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During the welding process, local heat input induces residual stress in the joint area, which significantly influences the service performance of the structure. Welding parameters, particularly the groove angle and welding speed, are critical determinants of the distribution of residual stress. In this study, a combination of finite element simulation and drilling method testing was employed to design 30 working conditions in order to analyze the coupled effect of these two factors. The results indicate that as the groove angle and welding speed increase, the longitudinal residual stress decreases markedly, thereby providing valuable guidance for process optimization.

High-pressure steam pipes inevitably suffered from the reciprocal interaction of high pressure and temperature during a long-period service, causing deformation and cracking. However, only limited studies about abnormal bulging caused by condensed water have been carried out. To study the relationship between bulging and condensed water, bulging tee joints belonging to high-pressure steam pipes were investigated with a macro visual inspection, chemical composition analysis, and metallographic microscopy. According to the analysis of the bulging samples, pearlite spheroidization was found in the abnormal bulging tee joint. The ANSYS FLUENT modeling indicated that the tube wall of bulging tees was continuously subjected to alternating stress, causing the cyclic transformation of the liquid–gas phase inside the tee joint. The results indicate that the stress produced by a condensed water droplet ranges from 532.8 MPa to 59 MPa, continuously exerting pressure on the tube wall of the tee joint. When combined with the variation in the temperature field, the temperature of the severe bulging tee joint and slight bulging tee joint alternates. Further modeling illustrates that the stress generated by the impact of condensed water droplets on the high-temperature tee joints causes a ratcheting effect, which is identified as the main factor contributing to the bulging of the tee joint. Deterioration of the microstructure is considered a secondary mechanism.

Modern structural engineering is impossible without the use of materials and structures with high strength and low specific weight. This work carries out a quantitative and qualitative analysis of articles for 2016–2021 on the topic of welding of dissimilar alloys. It is found that laser welding is most widely used for such metal pairs as Al/Fe, Al/Ti, and Al/Cu. The paper analyzes the influence of the basic techniques, methods, and means of laser welding of Al/Fe, Al/Ti, and Al/Cu on the mechanical properties and thickness of the intermetallic compound (IMC). When welding the lap joint or spike T-joint configuration of Al/Fe, it is preferable to melt the steel, which will be heated or melted, by the laser beam, and through thermal conduction, it will heat the aluminum. When welding the butt-welded joint of Al/Fe, the most preferable is to melt the aluminum by the laser beam (150–160 MPa). When welding the butt-welded joint of Al/Ti, it is possible to obtain the minimum IMC and maximum mechanical properties by offsetting the laser beam to aluminum. Whereas when the laser beam is offset to a titanium alloy, the mechanical properties are 40–50% lower than when the laser beam is offset to an aluminum alloy. When lap welding the Al/Cu joint, under the impact of the laser beam on the aluminum, using defocusing or wobbling (oscillation) of a laser beam, it is possible to increase the contact area of electrical conductivity with the tensile shear strength of 95–128 MPa.

Pumped storage power plants (PPSPs) have attracted significant attention for their contribution to grid stability. An increasing number of power plants choose to be buried deep underground and designed with long penstocks. However, in high-head power plants, water hammer waves are prone to accumulation and diffusion, triggering vibrations in the pipeline and mountain. Therefore, the aim of the present study is to clarify the fluctuation characteristics in the fluid and further investigate the dynamic response of the penstock-mountain system under oscillation. This study adopts a 3D Fluid-Solid Coupled method to calculate and analyze the fluctuations and stresses across the studied area under the condition of load rejection without closing the spherical valve of the units. The results show that during the load rejection process, there is a violent fluctuation period, with the maximum peak-to-peak amplitude reaching 0.937 MPa. Based on this period, further analysis reveals that there are stress-concentrated areas near the T-joint. The maximum principal stress (MPS) at T-joint can reach more than 4.55 MPa, with a large oscillation intensity. In violent period, as depth increases, the contribution of Norm Z stress in mountainous areas grows, accompanied by changes in frequency characteristics and amplitude. The simulation method proposed in this paper can be extended to other penstock-mountain systems, providing references for the safe operation of PPSPs.

The non-destructive full-field non-contact thermographic technique is applied for non-destructive flaw detection of the welded joints, in real-time and offline configuration. In this paper, a thermographic procedure for real-time flaw detection in manual arc welding process is presented. Surface temperature acquisitions by means of an IR camera were performed during arc welding process of 8 specimen both for calibration and validation of the numerical model. The investigated variables are the technique (manual stick arc (SMAW) and gas arc (GMAW) welding) and the joint shape (butt and T joint) for steel joints, in sound conditions and with artificial flaws. Numerical simulation of welding thermal transients was run to obtain the expected surface temperature fields and thermal behavior for different welding parameter configurations. Hardness measurement and micro-graphic analysis were performed to validate numerical simulation results. The real-time thermographic study of the weld pool gives direct indications of anomalies; local studies of the thermal transient and thermal profiles can detect some kind of flaws; microstructural analysis of Heat-Affected Zone (HAZ) and surrounding areas higlights the presence of austenite and martensite distribution which justifies the thermal transients and thermal profiles for different welding configurations. Comparing real-time IR acquisition of the welding process with simulated thermal contours of sound processes provides information of presence of some kind of flaws. Since most of the flaws are generated in the weld pool, it is possible to recognize anomalies directly from the thermal acquisitions or with post-processing the acquired data.

In this paper, an experimental study of pull-off load-bearing capacity and damage mode was conducted for tenon-and-mortise glued T-joints of composite honeycomb sandwich structures. Five test pieces of T-joints with different tenon widths and different numbers of tenons with the same total tenon width were investigated. The results of the pull-off tests showed that the tensile failure of the gluing surface occurs first in the tenon shoulder region during loading of the T-joint, after which the tenon region takes most of the load until the shear failure of the gluing surface of the bottom plate and the web in the tenon region or the panel pulls off. For the composite honeycomb sandwich structure tenon-and-mortise glued T-joints, increasing the width of the tenon makes an important contribution to improving the pull-off load capacity of the T-joints; when the total width of the tenon is the same, the pull-off load capacity of the T-joints decreases when the number of tenons increases.

This paper focuses on the T-joints of 3mm thick 5083 aluminium alloy, and the study was conducted by the self-designed welding tool. The results indicated that the trials achieved well-formed, defect-free welds with fillet transitions, and the weld areas experienced varying degrees of thinning. Microstructural analysis indicates that the grains are in equiaxed crystalline state around the nugget zone (NZ), while grown larger within the heat-affected zone (HAZ). The minimum tensile strength have reaches 306 MPa, exceeding 95% of the base material (BM), with fractures occurring in the base material area. The hardness distribution in descending order is NZ, BM and HAZ. Theoretical foundation and technical support are provided for the high-quality welding of thin aluminium alloy plates and has guiding significance for welding applications in production processes.

The high-strength low-alloy S460ML and S460N steels were chosen for underwater wet welding of dissimilar T-joints using covered electrodes. For improving the quality of joints, the temper bead welding (TBW) method was used. The application of TBW in pad welding conditions has been investigated earlier but the possibility of usage of this technique in welded joints was not analyzed. The main aim of the study was to check the influence of TBW on the hardness and structures of the heat-affected zone (HAZ) of dissimilar T-joints made in the underwater conditions. The experiments conducted showed that the technique used can reduce the susceptibility to cold cracking by decreasing the hardness in HAZ, which is a result of changes in its structure. The TBW technique reduced the hardness in the HAZ of the S460N steel by 40–50 HV10 and in S460ML by 80–100 HV10. It was also found that the changes in S460ML and S460N were much different, and therefore, the investigated technique can provide better results in the steel characterized by lower carbon equivalent Ce IIW .

One of the main challenging issues in friction stir welding (FSW) of stiffened structures is maximizing skin and flange mixing. Among the various parameters in FSW that can affect the quality of mixing between skin and flange is tool plunge depth (TPD). In this research, the effects of TPD during FSW of an Al-Mg-Si alloy T-joint are investigated. The computational fluid dynamics (CFD) method can help understand TPD effects on FSW of the T-joint structure. For this reason, the CFD method is employed in the simulation of heat generation, heat distribution, material flow, and defect formation during welding processes at various TPD. CFD is a powerful method that can simulate phenomena during the mixing of flange and skin that are hard to assess experimentally. For the evaluation of FSW joints, macrostructure visualization is carried out. Simulation results showed that at higher TPD, more frictional heat is generated and causes the formation of a bigger stir zone. The temperature distribution is antisymmetric to the welding line, and the concentration of heat on the advancing side (AS) is more than the retreating side (RS). Simulation results from viscosity changes and material velocity study on the stir zone indicated that the possibility of the formation of a tunnel defect on the skin–flange interface at the RS is very high. Material flow and defect formation are very sensitive to TPD. Low TPD creates internal defects with incomplete mixing of skin and flange, and high TPD forms surface flash. Higher TPD increases frictional heat and axial force that diminish the mixing of skin and flange in this joint. The optimum TPD was selected due to the best materials flow and final mechanical properties of joints.

Oil and gas pipeline construction has been experienced for more than 200 years. With the development of the world economy, the demand for oil and natural gas is increasing. X80 steel is a kind of high-strength pipeline steel widely used in pipeline engineering at present. Pipeline steel is developed by adding a small amount of alloying elements and improving the rolling process under the low C-Mn-Si system. In this paper, the X80 steel T-joint is taken as the research object, the finite element simulation is used to analyze the fracture of the T-joint, and the change law of the fracture parameters of the crack tip under different stress states is studied. The research shows that the welding crack at the fusion line (FL) is the most dangerous, which can provide a certain reference for pipeline engineering.