ABSTRACT Reliability, safety, and the lifetime of wind energy systems are mainly driven by the quality of each single component. Especially, large structures made of cast material or welded structures, such as the nacelle, the machine carrier, or the tower, are subjected to cyclic loading. In these cases, various factors determine the fatigue strength and thus the reliability. For castings, local material defects and the local microstructure are the relevant properties; for welded joints, the weld geometry and weld imperfections. While new and practical methods to assess the influence of defects resp. imperfections on fatigue strength are needed, wind energy components can profit from new cast materials and welding procedures with improved properties to enable a lightweight and more reliable component design. The paper discusses reliability aspects and the lifetime assessment of cast and welded wind energy components based on production quality and connected size effects. Therefore, new methods based on the quality assurance process are presented coupling digital nondestructive test results with local fatigue strength of cast and welded components. Moreover, newer achievements in improved materials and production quality and their benefit for lifetime and lightweight are discussed based on modern cast iron materials like high‐silicon nodular cast iron.

Effects of activating fluxes on geometry, microstructure, and hardness of duplex stainless-steel welds produced by GMAW with 316 L base metal

Abstract In this study, dissimilar butt welding of 0.8 mm thick DP600 and 1 mm thick DP1180 advanced high-strength steels was performed using fiber laser beam welding with beam oscillation. The effects of oscillation type (linear and circular), oscillation amplitude (0.5, 1, 1.5 mm), and welding speed (50–80 mm s −1 ) on weld bead geometry, microhardness, and tensile load were investigated. A total of 12 experimental sets were conducted by keeping the laser power and frequency constant at 1.2 kW and 100 Hz, respectively. Metallographic evaluations, Vickers microhardness tests, and tensile tests were carried out in accordance with standard procedures. The results revealed that welding speed had a significant influence on weld penetration and width, with optimal parameters determined as 60 mm s −1 speed and 1 mm amplitude in both oscillation types. Circular oscillation generally led to higher microhardness values, whereas linear oscillation produced wider weld seams. While amplitude increase decreased penetration depth, it improved weld width. The tensile load of all joints was largely influenced by the DP600 base metal, where fractures were consistently observed. However, the joint at 1.5 mm amplitude in circular mode fractured in the weld zone, indicating insufficient penetration. The findings suggest that proper selection of oscillation parameters can enhance weld quality and mechanical performance when joining dissimilar high-strength steels for lightweight automotive applications.

Inconel 625 is widely employed in high-temperature and corrosive environments, where the integrity of welded joints critically influences component performance. This study systematically investigates how laser beam welding (LBW) heat input governs cooling behaviour, microstructure evolution, elemental segregation, and the mechanical performance of Inconel 625 weld joints aiming to become sustainable joints. A single-spot monochromatic non-contact type infrared pyrometer is used to monitor the thermal cycles of the molten weld pool and the cooling rate and melt pool lifetime were determined based on the thermal cycle data. The impact of cooling rate and melt pool lifetime on weld geometry, microstructure, micro-segregation, and mechanical properties were thoroughly investigated. The findings revealed that the fibre laser welding produced sound, defect-free joints across all experimental heat-input conditions and the weld quality was fairly dictated by cooling rate during solidification. Reducing heat input (by using faster laser scan speeds) increased the cooling rate (1.45 × 103 to 3.65 × 103 °C/s), resulting in a shortened melt-pool lifetime and altered weld bead geometry from hourglass to truncated-cone profiles. Eventually, the fusion-zone microstructure transitioned from coarse cellular/columnar dendrites at high heat inputs to refined dendrites at low heat inputs. The EDS analysis revealed pronounced Nb and Mo segregation in slowly cooled welds and Laves phase formation due to insufficient time for solute redistribution and γ-Ni matrixes were consistent noted with XRD-observed peaks. The presence of the brittle Laves phase adversely affects the microhardness and tensile strength of the weld joints. Mechanical testing confirmed that decreasing heat input (in faster laser scan speeds) enhanced micro-hardness and tensile strength due to grain refinement and solute entrapment in the γ matrix. The highest joint strength (989.3 ± 10.4 MPa) and elongation (40.3 ± 1.8%) approached those of the work material, and these findings establish processing parameter–structure–property relationships for the LBW of Inconel 625. The co-relation in the present manuscript can be used in the future for process monitoring and for controlling the mechanical properties of laser welding and may provide a practical guidance for optimizing weld quality in advanced industrial applications.

Laser welding is one of the most promising methods of joining metals, combining high precision, minimal thermal deformation, and the possibility of process automatization. Due to the high energy density of the laser beam, the technology provides deep penetration with a narrow heat-affected zone, making it effective for welding corrosion-resistant austenitic steels, in particular AISI 304. At the same time, the peculiarities of thermal processes in laser welding, such as intense heating and rapid cooling of the metal, significantly affect the formation of the structure and properties of the welded joint, so the choice of optimal modes is crucial for preventing defects and ensuring high quality of the welded joint. The paper presents the results of an experimental and statistical study of the laser welding process of 1.5 mm thick AISI 304 steel using response surface methodology (RSM). The aim of the study was to determine the patterns of influence of the main parameters of laser welding on the formation of the geometry of the welded joint. Based on a factorial experiment, regression models were developed to describe the change in the area and width of the weld depending on changes in process parameters. Analysis of the results has shown that the main factors determining the geometry of the joint are the power of the laser radiation and the welding speed. Increasing the laser power contributes to an increase in the weld area, while increasing the speed reduces it. At high values of laser radiation power, the process becomes more stable, and the weld geometry becomes less sensitive to parameter changes. Laser beam defocusing has a negligible effect, only slightly increasing the width of the weld. The most pronounced interaction was found to be between power and speed, which tends to determine the maximum values of the weld area. The developed regression equations with a deviation of less than 10% confirmed the adequacy of the model and the effectiveness of using RSM to predict the geometry of the welded joint. The optimal welding modes identified in the study ensure the formation of high-quality, defect-free joints that defect-free joints and correspond to quality level “B” according to EN ISO 13919-1:2019. Keywords: laser welding, thin-walled products, welding process optimization, response surface methodology, stainless steels, AISI 304.

Abstract Surface imperfections may have a strong influence on weld quality and the fatigue life of welded joints. The relation of surface imperfections and fatigue life is given in some cases in weld quality standards like ISO 5817:2023 (Annex B). Currently, surface imperfections are determined according to ISO 17636:2017 by visual testing (VT). The aim of this study is to investigate the application of weld quality assessment by digital visual testing (D-VT) and the relation between weld quality (assessed by D-VT) and fatigue strength for the surface imperfection type “incorrect weld toe” according to ISO 5817:2023 (Annex B). Based on D-VT by 3D-scans, intermittent fillet weld specimens were classified into different quality levels according to ISO 5817 (B, C, D, and < D). Transverse stiffeners were manufactured with different weld geometries. Additionally, some welded specimens contain short surface imperfections (start-stop position), manufactured by interruption of the welding process (intermittent welds). Experimental fatigue test results revealed no significant differences in fatigue life between specimens with and without start-stop positions that are attributed to different quality levels. Although radii of less than 1 mm were observed in all specimens, a fatigue class of at least FAT71 or in most cases FAT80 was determined—contrary to ISO 5817:2023 Annex B, which suggests FAT63 in such cases. The specimens of quality level D are at least related to FAT71. Furthermore, the results reveal that short surface imperfections of the type “incorrect weld toe” that cover less than 10% of the weld length have no significant effect on the fatigue life of welds in the investigated case.

Welding is one of the most common machining methods in the industrial field, and weld grinding is a key task in the industrial manufacturing process. Although several weld-image datasets exist, most provide only coarse annotations and have limited scale and diversity. To address this gap, we constructed INWELD, a comprehensive multi-category weld dataset captured under real-world production conditions, providing both single-label and multi-label annotations. The dataset covers various types of welds and is evenly divided according to production needs. The proposed multi-category annotation method can predict the weld geometry and welding method without additional calculation and is applied to object detection and instance segmentation tasks. To evaluate the applicability of this dataset, we utilized the mainstream algorithms CenterNet and YOLOv7 for object detection, as well as Mask R-CNN, Deep Snake, and YOLACT for instance segmentation. The experimental results show that in single-category annotation, the AP50 of CenterNet and YOLOv7 is close to 90%, and the AP50 of Mask R-CNN and Deep Snake is greater than 80%. In multi-category annotation, the AP50 of CenterNet and YOLOv7 is greater than 80%, and the AP50 of Deep Snake and YOLACT is nearly 70%. The INWELD dataset constructed in this paper fills the gap in industrial weld surface images, lays the theoretical foundation for the intelligent research of welds, and provides data support and research direction for the development of automatic grinding and polishing of welds.

A probabilistic framework is developed to quantify the Degree of Bending (DoB) behavior in fiber-reinforced polymer (FRP)–strengthened tubular X-joints subjected to axial and in-plane bending loads. Despite extensive research on FRP retrofitting, the probabilistic modeling of DoB behavior in strengthened joints—across different joint types, composite systems, and loading conditions—has not been addressed. The proposed framework, therefore, represents the first systematic attempt to statistically characterize DoB in FRP-retrofitted tubular joints. The proposed model considers multiple FRP types (SFRP, GFRP, AFRP, and CFRP) and is validated against seventeen existed experimental and analytical benchmarks to ensure predictive reliability. A total of 296 finite element simulations were performed on 148 unique joint configurations, incorporating detailed weld geometry and explicit contact interactions between the FRP layers and the steel substrate. Simulation outputs were compiled into a statistical database, to which 25 candidate probability distributions were fitted. Goodness-of-fit was evaluated using Chi-squared, Anderson–Darling, and Kolmogorov–Smirnov tests. Among the tested models, the three-parameter Fatigue Life distribution demonstrated the best agreement with the simulated DoB data under both axial and bending loads. In contrast to deterministic approaches that usually give conservative results because of fixed input assumptions, the proposed probabilistic model reflects the actual variability in joint behavior. This makes it possible to carry out more realistic reliability assessments and to adjust safety factors in design practice. In engineering applications, the proposed identified distributions can be used in reliability analyses of jacket-type offshore platforms, where tubular connections are often the most vulnerable parts, helping engineers move toward performance-based design and a clearer understanding of failure probability.

The present study focuses on the finite element method simulation as well as an experimental approach to understand the effect of heat input on the weld joints. Welding process was simulated using ANSYS software to precisely predict the range of heat energy required for autogenous welding of 3 mm thick AISI 304 stainless steel plate. A three dimensional model was created and welding simulation was performed using transient thermal analysis facility available in the toolbox of ANSYS workbench. The weld geometry profile obtained from the simulations, at different heat flux input conditions were investigated, considering the temperature distribution contours. Optical microscopy was used to characterize the weld geometry profile of the weld joints obtained from the physically conducted experiments. Comparison of the weld geometry profile results obtained from both methods showed an excellent agreement with each other. Furthermore, the influence of the heat input on the mechanical properties of joints were also investigated. The tensile test results showed that the ultimate tensile strength and tensile strain of the weld joint increases as the heat input increases. The micro hardness of the weld joint obtained with 918 J/mm heat input has highest average hardness, followed by 816 J/mm and 714 J/mm heat input.

Abstract The relationship between local weld geometry and fatigue life has been extensively studied over the past decades, driven by the need to enhance structural integrity and optimize costs throughout a structure’s service life. While numerous studies have explored the influence of weld geometry on fatigue strength, the comparative effect of different welding methods under comparable weld geometry quality remains largely unexplored. Furthermore, the influence of local geometric variations for each welding method has not been systematically evaluated. This study explores a large dataset of laser-scanned butt welds, analyzing key geometric parameters. The dataset is categorized by welding method (laser-hybrid welding, submerged arc welding, and flux core arc welding), and statistical distributions are examined to assess variations in weld geometry and compliance with ISO 5817 quality groups. The characteristic fatigue life for each quality group is estimated. The correlation between geometric factor and fatigue life is evaluated through the residual analysis of stress-life curve linear fitting. According to the findings, different geometry features dominate depending on the welding method. The fracture location is strongly influenced by angular misalignment, while fatigue strength is better explained by quantile-based analysis of local geometry. These results provide a basis for future predictive modeling and quality assessment in welded structures.

Abstract Laser -hybrid welded butt joints are increasingly used in structural applications due to their high productivity. However, the complex interaction between the laser beam and arc process often leads to weld imperfections. These weld imperfections can significantly influence the development of stress concentrations on the weld surface, which can affect the mechanical properties and fatigue performance of the joints. Therefore, accurately identifying and assessing these imperfections is crucial for ensuring weld quality and structural safety. In this study, a method is proposed to assess the weld quality and numerically determine stress concentrations in laser-hybrid welded butt joints with severe imperfections using 3D scans. For this purpose, a total of 76 specimens were scanned using a high-resolution 3D laser scanner to capture the weld geometry. The scan results were then used to assess the weld quality according to the ISO 12932 standard and to generate numerical models by using the reverse engineering method for 3D finite element (FE) analysis. Additionally, fatigue tests were performed to observe the failure location for each specimen and compare it with the predicted failure location from the FE analysis. While the FE predictions could effectively highlight the critical high-stress regions, they did not consistently match the actual crack initiation sites due to the complexity and variability of weld imperfections. However, considering the micro-support effect through the theory of critical distances improved the accuracy of failure location and fatigue life predictions by accounting for the influence of local stress gradients.

ABSTRACT The objective of study is to analyze the impact of welding parameters and weld geometries on the mechanical and metallurgical properties of TIG-welded SS304 stainless steel. It is crucial because of its high strength-to-weight ratio and remarkable corrosion resistance characteristics, which are vital for many applications. The TIG-weld experiments are performed by varying wide range welding parameters i.e. current, groove angles, and root gaps. The Taguchi L8 orthogonal array was utilized to conduct experiments, by varying welding current (80–140A), groove angle (15° & 30°), and root gap at different levels, with the use of ER308L filler material. Weld microstructure, micro/macro hardness, and tensile strength of the heat-affected zone were reported. The statistical tools regression model, S/N ratio and ANOVA were used for optimization of parameters. Results revealed that increasing welding current improved tensile strength with max value of 843 MPa due to the formation of coarser austenite and dispersion of δ-ferrite and chromium carbides. However, increasing groove angle and root gap decreased tensile strength. Additionally, higher welding current and groove angles led to increased micro-hardness, while increasing root gap decreased it. The regression model contributed 88.70%, 95.94% and 91.68% of the total variability for UTS, micro and macro hardness respectively.

Artificial intelligence-assisted laser ultrasound method for the estimation of porosity in hairpin weld seams☆

ABSTRACT The effective notch stress (ENS) approach is increasingly adopted in fatigue assessments of ship structures. The ENS approach can be simplified by the ENS concentration factor (ENSCF). In this study, six typical details of longitudinal end connections corresponding to the fatigue-prone regions of double-bottom structures were designed, and then the ENS at the weld toes of the details was analyzed using the submodeling technique. The influencing factors (load and boundary condition) of the ENSCF were investigated and the statistical characteristics of the ENSCF caused by weld-shapes variations were elucidated. It was found that the ENSCF of the detailed longitudinal end connections could be appropriately calculated under the independent boundary condition. The ENSCF was consistently higher under local water pressure loading than under global hull girder bending for each structural detail. Moreover, the weld geometry significantly influenced the ENSCF of the six typical details.

Phased array ultrasonic testing (PAUT) instruments often incorporate optional weld overlays that superimpose an assumed joint geometry on the sectorial scan (S‑scan). These overlays aid interpretation and scan planning by positioning signals relative to the weld profile based on index position. Their usefulness, however, depends on user defined weld geometry and stable index position. In practice, welds frequently deviate from the assumed geometry (e.g., land height, land offset, bevel angle), which can lead to significant interpretation errors. Incorrect overlays lead to placement and characterization errors and may reinforce confirmation bias when the S-Scan image is trusted over the A-Scan signal dynamics. This paper outlines common failure modes—misplacement, false negatives, and false positives—and offers mitigation: verification of weld preparation, emphasis on echo dynamics, and training that treats overlays as aids rather than authorities. The objective is balanced use: overlays remain valuable when accurate but are never a substitute for critical evaluation of ultrasonic data.

Introduction. Increasing the productivity of single-wire surfacing through raising the wire feed rate causes defects — undercuts and poor fusion between layers, which reduces the quality of the deposited coating and increases the reject rate. To solve this problem, multiwire surfacing techniques are being developed in a shielded gas environment which increase productivity without compromising quality. The literature shows that the relative position of electrodes in multiwire systems affects significantly the thermal and electrophysical characteristics of the arc, and therefore, the geometry of the reinforcement and the shape of the fusion penetration. However, the available studies are fragmentary: there is insufficient data on the morphology of the fusion zone, and the relationship of its parameters and specific electrode arrangement schemes under twin-arc surfacing in a shielded environment, which leaves a scientific gap. The objective of this research is to evaluate the change in the geometric parameters of the reinforcement of the deposited layer and the morphology of the fusion zone with different relative positions of the electrodes under twin-arc surfacing in a shielded gas environment.Materials and Methods. The experiment was conducted on a 6-axis Fanuc 120iD robot with an EWM Titan XQ500 power source and an experimental surfacing head consisting of two welding torches. The layers were deposited on steel substrates of grade St3 using the GMAW Pulse method with Sv 08G2S wire with a diameter of 1.2 mm in an Ar/CO₂ environment (98%/2%) under a fixed surfacing mode (WFS = 6.5 m/min for each torch, TS = 4 mm/s, MW = 150°C). The following parameters were adopted as the studied factors: distances between electrodes (z = 15, 18, 21 mm), their angle of inclination (α = 5°, 10°). On the cross-sections of the deposited layers prepared by grinding and etching, the geometric parameters of reinforcement (height h, width S, wetting angle γ) and fusion penetration (depths a, a₁, width b) were measured. Quantitative analysis of the weld geometry was performed using Digimizer software to assess the effect of the relative position of the electrodes on the formation of the layer.Results. It has been found that the distance between the electrodes (z) affects significantly the reinforcement geometry: a growth of z causes an increase in the layer width (S) and the wetting angle (γ), but a decrease in its height (h). The axial fusion depth (a) demonstrated a nonlinear dependence on z, reaching a maximum (~2.2 mm) at z = 18 mm. The inclination angle (α) had a minor effect (<5%)on the reinforcement parameters, but affected significantly the shape of the main fusion zone (a₁): an increase in α decreased a₁ and made the penetration more gently sloping. At z = 21 mm, the impact of α on the penetration disappeared. The relationships between the relative positions of the electrodes under twin-arc surfacing, the geometric parameters of the reinforcement, and the depth of the fusion zone were specified.Discussion. The explanation of the established dependences is based on the change in the thermal and electrophysical properties of the electric arc depending on the mutual arrangement of the electrodes. The axial depth of fusion penetration depends not only on the distance between the electrodes, but also on the volume of the weld pool. With an excessive volume of the weld pool for a specific surfacing mode, a damping effect of heat flows from the electric arc to the base metal occurs — the volume of the weld pool absorbs part of the heat, which causes a decrease in the depth of penetration. The change in the arc pressure vector with an increase in the angle between the electrodes explains the decrease in the depth of the main fusion zone.Conclusion. The regularities of the effect of the mutual arrangement of electrodes on the geometry of the deposited layer and the shape of the fusion zone under twin-arc surfacing in a shielded gas have been experimentally established. It is shown that an increase in the distance between the electrodes results in an increase in the width of the bead, a decrease in its height, and an increase in the wetting angle. It has been noted that the penetration depth depends on the volume of the weld pool. It is determined that the angle of inclination of the electrodes in the studied modes has an insignificant effect — less than 5% — on the geometry of the deposited metal, although hypothetically, it can be enhanced at smaller interelectrode distances. The data obtained extract clear trends and form the basis for further in-depth study of the thermal and electrophysical aspects of the process of twin-arc surfacing in a shielded gas environment.

Due to its ability to fuse similar and dissimilar metals without melting and produce high-quality welds, friction stir welding (FSW) has become widely used in industry. This study presents a comparative analysis of the shear load performance of single-sided and double-sided FSW lap joints in AA2014 aluminium alloy. Friction stir lap welding, considered a potential alternative to conventional riveted joints, was carried out using reduced pin lengths to achieve partial thickness penetration and tapered weld geometry. Welding was performed on both sides of the joint under optimized process parameters to evaluate the influence of single- and double-sided FSW on shear strength. Experimental results showed that double-sided welded joints had a superior load-carrying capacity (52.8 kN) compared to single-sided joints (42.2 kN). The enhancement in shear performance is attributed to the refined and recrystallized grain structure formed on both sides of the weld zone. The findings highlight the effectiveness of double-sided FSW in improving the mechanical performance of AA2014 lap joints, making it a promising approach for aerospace and structural applications.

Abstract Micro friction stir spot welding (mFSSW) is one of the solid-state welding techniques developed to join thin plates with a thickness of less than or equal to 1000 µm. In this study, the effect of mFSSW process parameters on temperature, weld geometry, and tensile strength are investigated. The materials used were aluminum AA1100 and magnesium AZ31B with a thickness of 0.42 mm and 0.5 mm, respectively. The constant parameters of mFSSW were plunge rate of 4 mm/min and high tool rotational speed of 33,000 rpm. The other parameters were tool geometry (pin and pinless), plunge depth (400 and 600 µm), and dwell time (4 and 6 s). The results of this study show that the highest temperature, around 383°C, was at a plunge depth of 600 µm and a dwell time of 6 seconds using pinless tool. The lowest rotational speed, around 19,300 RPM, was at a plunge depth of 600 µm with a dwell time of 4 seconds using a pinless tool. The weld geometry results show that the weld shoulder diameter are close to the tool shoulder diameter when using a pin tool, while it exceeds the tool shoulder diameter when using a pinless tool. The maximum tensile shear load obtained is 370.41 ± 15.03 N using a pin tool at a plunge depth of 400 µm and a dwell time of 6 s. Joints produced using pinless tool exhibited weaker bonding, based on the macrostructure result.

Abstract This article presents the results of numerical investigations of T‐joints made of high‐strength square hollow sections under axial and bending loads. The work builds on the experimental results of FOSTA project P1504 by using detailed finite element modelling. These models were validated against test results and include a calibrated break‐off criterion that represents punching shear failure. Systematic parameter studies examined the effects of steel grade, the β‐ratio, chord wall thickness, weld geometry and chord pre‐stressing. The results confirm that, for β‐ratios between 0.4 and 0.7, the current Eurocode design rules (prEN 1993‐1‐8) are conservative, even without the material reduction factor Cf. However, for larger β‐ratios and thicker chord walls, the design rules tend to overestimate the load‐bearing capacity of the joints. For bending, tensile pre‐stressing improves resistance, which is underestimated by the current standard. The study suggests that adjusting the chord stress functions and including weld effects and effective width ratios could improve the accuracy and efficiency of designing joints for high‐strength hollow section structures.

ABSTRACT Emerging biomedical devices like implantable microsystems present new assembly and packaging challenges due to their miniaturization, complex integration, and diverse material combinations. Metals, glass, ceramics, and polymers are frequently used in biocompatible devices; reliably joining these dissimilar materials remains a critical concern. Researchers are working on different dissimilar combinations of metals to meet the growing demands of metallic biocompatible implants in the biomedical sector. The conventional adhesive bonding often fails to ensure long-term biocompatibility, it necessitates alternative joining techniques. Laser joining has emerged as a promising solution for achieving hermetic sealing, owing to its non-contact nature, localized heat input, and ability to preserve delicate biomedical components. Few studies are available on the joining of dissimilar metals, focusing on biomedical applications. The present study makes a comprehensive investigation of laser joining of titanium alloys to steel specifically for biomedical applications – an area with limited existing research. This study provides insight into the evolution of welding defects, strategies for their mitigation, and the underlying metallurgical transformations during laser joining. Special attention is given to how intermetallic phases form and spread at the interface, how they affect joint strength, and how they relate to laser process parameters. Furthermore, the review advances current understanding by systematically analyzing weld microstructure, geometry, and mechanical performance, addressing key gaps in existing literature. This review also highlights emerging trends, challenges, and future research directions for enabling more reliable and biocompatible joining of dissimilar materials for the future.