Welded Structures Research Articles

Development of in situ MMC joint using friction stir spot welding of Al6061-T6

In this study, friction stir spot welded joints of Al6061-T6 were obtained using silicon carbide particles as reinforcement. The effect of reinforced particles along with process parameters was analyzed in terms of tensile-shear strength, weld structure, and hook formation. The investigations revealed that tensile-shear strength increased by 29.78% with incorporation of silicon carbide particles in the weld region. The guiding hole diameter was found to be a significant parameter for improved weld strength. Optimal levels of tool rotation speed, pre-dwelling time, and guiding hole diameter were observed as effective process parameters for better weld quality. Weld cross sections were studied under a stereo zoom microscope and an optical microscope to observe different bonding regions. The scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) confirmed the presence of silicon carbide particles in the weld region.

Interfacial evolution of titanium/steel clad plates during pulsed tungsten inert gas welding

Joining titanium alloy with steel has important applications in the shipbuilding and aerospace industries. Successful titanium/steel joints fabricated by explosive welding have been reported recently. However, explosive welding is not ideal for welded structures with complex geometry. Here, pulsed tungsten inert gas (TIG) welding is introduced to promote the application of explosively welded transition joints. In this work, pulsed TIG of commercially pure titanium to mild steel with an explosively welded titanium/steel transition joint was carried out. The results showed that at peak current (Ip) ≤ 260 A, the TiC layer hampered the generation of FeTi and Fe2Ti. However, at Ip = 300 A, the TiC layer broke up, which resulted in the thickness of FeTi and Fe2Ti increasing sharply to 0.8 μm.

Prediction and Validation for Welding Deformation of the Upper Port Stub

The vacuum vessel (VV) as an ultrahigh vacuum pressure vessel is one of the essential components of the Chinese Fusion Engineering Test Reactor (CFETR) device. VV has strict position tolerance. The VV port stub is a typical large-scaled welded structure manufactured by electron beam welding (EBW) technique. Welding has the most significant influence on deformation. Therefore, it is essential to analyze welding deformation. A systematic welding simulation method aimed at welding deformation controlling for a large EB welded structure is proposed in this article. First, the dynamic process of EBW of 50-mm-thick ultralow carbon austenitic stainless steel was simulated based on the thermal elastoplastic theory. The weld forming mechanism of high energy density welding of the thick plate was revealed. Then the inherent strain extracted from the results of the simulation of local welding was introduced to the simulation of tailor welding of the port stub. Finally, optimal welding sequence and clamping conditions were obtained, and the reliability of the simulation was verified by the profile measurement results of the inner shell of the upper port stub.

Methods and Equipment for Experimental Evaluation of the Performance of Shell and Hull Structures

Introduction. Pressure-operated thick-walled hull structures are the most common type of high-duty welded structures. When these structures are loaded with internal pressure, a complex biaxial stress field arises in them, which is summed up with the fields of residual welding stresses. Therefore, when selecting a technology for manufacturing critical welded structures, the results obtained during conventional uniaxial tests of samples are insufficient. The variety of factors affecting the performance of structures, and the difficulties of separate assessment of their influence, caused the need to maximize the approximation of experimental conditions to the real working conditions of the structure.Materials and Methods. Testing of full-scale structures has a number of advantages, but they are extremely expensive, and, as a rule, only one, the weakest link, is identified, the bearing capacity of the other structural elements remains unclear. For testing, UDI radiometric installations designed for different sample sizes were used. The presented installations allow testing samples of various shapes, types of welded joints (butt, T-bar), changing the position of welded parts.Results. Without rejecting the results obtained during the testing of full-scale structures in the works of the Bauman Moscow State Technical University, DSTU, NRC «Kurchatov Institute» – CRISM «Prometey», and the authors proposed to conduct the basic scope of the research on individual structural elements that would reflect the characteristic features of loading, manufacturing technology, and operating conditions. The design of the «fitting-sheet» connections was applied, which made it possible to increase the indicators of the failure initiation and propagation to the level of the base metal.Discussion and Conclusions. Schemes of structures for obtaining a biaxial tension or bending field in samples were presented. Samples tested according to the proposed schemes allowed us to draw conclusions about the performance of welded joints under conditions close to the actual operation of the structures under study. The proposed test scheme is used by research laboratories in our country and around the world.

Numerical study on the strain capacity of girth-welded X80 grade pipes

Strain capacity is an important performance indicator for designing and evaluating high-grade steel pipelines. Due to the inhomogeneity of material properties in welded structures, girth welds are one of the main factors that restrict the strain capacity of pipelines. In this paper, girth-welded pipes with cracks in the inner surface of the weld have been studied, and the ductile crack initiation and propagation behavior have been simulated using the Gurson model. The corresponding nominal strain at the onset of crack initiation was defined as the characteristic value of strain capacity. The influencing factors on the strain concentration area, strain concentration factor, and strain capacity of girth-welded pipes were quantitatively analyzed. A semiempirical calculation formula for the strain capacity of typical girth-welded X80 grade pipes has been proposed as a function of the crack size, mismatch coefficient of the weld, and softening degree of the heat affected zone (HAZ). This study can facilitate the defect assessment of girth-welded pipes.

Influence of inoculants on the features of weld structure formation in low-alloyed steels (Review)

The Paton Welding Journal, 2022, №09. International Scientific-Technical and Production Journal «The Paton Welding Journal» «The Paton Welding Journal» has been published monthly since 2000 in English, ISSN 0957-798X. «The Paton Welding Journal» is a cover-to-cover English translation of the «Avtomaticheskaya Svarka» (Automatic Welding) journal. The «Avtomaticheskaya Svarka» journal has been published monthly since 1948 in Russian, ISSN 005-111X.

Research of accidents pipelines

The durability and reliability of operation of steel pipelines of water supply and sewage systems is determined in particular by the quality of their welded joints, which in turn depends both on the composition of the materials used in their manufacture and on the observance of welding technology. The composition of impurities of transported liquids, which can cause corrosive destruction of materials, also has a significant impact on the reliability of pipeline systems. These phenomena are especially important in hot water supply and industrial drainage systems, where the destructive influence of physical factors and the chemical composition of the environment can be decisive. It was found that the loss of strength of the pipeline is caused in particular by improper operation, under the conditions of which micro-flaws of welded joints of pipelines appear, which leads to their destruction. The results of examinations and experimental studies of the strength of welds of steel process pipelines are presented. An external inspection was carried out, determination of the structure and strength parameters of pipeline welds, layer-by-layer analysis of corrosion damage on their inner surface. It was found that premature destruction of welded joints of hot water supply pipelines and industrial sewage is caused by long-term operation in a stressed state. Under such circumstances, the uneven coarse-grained structure of the seam, the presence of non-metallic inclusions in the metal structure, and violations of the welding technology had a critical impact on the loss of strength. In order to increase the corrosion-mechanical resistance of welded joints of industrial pipelines, it is necessary to modify the surfacing metal of the weld to break down the structure and significantly reduce non-metallic inclusions, as well as to improve the technology of manual arc welding with coated electrodes, in particular, the root layers of welding seams.

Numerical simulation of residual stress of butt-welded joint involved in complex column-beam welded structure

The objective of this work is to clarify the effect of the structural restraint and the adjacent welded joints in column-beam welded structure on the final residual stress distribution and its evolution process of the butt-welded joint between the diaphragm and the flange through numerical simulation method. Based on ABAQUS software, a three dimensional thermal-mechanical coupled method was developed to predict the residual stress distribution for multi-pass welded joints. To improve calculation efficiency, an effective computational approach that combines a relatively coarse mesh design and an instantaneous heat source model was proposed to analyze the residual stress distribution for complex welded structures. Firstly, both a fine mesh model with moving heat source and a relatively coarse mesh model with instantaneous heat source were employed to predict the residual stress distribution in the same thick-plate butt-welded joint made of high strength low alloy steel. The computational accuracy of the proposed computational method was verified through comparing the results of the fine mesh model with moving heat source and the corresponding experimental data. Then, the residual stress distributions of the column-beam welded structure, the butt-welded joint under structural restraint condition and free state were calculated using the proposed computational approach. Results suggest that the structural restraint and the adjacent welded joints in the structure have a significant effect on the residual stress distribution.

Development of Microstructure and Mechanical Properties of TiAl6V4 Processed by Wire and Arc Additive Manufacturing

Wire and arc additive manufacturing (WAAM) has the potential to significantly reduce material waste due to the milling of components made of TiAl6V4 (Ti‐64). To keep up with the market development, this resource‐efficient technology is becoming increasingly important to achieve climate policy goals. Therefore, this study not only focuses on the influence of different process parameters, such as torch and wire feed speed, but also different gas mixtures on the microstructure and related mechanical properties, as well as on the scalability by investigating single‐ to multilayer welded structures. The wire feed speed is found to have a major influence on the geometry and mechanical properties. The use of different process gases, i.e., argon (Ar), helium (He), and a mixture of 70% He and 30% Ar neither significantly affect the microstructure nor the mechanical properties. It is also found that a solution heat treatment followed by an annealing step degrades mechanical properties, while an ordinary stress‐relief heat treatment leads to improved mechanical properties. It is shown that by adapting WAAM process and heat treatment parameters, mechanical properties of additively produced specimens can be achieved, which are fully comparable to milled components.

Fatigue performance investigation on the automotive welded structure under damped loads using the Taguchi method

AbstractIn the present paper, a three‐dimensional numerical model has been built using ANSYS code to analyze the static and fatigue behavior of a welded design based on four rectangular profiles under damped loads for automotive application. The fatigue of the proposed design is generally influenced by a number of factors. The aim of this study is to investigate the effect of the load level, the stress ratio, the mean stress theory, the geometry size, the weld bead height, the temperature of the weld bead on the durability (P1), and the maximum of von Mises stress (P2) at the critical areas in the welded structure. As well as the length and the stiffness of the spring have been furtherly investigated. For this purpose, the application of the Taguchi method with computational simulation was performed for the target to determine the optimum operating parameters conditions. The results indicated that the optimum levels yielding a higher performance for P1 and P2 were (L1, L2, L2, L3, L1, L1, L3, and L3) and (L2, L3, L3, L3, L3, L3, L3, and L2), respectively. Thus, it revealed that the weld temperature was the predominant parameter influencing P1 and the mean stress theory factor was the most significant parameter influencing P2. This study led to defining a regression equation relating the output parameters with the selected factors. Consequently, the percentage error between regression equation calculations and computational outputs of fatigue life and maximum von Mises stress corresponding to the most optimal combinations obtained from Taguchi calculations was 0.92% and 0.63%, respectively. In fact, several parameters have been employed in this durability assessment to characterize the behavior of welded rectangular profiles prototype to predict the overall behavior of the suspension system of the automotive.

A novel generalization ability-enhanced approach for corrosion fatigue life prediction of marine welded structures

A generalization ability-enhanced approach for corrosion fatigue life prediction was proposed. The data augmentation and analysis of influence factors were conducted via Borderline-SMOTE and XGBoost algorithms to improve the prediction accuracy. The results of weight analysis were integrated into DCNN model via Attention mechanism. The average error and error standard deviation of the proposed model were more than 89.8% and 87% smaller than that of exiting models, respectively. The average gradient-signal-to-noise-ratio was introduced to evaluate the generalization ability of the proposed model, which was significantly higher than that of the linear regression. The predicted results under different stress ratios, frequencies and environmental conditions emphasized the good prediction accuracy and generalization ability of the proposed model. Consequently, the proposed method could reduce the consumption of fatigue test and evaluate the reliability of engineering components, which could provide a technique support for the intellectualization and digitization of fatigue behavior of offshore platforms welded joints.

MIG WELDING OF AUSTENITIC 316L STEEL USED IN MEANS OF TRANSPORT

The austenitic 316L steel (1.4401) is an important stainless material used to build various means of transport. Austenitic steel has high resistance to atmospheric corrosion. The austenitic steel is treated as a good weldable material, although cracks are possible. This paper analyses the influence of various MIG welding parameters on the creation of correct joints used in the stainless steel structures of mobile platforms elements, as an example of welding structures, in various means of transport. Various tests verifying the mechanical properties of MIG welds, including non-destructive tests, tensile strength and hardness tests, were carried out. This article aims to show how important and complex the task is to select the correct welding parameters for elements of means of transport made of austenitic steel on the example of elements of mobile platforms.

Reduction Characteristics of Welding Deformation According to Cooling Distance in Heat Sink Welding

When assembling a welding structure, welding deformation occurs inevitably due to the locally applied heat source. This not only decreases the strength of the structure but also decreases productivity efficiency. In recent years, in-process control welding by an additional cooling source has been applied for thin-plate structures. In the present study, a numerical analysis of Heat Sink Welding (HSW) was performed to examine the effect of the heat sink source on the degree of welding deformation. Then the numerical result was compared with that of conventional welding. Moreover, the result predicted from the numerical analysis was compared with the experimental result on displacement to be validated. As a result, a cooling zone appeared on the welding metal surface. In the case of the heat-affected zone (HAZ), it was confirmed that the maximum temperature decreased from 596 to 545 K compared to the conventional welding method. In addition, the displacement in the thickness direction decreased by about 5%, from 0.83 to 0.79 mm. The overall results obtained in numerical analysis indicated that the cooling efficiency significantly increases as the cooling distance is shorter.

Investigating influence of external restraint on welding distortion in LAHS steel thin-plate structures by means of integrated computational approach

In order to ensure the dimensional accuracy during welding assembly, external restraints are often used to control welding-induced distortion. The objective of this study is to investigate the effectiveness of external restraints on the reduction of welding distortion in low alloy high strength (LAHS) steel thin-plate panel structures with different plate thickness by means of an integrated computational approach. In the current study, the total deformation of LAHS steel thin-plate welded structure was computed by a two-step integrated computational approach which combines the thermal elastic plastic finite element method (FEM) with the elastic FEM based on inherent strain theory. In the integrated computational approach, the thermal elastic plastic FEM was employed to obtain the inherent deformations of each typical joint involved in the thin-plate welded structure at the first step, and then the elastic FEM based on the inherent strain theory was used to estimate the total deformation of the whole thin-plate welded structure. Firstly, the integrated computational approach was used to simulate the buckling distortion in a thin-plate panel structure, and the corresponding experiment was carried out to verify its computational accuracy. Then, two finite element models with plate thickness of 5 and 12 mm were established to clarify the effectiveness of external restraint on the reduction of welding distortion of the thin-plate welded structures. The simulated results suggest that external restraint could not effectively prevent the occurrence of buckling distortion for the thin-plate structure with 5 mm thickness, while it can reduce the out-of-plane deformation to a large extent for the thin-plate welded structure with 12 mm thickness.

Effects of Ti, B and O on Weld Structure and Impact Toughness of High Heat Input Flux Cored Wire

Effects of Ti, B and O on Weld Structure and Impact Toughness of High Heat Input Flux Cored Wire

Combined experimental/theoretical approach to residual stresses within multiplicative elasto-plasticity

The study is devoted to geometrically non-linear modelling of viscoplastic structures with residual stresses. We advocate and develop a special approach to residual stresses based on the transition between reference configurations. The finite strain kinematics of the viscoplastic material is modelled by the multiplicative decomposition of the deformation gradient tensor. Numerical algorithms originally developed for unstressed materials are extended to materials with pre-stresses. Owing to the weak invariance of constitutive equations, the incorporation of pre-stresses happens without additional costs. Thus, the advocated approach is especially efficient. A novel experimental/theoretical method for assessment of residual stresses in welded structures is presented; the method combines advantages of purely experimental and theoretical approaches. To demonstrate the applicability of the proposed procedure, we simulate plate welding. As an example we show that the procedure allows extrapolation of the field of residual stresses away from the measurement points. As another example, we address the reduction of weldment-related residual stresses by mechanical treatment.

Hybrid resistance-laser spot welding of aluminum to steel dissimilar materials: Microstructure and mechanical properties

In this work, an innovative hybrid resistance spot-laser welding process, which first conducts resistance spot welding of aluminum and steel dissimilar materials, followed by laser spot welding, is proposed to join aluminum to steel. Through innovative designing of the electrode structure, the welding current distribution and the weld structure were optimized to produce a thin and uniform intermetallic layer with its thickness below 1.2 μm. Furthermore, the faying interface morphology of aluminum and steel dissimilar materials was changed from a traditional flat surface to an interface with a deep bulge into the aluminum weld. It was found that resistance spot weld had a considerable tensile-shear load but poor ductility and energy absorption due to the presence of a weak bonding area around the periphery of the joint, where facilitated the crack initiation and rapid propagation. The following laser spot welding process was conducted in the weak bonding area of the resistance spot welding joint, which inhibited rapid propagation of the cracks along the faying interface avoiding the interface fracture. Compared with resistance spot welding joints, the tensile-shear peak load and energy absorption were increased by 18.2 % and 424.8 % for hybrid welding joints, respectively.

Analysis of the Relaxation Process of Welding Residual Stresses Using a Combined and Nonlinear Hardening Model

This article applies a combination of hardening models to analyze the relaxation process of residual stresses. The obtained results can be used to estimate the final stress state in welded structures after the load application. This work begins by modeling the evolution of residual stresses produced by the thermal cycle during welding process. Subsequently, this stresses obtained by finite element calculations will be subjected to a mechanical relaxation process. In order to ensure the accuracy of the relaxation model, the plastic behavior of the material has been integrated by modeling two non-linear hardening models, which are combined and applied in the same relaxation process. The results have made it possible to visualize the final state of the residual stress field after relaxations. Then these results are analyzed in order to assess the impact of plasticity on the relaxation process.

Modelling on CVN Toughness of Weld Deposits

The Charpy V Notch toughness (CVN) of steel is an important property while considering structural and heavy loading conditions. In welded structures, CVN is attributed to many variables like composition of steel, heat input of welding, pre- and post-heat treatments of the weldment, type of welding process etc. The regression analysis works accurately for three to four variables. The property of weldment is associated to more than three-four variables. So this conventional regression analysis couldn’t capture associated trends among the variables due to their non-linearity. This complexity is countered well by artificial neural network (ANN) modelling. In the present work, artificial neural network approach is utilized for the prediction of CVN of ferritic steel welds, which is multi-phase complex engineering material. The multilayer perceptron (MLP) method is used for formulating the neural network models. Numerous models were made by adjusting the hyperparameters and a best model was selected having least training error. The crucial results obtained from this model where analysed from response graphs and contour plot. This (MLP) approach for formulating neural network model was proved to be efficient after validation procedure and the same model could be exploited well for predicting accurate value of CVN in a very time and cost-effective manner.

Influence of cooling conditions on the microstructure and impact strength of welded joints made by automatic submerged multi-arc welding

The aim of the work was to study the effect of cooling rate on the formation of the structure and impact strength of a welded joint of 0,07C-1,6Mn-0,2Cr-Nb pipe steel. The cooling rate w8/5 was varied from 0.9 to 12.4 °/s in the temperature range of 800–500 °/s by changing the heat input of welding, the groove width, and the temperature of 22 mm thick plates welded on a laboratory welding stand. The conducted studies confirm the previously obtained results on the weldability of pipe steels, that a decrease in the heat input of welding and, as a result, an increase in the cooling rate of the w8/5 welded joint is accompanied by an increase in impact toughness. For the studied steel, a significant increase in the impact toughness of KCV-40 (more than 2.5 times) occurs in the range of cooling rates w8/5 from 0.9 to 7.3 °/s and is typical not only for tests along the fusion line, but also in the center of the seam weld. It is shown that with an increase in the cooling rate of the welded joint in the structure of the weld metal, the maximum length and width decrease, and, at the same time, the proportion of grain boundary ferrite crystallites. At high cooling rates, the matrix of the weld structure consists entirely of acicular ferrite, which is favorable in terms of increasing the density of high-angle grain boundaries, toughness, and cold resistance. In the heat-affected zone, with an increase in the cooling rate, the maximum and average grain sizes decrease; grain-boundary and Widmanstatt ferrite is eliminated; a completely bainite structure is formed and the proportion of lath bainite increases, which also leads to an increase in the density of high-angle boundaries and contributes to an increase in impact strength. With an increase in the cooling rate, the proportion of the MA-constituents in the structure of the seam and the HAZ are increases. It is assumed that an increase in the cooling rate, simultaneously with a favorable effect on the structure of the weld and the weld pool, reduces the time for the processes occurring in the weld pool, which can be an unfavorable factor in terms of the toughness of the weld.