Welding in the World最新文献

The influence of external constraint time on the stress and deformation caused by laser welding of thin SUS301L stainless steel was quantitatively studied. Due to the inability to accurately control the fixture constraint time in the experiment, this paper uses a three-dimensional thermal elastoplastic finite element simulation method to study the deformation, stress, and strain changes of welded stainless steel plates under different fixture constraint times. In order to improve simulation accuracy, the relationship between mesh size and thermal input in finite element analysis is analyzed. The method of sequential coupling thermo-mechanic is proposed to analyze the transient temperature field and deformation during welding. The thermal and mechanical material properties used in the simulation follow a non-linear relationship as a function of temperature. Meanwhile, the accuracy of the simulation model was verified based on the temperature history by the K-type thermocouple and weld profile measured. The results show that the length of the clamp restraint time will indeed have a certain effect on the deformation after welding. Release of the clamp 25 s after the end of welding can effectively reduce the welding deformation from 1.3 to 1.21 mm, which is a 7% reduction.

The welding efficiency and weld formation quality of pipeline external welding are important factors that constrain the site laying speed and service performance of long-distance oil and gas pipeline. It is urgent to optimize the structure and function of pipeline welding equipment and control system, and improve the intelligent level of the external welding process. This paper focuses on improving weld bead formation quality during the pipeline all-position welding. Based on the Pieper criterion, a 5-degree of freedom (DOF) welding robot is designed. It can meet the control requirements of welding torch position and posture (WTPP) that comply with the welding process parameters at any welding position of pipeline. The kinematic model of the designed robot is established, and an analytical solution to its inverse kinematics is derived. Combined with the composite sensor based on combined laser line structured lights vision sensor and gravity sensor, the pipeline all-position intelligent welding system is integrally constructed. Based on this, the detection method of welding groove size and WTPP parameters is proposed. Through the designed program control strategy, the intelligent adjustment experiments of the WTPP were carried out during the pipeline all-position welding process. The lateral tracking deviation of welding torch was not more than 0.25 mm; the vertical tracking deviation was not more than 0.63 mm, and the posture angles feedback control deviation were not more than 0.8°. The good weld formation effect was obtained, which provides support for the improvement of the intelligent level of pipeline external welding. 

Wire arc additive manufacturing (WAAM) is an advanced and cost-effective technique for fabricating large-scale metal components; however, the process induces significant residual stress due to complex thermal cycles, leading to defects such as deformation and cracking. This study presents a generalized finite element analysis (FEA) model to investigate the temperature distribution and residual stresses evolution during the GTAW-based WAAM process. A thermo-mechanical explicit model was developed using Ansys software and validated experimentally using K-type thermocouples and X-ray diffraction (XRD) techniques. Additionally, detailed mechanical characterization, including tensile strength, impact strength, hardness, and electron backscatter diffraction (EBSD)-based microstructural analysis, was conducted. The numerical simulation demonstrated strong agreement with experimental results, with a maximum relative error of less than 8%. The findings reveal that WAAM-fabricated ER70S-6 components exhibit almost homogenous and isotropic mechanical properties throughout the build wall, indicating superior structural integrity.

This study focuses on the utilization of high-frequency mechanical impact (HFMI) treatment for rehabilitating pre-fatigued steel bridge components. It incorporates time of flight diffraction (TOFD) for precise crack depth measurement, alongside strain range drop monitoring to enhance assessment accuracy. The experimental setup involves fillet weld specimens with cope hole geometry, using S355MC steel. The HFMI treatment process employs 3-mm diameter pins to achieve an HFMI indentation depth of 0.2 mm. The study demonstrated that HFMI treatment effectively extends the fatigue life of steel bridge components, showing significant improvements for cracks up to 1.2-mm deep. TOFD measurements, validated against manual optical measurements, consistently indicated crack depths within ± 0.1-mm accuracy. This precision is critical for assessing the HFMI treatment’s effectiveness in repairing pre-fatigued structures. The strain range drop method was used as a stop criterion to evaluate crack depth in real time, effectively reducing the number of TOFD measurements required during fatigue crack growth testing. The experimental results showed that HFMI treatment could improve fatigue life, moving specimens’ performance well above the IIW recommended FAT125 curve for treated steel details. In conclusion, this investigation confirms the significant potential of HFMI treatment for extending the life of pre-fatigued steel bridge components. The combined use of TOFD and strain range drop monitoring provides a robust framework for accurately assessing and optimizing HFMI treatment.

In this research, the effects of the welding angle on the behavior of the molten pool, keyhole, and welding defects in the laser-MAG hybrid welding process of 14-mm-thick AH36 high-strength shipbuilding steel are thoroughly analyzed. High-speed photography was used to observe the behavior of the molten pool and keyhole, while synchronized oscilloscope measurements revealed a strong correlation between arc voltage fluctuations and keyhole oscillation frequencies, demonstrating the dynamic interplay between arc plasma and keyhole stability. The results reveal that the welding angle significantly affects the quality of weld formation, molten pool flow, keyhole behavior, collapse, and bottom hump, as well as spatter phenomena. When the welding angle is 82.5°, optimal weld formation quality is achieved, characterized by a stable molten pool shape and regular keyhole behavior. At a 75° welding angle, the molten pool shape and keyhole behavior exhibit significant instability, leading to poor weld formation. This results in the periodic formation of the narrowest throat on the surface of the molten pool, presenting a wide-narrow-wide serrated characteristic, which triggers surface collapse and hump defects. Furthermore, at a 97.5° welding angle, intense unstable fluctuations occur within the molten pool, causing the molten metal to overcome surface tension and bulge beyond the surface of the molten pool, forming violent fluctuations and a raised liquid column that progressively detaches from the molten pool to form spatter. The research findings indicate that an appropriate welding angle can optimize the behavior of the molten pool and reduce welding defects.

This study deals with the validation of the fatigue design values given in the IIW Recommendations for the HFMI Treatment for HFMI-treated steel joints under bending loading. In total, ten data sets involving T-joint specimens under bending loading with varying specimen geometries and base material yield strengths are investigated. The load stress ratio was R = 0.1 in all test series. The corresponding FAT-classes are defined on the basis of the IIW Recommendations for the HFMI Treatment in dependence of the structural detail and the yield strength of the base material. Furthermore, the thickness as well as certain thinness effect is covered by an IIW-recommended factor f(t) in one case leading to a design curve HFMI-IIW with f(t). In another case, a factor k_tb based on the British Standard BS 7608 is additionally considered, which combines the thickness as well as bending effect. The corresponding design curve is denoted as HFMI-IIW with k_tb. A comparison of the fatigue test data points and the related statistically evaluated S/N-curve for each data set with the two approaches reveals that the design curve HFMI-IIW with f(t) leads to a conservative assessment for all data sets involved in this study. Also, a certain thinness effects is well covered and still a proper fatigue design should be ensured. Focusing on the design curve HFMI-IIW with k_tb, which additionally covers the bending effect, a conservative assessment is observed for almost all data sets. However, it is concluded that further test data especially for reduced plate thicknesses should be assessed to provide additional comparison results and ensure a conservative applicability for HFMI-treated steel joints under bending loading in any case.

The fatigue strength of steel structures can decrease significantly when corrosion occurs. Pitting corrosion, in particular, can lead to locally high stress concentrations and may interact with existing stress concentrations from weld seams. Particularly in the case of offshore support structures, which are exposed to a corrosive environment and include several welded connections, this issue becomes relevant. Hence, in this study, butt- and fillet-welded joints of structural steel were exposed to accelerated corrosion in a salt spray chamber and then tested for fatigue strength. In order to investigate the long-term behaviour, the specimens were stored for 12 months in a salt spray chamber. Base material specimens were investigated as reference. All specimens were clean blasted and 3D scanned prior to the fatigue tests. It was shown for all specimens that the fatigue strength decreased after 12 months compared to the uncorroded reference tests. However, the fatigue reduction was different for the different geometries. The greatest reduction was observed for the base material from 282 to 122 N/mm², followed by butt-welded joints from 215 to 147 N/mm², and fillet-welded joints from 168 to 144 N/mm². As the fatigue strengths showed only minor difference after 12 months, an equalization effect can be assumed. The results show that a generalized reduction of the fatigue strength, in accordance with the guidelines, is not appropriate and therefore should be revised for a more accurate design of offshore support structures. Finally, numerical analysis based on 3D scans of the specimens was conducted and compared with the test results.

Arc-based directed energy deposition (DED-Arc) is a promising manufacturing technology on the rise in the industry. On the one hand, convincing process advantages, such as the possibility of sustainably producing complex and large-volume component geometries with comparatively high building rates, favor further industrial interest. On the other hand, there are still challenges, like the difficulty of controlling heat input and the intricate thermal history. The resulting temperature gradients and heat accumulations lead to inhomogeneous component properties and reduced process efficiency, which delays further establishment in the manufacturing industry. Therefore, implementing and developing concepts for thermal management in DED-Arc is necessary. The study examines how controlling the substrate temperature can affect the dimensional accuracy, microstructure, and hardness of DED-Arc components. Different preheating and in situ cooling strategies were developed based on numerical investigations, including a water-cooled in situ cooling unit, a cobot-guided inductor, and classical preheating approaches. The findings indicate that substrate tempering significantly impacts the penetration zone and heat-affected zone dimensions, layer widths, microstructure, and hardness profiles. A special combination of preheating and in situ cooling resulted in enhanced substrate bonding, uniform layer widths (4.0 ± 0.1) mm, and consistent hardness values (142 ± 10) HV due to a more uniform microstructure. These results indicate that integrated substrate plate tempering can significantly improve thermal process control in DED-Arc, supporting its further industrial establishment.

Low transformation temperature (LTT) welding consumables represent an innovative approach to realize compressive residual stress in the weld seam and HAZ. LTT welding consumables use the volume-expanding martensitic phase transformation near room temperature to generate compressive residual stress during cooling. This article focuses on the weld geometry and its influence on residual stress reduction using an LTT welding consumable. For this purpose, layers with an LTT welding consumable were additionally applied to the front sides of conventionally welded longitudinal stiffeners. Different weld geometries of the second weld seam could be realized by varying the welding parameters. These samples were analyzed for geometric parameters, chemical composition, and residual stress. While the chemical composition and martensite start temperature (M_S) were only slightly influenced by parameter changes, a clear influence with regard to residual stress and weld geometry was observed. Depending on the shape of the second LTT weld seam, residual stress reductions of 200 to 500 MPa were achieved using the same LTT welding consumable.

The mechanical properties of P92 (9Cr-0.5Mo-1.8W-VNb) steel weld joints, fabricated through tungsten inert gas (TIG) and activated TIG (A-TIG) welding, were compared. The non-monotonous variations in tensile and creep properties across the heterogeneous microstructural regions of both the weld joints were obtained using small specimen testing techniques. The A-TIG weld joint showed higher tensile strength than conventional TIG weld joint. The weld metal of A-TIG showed better creep resistance compared to the other zones of the A-TIG as well as all zones of the conventional TIG weld joint. The activation energies under creep for both the weld joints were found to be in the range of 385–418 kJ/mol, indicating that dislocation creep is the governing creep mechanism under investigated conditions. The low cycle fatigue behaviour of both the weld joints were evaluated under the applied strain amplitudes between ± 0.25 and ± 0.6% at room temperature and at 873 K. Both the weld joints exhibited continuous cyclic softening before a drastic reduction in the stress value due to the macrocrack propagation and eventual failure. The A-TIG weld joint showed better fatigue life than conventional TIG weld joint.