Search Results (2,603)

Welded joints are widely recognized as the most critical point in structures made of armour steels due to pronounced thermal effects, microstructural heterogeneity, and the degradation of mechanical and fatigue properties. This study investigates the mechanical properties and fatigue crack growth resistance of a welded joint produced on SA 500 armour steel, with the aim of preserving the properties of the base material as much as possible. To achieve this, a welding procedure incorporating a high-strength filler wire and optimized welding parameters was applied. Hardness and tensile testing was conducted to evaluate the extent of property degradation caused by welding. The results demonstrate that the applied welding process effectively limited the reduction in hardness and tensile strength, achieving values reasonably close to those of the base material. In addition, fatigue crack growth behaviour was investigated in accordance with ASTM E647, using both the Paris law and the McEvily law. The obtained fatigue crack growth curves and threshold stress intensity factor (ΔK_th) values indicate the nearly identical fatigue behaviour of the base material and the heat-affected zone, confirming the successful preservation of base material fatigue behaviour in the thermally affected zone. Moreover, the weld metal exhibited superior resistance to fatigue crack initiation and growth. Overall, the results confirm that the proposed welding approach provides favourable mechanical and fatigue performance for welded joints in armour steel applications. Full article

The production of fiber-reinforced polymer composites using 3D printing technology offers significant potential and opportunities for industrial applications. However, current dimensional limitations in 3D printing necessitate the use of joining techniques to obtain larger components. Recently, innovative strategies such as friction stir spot welding (FSSW) have attracted considerable attention for joining polymer composites due to their ability to produce strong joints with relatively low heat input (solid-state welding). Nevertheless, it is important to understand how the fibers present in fiber-reinforced polymer composites influence material flow and welding performance during the FSSW process. In this study, glass fiber-reinforced polylactic acid (PLA-GF) composite samples produced using a 3D printer were joined by means of FSSW. Five different tool rotational speeds (900, 1200, 1500, 1800, and 2100 rpm) and three different plunge rates (10, 20, and 30 mm/min) were employed during the welding process. Mechanical tests were performed on the welded joints to investigate the relationship between the welding parameters and the resulting mechanical properties. In addition, microstructural analyses were conducted to examine the formation of welding defects. The results revealed that three distinct zones were formed in the material after the FSSW process: the stir zone, mixed zone, and shoulder zone. Defects were observed in the mixed zone of the samples exhibiting relatively lower mechanical properties. The highest tensile force was achieved at a plunge rate of 20 mm/min and a rotational speed of 900 rpm. The highest bending force, on the other hand, was obtained at a plunge rate of 30 mm/min and a tool rotational speed of 2100 rpm. Full article

In this study, the microstructure and mechanical properties of ultrasonic welded joints between large-diameter aluminum wire and Cu (Ni-plated copper) terminals were systematically investigated, to reveal the underlying fracture mechanisms. The cross-sectional morphology, interfacial microstructure, and mechanical properties of the two types of welded joints are investigated. The results indicate that ultrasonic welding produces well-structured Al-Cu and Al-Ni joints. Under the same welding process parameters, the Al-Cu joint exhibits many pores, while the Al-Ni joint has no pores in its microstructure. The interfacial region of the Al-Cu joint presents various morphologies, such as flat bonding, interlocking, and eddy current patterns, whereas the Al-Ni joint interface is flat. No significant atomic diffusion phenomenon occurs between the interfaces of the two types of joints. The tensile strength of the Al-Cu joint is 53 MPa, with fracture modes including ductile fracture and brittle fracture, whereas the tensile strength of the Al-Ni joint is 50 MPa, with a failure mode of pull-out fracture. In working conditions requiring ultrasonic welding of aluminum and copper, nickel-plated copper can be used as a substitute for copper to prevent electrochemical corrosion between aluminum and copper. Full article

In order to verify the feasibility of in situ repair of underwater local dry laser welding (ULDLW) on nuclear power reactor components, this work investigates the microstructure and mechanical properties of 304L austenitic stainless steel repaired by ULDLW using ER308L filler metal. Comprehensive comparison would be made between the ULDLW and conventional in-air laser welding to evaluate their applicability. The results demonstrate that the rapid cooling rate inherent to the underwater environment significantly influences solidification behavior and microstructural evolution. The weld metal (WM) solidifies in the ferritic–austenitic (FA) mode, with an increased proportion of lathy δ-ferrite at the expense of skeletal morphology compared to the in-air welds. Electron backscatter diffraction (EBSD) analysis reveals the substantial grain refinement in underwater welds, with average grain sizes of 39.4 μm versus 47.3 μm for in-air weld bead, accompanied by a higher fraction of low-angle grain boundaries (LAGBs). These microstructural modifications yield superior mechanical properties: underwater weld bead exhibits ultimate tensile strength (UTS) of 685.6 MPa, elongation of 57.5%, and impact toughness of 22.6 J, significantly exceeding the corresponding values for in-air welds (663.9 MPa, 51.8%, and 18.6 J, respectively). Fractographic analysis confirms ductile fracture mechanisms in both conditions. The enhanced performance is attributed to grain refinement strengthening via the Hall–Petch relationship and the increased LAGBs fraction, which impedes dislocation motion and crack propagation. Full article

Residual stress is an inherent consequence of the welding process and can significantly compromise the structural integrity of welded components. To clarify the high-temperature creep damage evolution of the 600 MPa-grade ship hull structural steel base metal, high-temperature creep tests were conducted, aiming to improve the understanding of its deformation behavior and to support reliable numerical predictions. The experimentally calibrated creep constitutive model was subsequently integrated into finite element simulations to analyze the residual stress evolution in welded joints and to quantitatively evaluate the effects of post-weld heat treatment (PWHT) and hammer peening. The results indicted that, within 450–550 °C, creep deformation of the steel was dominated by dislocation glide and climb, while creep damage was mainly associated with void and crack formation. The simulation results revealed that residual stresses were predominantly concentrated in the weld metal and the heat-affected zone, with the peak von Mises stress in the as-welded joint reaching 686.5 MPa, exceeding the material’s yield strength at the simulated temperature. PWHT exhibited superior stress-relief effectiveness compared with hammer peening, markedly reducing the peak residual stress. Moreover, the stress-relief behavior showed a nonlinear dependence on both holding time and heat-treatment temperature. In contrast, hammer peening produced a localized stress-relief effect, confined primarily to the mechanically impacted region. These findings provided a theoretical foundation for optimizing post-weld treatment strategies to mitigate residual stress in the high strength steel welded joints. Full article

This study evaluates the mechanical performance of FDM-printed poly(lactic acid) (PLA) structures joined using a portable Friction Stir Welding (FSW) device. A non-destructive optical band method was employed to assess weld homogeneity and material flow consistency. The influence of substrate infill density (15% and 100%) and tool pin geometry (cylindrical and truncated conical) was systematically analyzed. Results indicate that substrate density is the primary determinant of joint integrity; 100% infill specimens demonstrated superior structural homogeneity and consistent intensity profiles, whereas 15% infill specimens exhibited significant intensity fluctuations and poor consolidation, even with the addition of filler material. The mechanical evaluation revealed that the use of a tool pin is essential for effective load transfer, as specimens welded without internal agitation achieved only baseline tensile strengths of approximately 4 MPa. Among the pin-driven configurations, the cylindrical geometry outperformed the truncated conical design, reaching a peak tensile stress of 8.02 ± 1.42 MPa, corresponding to a joint efficiency of 27% relative to the 100% infill base material, compared to 6.25 ± 1.43 MPa. This performance gap is attributed to the cylindrical pin’s ability to maintain higher shear rates and more uniform pressure distribution at the weld root. These findings demonstrate the feasibility of portable FSW for structural joining of additively manufactured polymers and establish critical processing parameters for the optimization of portable FSW in engineering applications. Full article

To solve the problems of poor weld formation, difficult slag removal, and inferior joint microstructure and hardness in conventional narrow-gap submerged arc welding (NG-SAW), a swing arc NG-SAW process assisted by pre-embedding cold wires was proposed. Synergistically optimizing the welding energy parameters and additional cold wires ensured sound weld formation and enhanced slag detachability, while the efficiency of multilayer welding was improved by reducing the number of weld layers by 33.3%. The slag adhesion mechanism is clarified as follows: a high welding heat input facilitates elemental diffusion at the weld–slag interface, leading to the formation of a continuous and thick interlayer composed of (Fe,Mn)O and MgO-Al₂O₃-CaO phases. This interlayer strengthens the chemical bonding between slag and weld, thereby impeding slag removal. Microstructure evolution analysis of the multilayer welded joint revealed that the variable-angle design increases the groove volume and, combined with the heat-absorbing effect of the additional wires, accelerates molten pool cooling, thereby refining grains in both the weld metal zone and reheat-affected zone. Meanwhile, the tempering exerted by the heat-affected zone (HAZ) of the subsequent weld layer on the previous layer is attenuated. This promotes the gradual transformation of hard-brittle lath martensite in the coarse-grained heat-affected zone (CGHAZ) of the bottom layer into tougher tempered martensite/bainite in the CGHAZ of the upper layers. As a result, the hardness uniformity within the HAZ, the critical weak region of the joint, was enhanced by 54%, enabling synchronous improvement in microstructural homogeneity, hardness distribution, and overall welding efficiency. Full article

To precisely evaluate the fatigue hot-spot stress concentration factor (SCF) of welded tubular joints and verify the accuracy of existing methods, this research selects Y-type tubular joints as the research subject. The dihedral angle formula is re-derived, and the dihedral angles corresponding to each polar angle along the intersection line are calculated using MATLAB R2018a (MathWorks Inc., Natick, MA, USA). After determining the geometric parameters of the weld profile in accordance with AWS specifications, finite element models named “AWS-max” and “AWS-min” are established in ANSYS 2022 R1 (ANSYS Inc., Canonsburg, PA, USA). These models meet the maximum and minimum allowable weld sizes respectively, and a novel modeling approach is proposed. Tests on tubular joints under axial tension loading are conducted, and the SCF is obtained through the surface stress interpolation method. Comparative analyses are carried out among the SCF from the established “AWS-max” and “AWS-min” weld models, the non-weld model, and the test results of the tubular joints. The results indicate that the weld geometric size has a significant impact on SCF: a larger weld cross-section results in a lower SCF. For the AWS maximum weld model, the SCF of the chord ranges from 4.21 to 5.42, and that of the brace ranges from 1.71 to 5.33; for the AWS minimum weld model, the chord SCF is 4.41–5.73, and the brace SCF is 2.11–5.79. The numerical results are in good accordance with the experimental data, while the non-weld model produces obviously conservative results with inconsistent distribution laws. The calculated dihedral angles obtained by the proposed method are highly consistent with the AWS standard. The modeling method is characterized by reliable accuracy and strong engineering applicability, and can be extended to the SCF calculation and fatigue evaluation of various tubular joints. Full article

Traditionally, the calibration of welding heat source model parameters mainly relies on empirical trial-and-error methods, which lack clear guidance and generally lead to low computational efficiency. To address this problem, this paper establishes a quantitative relationship between heat source parameters and weld pool dimensions, which significantly improves the efficiency and accuracy of the simulation. Furthermore, the influence of laws of key parameters of the double-ellipsoid heat source and welding thermal efficiency on the geometric characteristics of the weld pool is systematically analyzed via numerical simulation. On this basis, finite element models considering different welding sequences are established for single and multiple T-rib components, and appropriate welding process parameters are determined according to the influence laws of heat source parameters. The thermo-elastic–plastic finite element method is then adopted to analyze the effects of welding sequences on the welding residual stress and deformation of T-rib and top-plate joints in steel box girders. By comparing different welding schemes, optimized welding strategies for single and multi-rib welding are proposed. The results show that for single T-ribs, simultaneous welding in the same direction produces the minimum residual stress and deformation with almost no distortion, followed by sequential bilateral welding in the same direction. For multi-rib welding with a spacing of 300 mm, synchronous welding yields the smallest deformation, followed by symmetric double-pass synchronous welding from inside to outside. For continuous single-pass welding, an inside-to-outside skip welding sequence is recommended to effectively control residual stress and deformation. Full article

The structural integrity of bogie frames is a critical factor in the safety and reliability of railway rolling stock, requiring advanced assessment methods to handle complex, multi-axial stress states. This research presents a robust numerical framework for the preliminary fatigue evaluation of a metro bogie frame, integrating high-fidelity Finite Element Analysis (FEA) with the Findley multi-axial fatigue criterion. The methodology overcomes the limitations of traditional uniaxial verification methods by employing a localized critical plane approach, implemented through a proprietary computational code. The investigation simulates a realistic operational scenario by superimposing a static vertical load of 15 tons per side with dynamic components derived from on-track accelerometric data. This integrated loading condition enables a precise reproduction of the “rotating” stress states typically encountered in service. Global structural analysis identified critical transverse welded joints as high-stress concentration zones, which were then subjected to a detailed multi-axial investigation. By correlating the extracted stress tensors with the resistance category included in the reference standard, over a regulatory life of 10 million cycles, a maximum cumulative damage index of 0.4602 was recorded. The results demonstrate that while the frame possesses adequate structural reserves, nearly half of its fatigue life is consumed in localized nodes. This methodology provides a reliable and computationally efficient tool for the structural health monitoring and development of innovative railway geometries, offering a superior predictive capability that remains scarcely utilized by major rolling stock manufacturers. Full article

In this work, the focus is laid on the mean stress effect on the fatigue strength of thin-walled rectangular hollow section T-joints made of high-strength steel S960 M x-treme. The specimens are cyclically tested at a stress ratio of R = −1 and R = 0.1 in both as-welded and ground (weld-profiled) conditions. In the context of nominal stress evaluations, the ground specimens demonstrate a distinct advantage in contrast to the as-welded condition, exhibiting an increase of +33% at R = 0.1 and +16% at R = −1. Based on the experimental results, a corresponding Haigh diagram is evaluated, revealing a notable difference in the mean stress sensitivity, with M₁ = 0.58 for the as-welded condition and M₁ = 0.39 for the ground condition. Finally, mean stress factors are presented, enabling feasible application in the fatigue design of welded and post-treated structures. The resulting factors are compared with values from the literature for steel applications, showing an increased mean stress influence using high-strength steel as the base material. Full article

The growing need for lightweight, multifunctional, and high-performance structures in the automotive, aerospace, electronics, and medical industries has driven the development of advanced joining technologies for polymers and metal-polymer combinations. Among these, ultrasonic welding (USW) and friction stir spot welding (FSSW) have emerged as promising solid-state techniques capable of producing reliable joints with minimal thermal degradation and enhanced interfacial bonding. This review focuses on recent developments in USW and FSSW of thermoplastics, fiber-reinforced composites, and hybrid metal–polymer systems, with a particular emphasis on process mechanics, microstructural evolution, and joint performance. The mechanisms of heat generation, material flow behavior, and consolidation are discussed in relation to key process parameters, including applied pressure, rotational speed, vibration amplitude, plunge depth, and dwell time. Microstructural transformations such as polymer chain orientation, recrystallization, interfacial diffusion, and defect formation are analyzed to establish process–structure–property relationships. Mechanical performance metrics, including lap shear strength, fatigue resistance, impact behavior, and environmental durability, are critically compared across different materials and welding methods. Furthermore, recent advances in numerical and thermo-mechanical modeling, in situ process monitoring, and data-driven optimization are discussed to highlight pathways toward predictive and scalable manufacturing. Current industrial applications and existing limitations such as challenges in automation, thickness constraints, and hybrid material compatibility are also evaluated. Finally, key research gaps and future directions are identified to improve joint reliability, sustainability, and broader industrial adoption of advanced solid-state welding technologies. Full article

As a solid-state welding technique, friction stir welding (FSW) has many advantages over conventional fusion welding. Its applications in the manufacturing and joining of parts in aerospace, automotive, and shipbuilding have significantly increased. Friction heat generation is the fundamental driver of the FSW process. It governs material flow, microstructural evolution, mechanical properties, and residual stresses. Understanding the effect of heat generated on the joint quality is essential for process parameter optimization, ensuring defect-free welds and high-quality joints. Thus, evaluating the thermal history of the FSW process is a key requirement for effective analysis. This comprehensive review critically discusses research studies published over the past three decades (1991–2025) that have examined different approaches to predict and measure heat generation in FSW. A total of 136 highly relevant articles were selected from the Scopus database and systematically analyzed. The effects of various welding parameters on heat generation, microstructural evolution, and joints’ mechanical properties have been reported. Different heat generation prediction and measurement techniques, such as analytical models, finite element models (FEM), and experimental methods have been discussed in terms of their feasibility, accuracy, advantages, disadvantages, and cost. The evolution, state of the art of analytical models and FEM over the last three decades are analyzed and future research directions are outlined. Finally, the correlation between process parameters, heat generated, microstructural development, and mechanical performance of the welded joints for various workpiece materials is investigated. This review provides a critical and comparative perspective that highlights the strengths and limitations of each method, offering practical guidance for researchers and industry practitioners. Full article

This study compares the microstructural evolution and mechanical properties of TC4 (Ti-6Al-4V) titanium alloy joints welded by Tungsten Inert Gas (TIG) and laser processes, following a post-weld annealing treatment at 650 °C for 2 h. Distinct microstructures were obtained: the TIG-welded joint developed a heterogeneous mixture of short-rod α and lamellar β, while the laser-welded joint formed a more homogeneous equiaxed α structure with uniformly distributed β-phase nanoparticles. Electron backscatter diffraction (EBSD) results confirmed that the annealing treatment significantly weakened the strong welding-induced texture and disrupted the epitaxial growth mode of columnar grains. Mechanical testing demonstrated that annealing improved the strength-toughness balance, but the extent and mechanism differed between the two processes. For the TIG-welded joint, the ultimate tensile strength slightly decreased, while elongation and impact toughness increased by 18% and 10.4%, respectively. In contrast, the laser-welded joint maintained its original strength while achieving greater improvements in ductility and toughness, with elongation and impact toughness increasing by 20% and 15.2%, respectively. This divergence is attributed to insufficient recrystallization and the persistence of residual coarse grains, limiting the TIG joint’s performance. However, in the laser-welded joint, the pinning effect of β-phase nanoparticles and associated grain refinement enhanced ductility without compromising strength. Full article

The quality of underwater laser welds is strongly dependent on the flow rates of the shielding and drainage gases. This study investigated the effect of argon and drainage gas flow rates on the formation, microstructure and mechanical properties of 304NG stainless steel using local dry underwater laser welding. At a water depth of 100 mm, with a laser power of 3.0 kW and a welding speed of 8 mm/s, the optimal conditions within the tested range were a shielding gas flow rate of 30 L/min and a drainage gas flow rate of 80 L/min. These conditions produced a continuous weld bead with an attractive surface and yielded the highest average maximum tensile load of 4.31 kN. Metallographic observations revealed that the weld metal primarily consisted of austenite alongside skeletal and lamellar ferrite, while the hardness along the weld depth remained relatively consistent at around 180 HV. These results demonstrate that matching the flow rates of the shielding and drainage gases properly is essential for stabilising the local dry cavity and improving weld quality and joint performance. Full article