as compared with the friction stir weldment, which was evident from the plot between log of da/dN (crack growth in each cycle) and log of ΔK (stress intensity range).     

Creep stress concentrations in mis-matched weldments—starting points for early creep damage and creep cracking

The material creep properties of weldments, i.e. the minimum creep strain rate, the creep rupture strength and the creep ductility, do in general differ from those of the parent material. It is often assumed that if the weld material creep strength is higher than that of the parent, the life of the weldment will also be higher. This is not always true. In fact, when subjected to a prescribed displacement, e.g. a circumferential weldment in a pipe subjected to internal pressure, a creep hard weld develops a stress concentration which may result in a reduced life expectancy of the weldment system. Similarly, the properties of the heat affected zone often differ from those of the parent and weld material properties which may be one reason for early Type IV cracking. In addition, the weld preparation geometry, the width of the HAZ and other geometric parameters influence the stress distribution. The present paper summarizes some of the effects of material property variations in weldments and their impact on the creep life expectancy. It is shown that the stress concentrations resulting from material property mis-matching may be high enough to produce premature creep damage in the weldment, or will cause creep cracking starting from initial defects.     

Mixed magnetooptical contrast induced by an inhomogeneous magnetic field in metal films with planar anisotropy

Magnetooptical (MO) images induced by a strongly inhomogeneous external magnetic field in magnetic metal films with planar anisotropy have been studied. In the polar Kerr effect geometry, MO images created by the normal magnetization component is observed. In the meridional Kerr effect geometry, a superposition of the MO images (mixed MO contrast) is observed, which is determined by the distribution of the normal and horizontal magnetization components. Calculation of distribution of magnetization in a film is carried out, a field of magnetic system corresponding to coordinate dependence and are simulated corresponding MO images and the corresponding MO images have been simulated, which demonstrate satisfactory agreement between the theory and experiment.     

Investigation of metallurgical and mechanical properties of 21st century nickel-based superalloy 686 by electron beam welding technique

Electron Beam Welding (EBW) was performed on the highly corrosion resistance superalloy 686. The present research work investigates the metallurgical and mechanical properties of the weld joint fabricated by Electron Beam Welding technique, and the results are compared with the base metal. Optical and Scanning Electron Microscope (SEM) analysis were carried out to study the structural properties of the weld joint. The fine equiaxed dendritic structure was revealed in the Center Fusion Zone (CFZ). The columnar dendrite was noticed in the Transition Fusion Zone (TFZ). Energy-dispersive X-ray spectroscopy (EDS) analysis results show that segregation of Mo and W were noticed in the sub-grain boundary. X-ray diffraction analysis (XRD) confirmed the presence of Mo and W rich phases in the weldment. Tensile testing was carried out to evaluate the strength and ductility of the weld joint. The result revealed that the weld strength was equal to the base metal strength. The presence of Mo and W-rich intermetallic phase reduced the ductility and toughness of the weld joint compared to base metal. Bend test confirmed the defect-free weld joint that was achieved in the Electron Beam Welding technique. The corrosion rate of base metal and EBW weldment are calculated in the synthetic seawater environment with the help of Potentiodynamic polarization experiment, and corrosion rate is measured with Tafel’s interpolation technique. The corrosion test result shows that the resistance of EBW weldment is lesser than base metal corrosion resistance because of the microsegregation of alloying elements in the interdendritic region.     

Effect of heat input and weld chemistry on mechanical and microstructural aspects of double side welded austenitic stainless steel 321 grade using tungsten inert gas arc welding process

Stainless steel 321 is a stabilized austenitic grade that prevents the formation of chromium carbides at the grain boundaries and subsequently reduces the risk of corrosion attack at the weld surface by forming titanium carbide. It is primarily used in industries such as pressure vessels, boilers, nuclear reactors, carburetors and car exhaust systems. In order to assess the effect of gas tungsten arc welding process parameters on weld penetration, the proposed Taguchi L₉ orthogonal matrix has been selected with two factors and three levels for welding austenitic stainless steel 321 by adjusting the welding current and welding speed. Bead-on-plate experiments were performed on base metal of 6 mm thick plate by changing the process parameters, and corresponding weld bead measurement and macrostructure images are examined. Maximum depth of penetration −3.3017 mm is achieved with a heat input −1.4058 kJ/mm, i. e., welding current-220 A and welding speed-120 mm/min. Double-side arc welding technique is used to obtain full penetration on 6 mm thick plate. The quality of the weldment was assessed using non-destructive radiography inspection. Mechanical integrity and microstructural characteristics of the weldments were studied using tensile (transverse and longitudinal), bend, impact, microhardness, optical microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction analysis, ferrite number measurement and scanning electron microscope. The results reveal that the double side-tungsten inert gas weldment have better mechanical properties. It is corroborated from the weld metal microstructure that it contains γ-austenite, δ-ferrite and titanium carbides (intermetallic compounds). X-ray diffraction analysis and energy dispersive x-ray spectroscopy plots confirm the increase in the ferrite phase in weld metal. The ferrite measurement results show that the ferrite volume in the base metal and weld metal is 1.2 percent and 6.1 percent respectively. In addition, the higher δ-ferrite volume in the weldment helps in attaining superior mechanical integrity. Fractography shows that the failure mode of the weld metal and the base metal is ductile.     

Q550D高强钢焊接节点疲劳强度试验研究

试验研究了国产Q550D高强度结构钢、焊缝的基本力学性能以及横向对接焊缝和非承载横向角焊缝连接件的疲劳性能。介绍了试件的加工方法、焊接工艺、疲劳试验及其数据处理方法,将疲劳试验结果与国内外钢结构设计规范以及他人的研究结果进行了分析对比。研究表明：Q550D高强钢母材及其焊缝具有优良的延伸率和低温冲击韧性,余高磨平的钢板对接焊缝和横向角焊缝连接件的疲劳强度都分别显著地高于国内外钢结构设计规范关于普通强度钢材相应焊接节点的疲劳强度,200万次疲劳强度分别提高了72%~125%和27%~68%。钢板对接焊缝的余高磨平可改善因焊缝的几何形状和缺陷引起的应力集中程度,比原状焊缝具有好的疲劳性能。无论余高磨平或未磨平的钢板对接焊缝,还是横向角焊缝连接件,它们都具有随高强钢屈服强度的增加而疲劳强度提高的趋势。分别提出了Q550高强钢钢余高磨平的钢板对接焊缝和横向角焊缝连接件的S-N曲线,可供抗疲劳设计参考。     

Creep resistance of similar and dissimilar weld joints of P91 steel

Abstract

Two experimental weld joints, a similar weld joint of 9Cr–1Mo steel and a dissimilar weld joint of 9Cr–1Mo and 2.25Cr–1Mo steels, were fabricated by the TIG+E method and post-weld heating was applied. Creep testing was carried out at temperatures ranging from 525 to 625°C in the stress range 40–240 MPa. Creep rupture strength was evaluated using the Larson–Miller parameter. Extended metallography including transmission electron microscopy was performed and critical zones were indicated where fractures were concentrated during the creep exposure. At high temperatures rupture of the dissimilar weldment occurred in the heat affected zone (HAZ) of the weld metal while rupture of the similar weldment was located in the HAZ of the parent material. The processes of recovery seem to be the main causes of decrease in creep rupture strength of both weld joints in comparison to the parent materials.     

Defect characterisation in Austenitic stainless steel plate weld by multimulti frequency Eddy current testing technique

Multi multi frequency eddy current testing method has been a novel technique for defect characterisation and classification. In this technique any particular type of defect in a component can be detected in the presence of different type of other defects. In the present investigation attempts have been made to detect cracks in the interfaces between a weld pool and the bulk material in a thick austenitic stainless steel plate using this technique. The eddy current signals from the weld pool (having different magnetic permeability and electrical resistivity from the bulk) and the “lift off” of the eddy current sensor have been successfully suppressed by judicious choice of the experimental parameters and utilizing a software ‘mix algorithm’. This technique can be very effectively used as an NDT tool for a ‘Go/No Go’ test for any particular type of defect in components of mass production.     

Polarization dependence of readout signals from periodic one-dimensional arrays of magnetic domains in magneto-optical media and crystalline-amorphous line pairs in phase-change media of optical recording

Polarization dependence of signals from periodic one-dimensional arrays of magnetic domains in magneto-optical (MO) media and crystalline domains in amorphous phase-change (PC) media has been studied by theoretical calculation and experiment. The MO signal in the small-period regime depends on the direction of incident polarization. The relative strength of the E(?) and E(?) signals changes depending on the period of the pattern, the wavelength of the light, and the numerical aperture of the objective lens. For PC media, the reflected signal has similar polarization dependence, but this dependence is weak.