Typical Welding Research Articles

Physio-Mechanical Properties and Microstructural Characteristics of Friction Stir Welded Aluminium and Copper Plates Using Conical Unthreaded Tool

Friction Stir Welding (FSW) is a type of welding used to join materials for high strength applications. FSW is a well-liked solid-state welding technique for joining aluminum alloys and other non-ferrous materials in the aerospace, automotive, and marine industries. Pure copper and aluminum from the 6082 series were welded together using a specially designed milling machine. Tests for hardness, flexural rigidity, and impact are performed to assess the welding strength. Material flow and weld defects have been investigated by analyzing the microstructure of the weld junction. The modified vertical milling machine has been used to execute FSW of pure copper and aluminum plates. The aim is to explore the produced welded joints and to comprehend the difficulties encountered while utilizing milling machines as a FSW equipment. Similarly, to optimize the welding parameters in order to accomplish sound welding. FSW can be carried out on a milling machine because the flexural strength of a conical unthread thread tool is 108.58N/mm2 and 92.16N/mm2, respectively, at rotational speeds of 500 rpm and 1000 rpm with welding feed rates of 16 mm/min and 50 mm/min.

Efficient multi-branch dynamic fusion network for super-resolution of industrial component image

This work aims to promote the application of a high-performance super-resolution (SR) method in industry. Considering the lack of industrial datasets to evaluate performance, an industrial image SR dataset called WCI110 is first established, comprising 110 typical welding component images with 2040 × 1524 pixels. Subsequently, a parallel fusion structure of CNN and Transformer (FPFCT) is designed to achieve a high-quality reconstruction of component images. This model mainly contains the flexible parallel fusion (FPF) block and dynamic edge attention (DEA) network. The irreparable information loss caused by the inheritable sampling imperfection of CNN and Transformer can be effectively avoided by the parallel fusion structure in FPF block, while the contour features of multi-scale targets can be dynamically enhanced by DEA modules. The results show that the performance of FPFCT is higher than most advanced SR methods based on CNN, Transformer, or hybrid of CNN and Transformer. The images reconstructed by FPFCT are shown to help find and locate defects more effectively than other methods because its reconstructed target is closer to ground truth in terms of contour sharpness and size. Moreover, FPFCT achieves a remarkable advance in model parameters and time consumption, with a drop of more than 37.5 % in model parameters compared to the state-of-the-art SwinIR, and a reduction of more than 48.9 % in single-image delay time during reconstruction. The high efficiency of FPFCT makes it a promising image preprocessing tool for industrial images.

VARIATIONS IN MAGNETIC PROPERTIES PROPAGATION IN STEEL SHELL STRUCTURE CAUSED BY WELDING (PART 2)

The first stage of the research involves analyzing primary and secondary acoustic wave propagation behavior. The results of the first stage suggest that the properties of shell structures used at every stage of the experiment are distributed unevenly along the generator lines and across the width of the test pipes. In order to conduct a comparative study of properties, the authors of the research introduce the heterogeneity parameter. During the experiment, the parameter is changing locally within two orders of magnitude, even in case of test pipes in their initial state. Equal sensitivity to heterogeneities across steel products is found in its magnetic properties. As numerous studies prove, analyzing variations in magnetic properties makes it possible to detect flaws and areas of their concentration. This method can also be used to estimate the remaining service life. This is a crucial aspect to consider when assessing properties and using the findings to develop digital twins of shell structures. The authors focus on identifying acoustic and magnetic signals coming from flawed shell structures and weld joint areas in particular. For this purpose, magnetic memory method and X-ray analysis are used. It is found that both normal and tangential magnetic field components are sensitive to structural heterogeneities across a steel product. The combination of magnetic memory method and X-ray analysis make it possible to determine how typical weld joint flaws occurring during welding affect the magnetic properties. Sufficient measurements are required for statistical analysis of the findings. It is also possible to introduce further criteria in order to import metal properties correctly into the modelling program using numerical methods.

Fatigue Studies of Welded Stainless Steel 304L: Effect of Manufacturability and Weld Type, Choice of Fatigue Model, and Comparison to Pristine Material

Abstract This study investigates fatigue life and fracture in welded stainless steel 304L (SS 304L) resulting from load-controlled fatigue. This was done for specimens from two welding manufacturers. Mechanical testing was carried out using a MTS test frame in uniaxial tension. Specimens fabricated in 3 weld configurations (butt, lap, butt-with-backer) were cycled at stress ratio R = 0.1, frequency f = 5 Hz, and experienced varying mean tensile stress. A comparison of the fatigue life of welded and unwelded (or pristine) specimens determined that the fatigue life of welded specimens is considerably shorter. The microstructure in the parent material (PM), heat affected (HAZ) and fusion zones (FZ) was analyzed using SEM, and results suggest that, for a limited number of specimens (backer welds), fracture in the (FZ) was primarily the result of Zener-Stroh cracks. Most welded specimens fractured at the weld-HAZ interface (weld toe), and we postulate that stress concentrations primarily due to abrupt geometrical change at the weld interface led to crack initiation there. Additional stress concentrations at welding induced defects (resulting from high temperature) such as second phase particles, fatigue induced defects, and pre-existing impurities are responsible for crack initiation, crack growth, and eventual fracture. Comparison of unwelded and welded SN curve data using numerical curve fitting methods reveal that the fatigue life of pristine SS 304L follows the expected sigmoid shape found in literature (specifically the Chandran fatigue model), while that of welded SS 304L deviates considerably in low cycle fatigue (LCF) and follows the Basquin power law equation.

Dirençli Punta Kaynağı Prosesinin KNN ve CART Makine Öğrenimi Teknikleri ile Değerlendirilmesi

Spot welding, a type of resistance welding, is a welding application widely used in the production area and it is a common method for joining metal sheets. The spot-welding process is widely used in many production areas, especially in the automotive industry, radiator, and wire mesh production. Spot welding in car production lines is mainly performed by robotic applications. Industry 4.0 and digital transformation trends have led to unprecedented data growth. Nowadays, the manufacturing industry benefits from the power of machine learning and data science algorithms to monitor production processes and make predictions for quality, maintenance, and production optimization. Applying machine learning algorithms reduces the duration and cost of experiments. This study aims to confirm whether the spot welding, applied by robotic arms, is within the ideal spot-welding norms, in real production area. The ideal parameter norms were evaluated by using KNN and CART machine learning algorithms. To use real production data, this study was executed in the body production assembly line, which is selected as the pilot area, at TOFAŞ factory. The data set used in this research consists of the welding parameters of the current year, 2023. By running machine learning algorithms on the dataset, the performance evaluation of each algorithm was examined and the most appropriate estimation method was determined. In the experiments, the best F1-Score value was obtained by the CART model with 93%.

Experimental and numerical study on weld strengths of built-up steel box columns

This study investigates the demands generated in the panel zone of welded steel built-up box columns with fillet and complete joint penetration (CJP) groove welds, which are mainly used as columns in steel moment-resisting frames. The motivation for this study stems from the a 360–16 specification for structural steel building, which requires the joining of flange and web plates of box columns with CJP groove welds within a zone extending 12 in. above the upper beam flange and 12 in. below the lower beam flange in special and intermediate steel moment frames. Laboratory experiments have been conducted to examine the strength of these welds under pure shear forces. For this purpose, two laboratory specimens, one with fillet welds and the other with CJP groove welds, have been designed, and the strength of these welds were equal to each other in pure shear force conditions. The fillet weld specimen has resisted up to 1670 kN in the pure shear test, and the CJP groove weld has resisted up to 1520 kN. The entire loading process of each specimen was characterized by employing the digital image correlation (DIC) technique, which enabled the extraction of strain values throughout. Numerical modeling is validated in Abaqus software using experimental results, with comprehensive analyses on force-displacement diagrams and rupture. The outcomes of the tests conducted have shown that the demands generated in the panel zone of the built-up steel box welded sections are satisfactorily tolerated by both fillet and CJP groove welds. Research significanceThe significance of this study can be elaborated in multiple aspects. Firstly, it introduces an innovative test setup meticulously designed to replicate the behavior of welded built-up box columns with corner joints to steel plates. This advanced experimental arrangement not only facilitates the current study, but also serves as a versatile tool for conducting forthcoming experiments, allowing for meaningful comparisons and further exploration of diverse phenomena within the field. Secondly, the deliberate imposition of uniform demands on both types of welds during the study enables a comprehensive examination of their behavioral characteristics. This comprehensive analysis contributes to a more profound comprehension of welds performance under identical conditions, thereby enhancing our knowledge within the field. Finally, the research outcome, which reveals that fillet welds exhibit almost identical load-bearing capacity in comparison to CJP groove welds, bears substantial practical significance for the construction industry. This finding has the potential to instigate more cost-effective and efficient welding practices, which are paramount for maintaining the structural integrity of steel structures.In summary, this study makes a noteworthy contribution to the scientific community by presenting an innovative test setup, deepening the knowledge of weld performance, and suggesting practical enhancements in welding methodologies. These collective contributions serve to elevate the field of structural engineering, promoting advancements in construction practices.

Unified seam tracking algorithm via three-point weld representation for autonomous robotic welding

Autonomous robotic welding based on real-time seam tracking has shown excellent prospects in the field of intelligent manufacturing. In previous research, real-time seam tracking requires teaching trajectories, which has significant limitations. Moreover, as different types of welds have different shapes, their geometric distribution also exists in various forms such as straight lines, planar curves, and spatial curves, which brings significant challenges to the visual recognition of welds. The use of existing methods for tracking specific types of welds has limited applications. Currently, the existing methods are carried out for tracking specific types of welds, resulting in limited application scope. To handle various types of weld joints, a unified tracking paradigm named the three-point seam tracking algorithm (TSTA) is proposed in this study. First, a feature description method using three feature points is established to define different weld joints. The feature points are employed to reconstruct the position and attitude of welds, which allows the method to track welds of arbitrary geometries. Subsequently, a recognition method for the feature points combining morphology extraction and kernel correlation filter (KCF) tracker is designed. Combined with their respective advantages, the algorithm can identify the three feature points accurately and robustly in strong-noise environments. Extensive experiments including actual welding were conducted to verify the superiority of the proposed TSTA. Eleven representative types of weld seams were tested and all of them could be tracked in real time without any prior information. Compared with similar studies, the proposed recognition algorithm currently achieves the highest accuracy and best robustness. The TSTA provides a complete solution in autonomous robotic welding for unknown welds and shows excellent application prospects.

Weld size and resistance in rectangular hollow section T-joints

When chord face failure occurs, one of the factors, which influence the resistance of the square hollow sections joint is the brace-to-chord width ratio of the joint. This includes the size of the weld connecting the two members. The influence of weld type and weld size on the behaviour of rectangular and square hollow section joints was studied at the Czech Technical University in Prague.This paper describes an experimental and numerical investigation of square hollow section joints. The welded T-joints were loaded by axial compression. Three different types of welds were investigated - butt welds, fillet welds and a combination of these types. Experimental results for the T-joint together with material characteristics are provided. The paper presents a validation of the numerical model to experimental data. The research-oriented model with shell elements, prepared in RFEM finite element software, represents well the behaviour of square and rectangular hollow section joints. A parametric study with a broader range of sections was performed using the design-oriented shell elements model. Based on the results of the experimental and numerical investigations a modification of the analytical equations used in current prEN1993-1-8:2021 is proposed.

Analysis and design of column splicing flange joints with different weld types

To improve the seismic performance of steel column splicing flange joints, different weld details between the column and the flange plate were proposed in this study, and four full-scale specimens were designed and tested under cyclic loads. Finite element analysis was conducted to further check the joint performances and the weld behaviors. The hysteresis behaviors, yield moment, ductility, bolt forces, energy dissipation, stress and strains were analyzed. The parametric analysis, with finite element models validated by test results, was conducted, discussing the influences of the weld details, weld geometries and flange openings. According to the results, three of the four different weld details developed different advantages on ductility or energy dissipation capacity, bolt tension distribution, stress or strain distributions. Larger weld leg size would increase the resistance of the bolted flange splice joint, but may also cause weld residual stress and prying force. The reduction of flange opening can improve the stiffness and yield moments of the Type B flange joints. Formulas for the yield moments of the joints with recommended weld types were proposed and validated by both test and numerical analysis results, and additional formulas to check weld details were proposed for seismic design of bolted flange joints in prefabricated steel structures.

Research Progress and Prospects on Hydrogen Damage in Welds of Hydrogen-Blended Natural Gas Pipelines

Hydrogen energy represents a crucial pathway towards achieving carbon neutrality and is a pivotal facet of future strategic emerging industries. The safe and efficient transportation of hydrogen is a key link in the entire chain development of the hydrogen energy industry’s “production, storage, and transportation”. Mixing hydrogen into natural gas pipelines for transportation is the potential best way to achieve large-scale, long-distance, safe, and efficient hydrogen transportation. Welds are identified as the vulnerable points in natural gas pipelines, and compatibility between hydrogen-doped natural gas and existing pipeline welds is a critical technical challenge that affects the global-scale transportation of hydrogen energy. Therefore, this article systematically discusses the construction and weld characteristics of hydrogen-doped natural gas pipelines, the research status of hydrogen damage mechanism, and mechanical property strengthening methods of hydrogen-doped natural gas pipeline welds, and points out the future development direction of hydrogen damage mechanism research in hydrogen-doped natural gas pipeline welds. The research results show that: ① Currently, there is a need for comprehensive research on the degradation of mechanical properties in welds made from typical pipe materials on a global scale. It is imperative to systematically elucidate the mechanism of mechanical property degradation due to conventional and hydrogen-induced damage in welds of high-pressure hydrogen-doped natural gas pipelines worldwide. ② The deterioration of mechanical properties in welds of hydrogen-doped natural gas pipelines is influenced by various components, including hydrogen, carbon dioxide, and nitrogen. It is necessary to reveal the mechanism of mechanical property deterioration of pipeline welds under the joint participation of multiple damage mechanisms under multi-component gas conditions. ③ Establishing a fundamental database of mechanical properties for typical pipeline steel materials under hydrogen-doped natural gas conditions globally is imperative, to form a method for strengthening the mechanical properties of typical high-pressure hydrogen-doped natural gas pipeline welds. ④ It is essential to promptly develop relevant standards for hydrogen blending transportation, welding technology, as well as weld evaluation, testing, and repair procedures for natural gas pipelines.

Understanding the microstructural evolution and tensile characteristics of low nickel austenitic stainless-steel welds fabricated by diode LASER

In the present investigation, the utilization of diode laser welding in both continuous wave (CW) and pulse wave (PW) modes was applied to weld sections of 4 mm thick low nickel austenitic stainless steel (LNiASS) material. Subsequently, a comprehensive examination of the microstructural attributes of these welds was conducted by X-ray diffraction, electron backscatter diffraction (EBSD), and electron channeling contrast imaging (ECCI). The microstructural assessment was performed at both as-welded state and after the tensile deformation at three discrete strain rates ranging from 3.3 × 10−4 to 1.0 × 10−2. Furthermore, an investigation into the influence of strain rate variations on the tensile behavior of the two aforementioned types of welded joints, along with an exploration of the occurrence of strain-induced martensitic transformation, was carried out. The outcomes revealed that the PW welds yielded finer grain sizes in comparison to CW welds. It was observed that the martensite content within both CW and PW welds exhibited an augmentation with increasing strain rates. Furthermore, the PW welds exhibited a higher martensite content when compared to the CW welds under all examined strain rates. The PW welds consistently demonstrated higher UTS and total elongation across all three strain rates, while the CW welds exhibited a higher YS. Furthermore, as the strain rates increased, a decline in the strength ratio was observed for both weld types, accompanied by an increasing disparity between UTS and YS, indicative of work hardening phenomena.

ANALYSIS OF THE EFFECT OF CURRENT AND COOLING MEDIA IN TUNGSTEN INERT GAS (TIG) WELDING ON MECHANICAL STRENGTH AND MICRO STRUCTURE OF AISI 1045 STEEL FOR TRUSS FRAME MOTORCYCLE FRAME CONNECTIONS

AbstractCurrently, metal joining techniques in the field of welding have developed rapidly. In constructions that use metal raw materials, most of the joints are made by welding. Apart from joining, the welding process can also be used for repairs, for example to fill holes in castings, make coatings on tools, thicken worn parts and other repairs. Welding is also widely used for building construction, bridges, piping and automotive. As we know, there are many types of welding used today. One of them is Gas Tungsten Arc Welding (GTAW) or commonly called Tungsten Inert Gas (TIG).AISI 1045 steel is referred to as carbon steel because it complies with international coding, namely the 10xx series based on the nomenclature issued by AISI and SAE (Society of Automotive Engineers). The first number 10 is the code that indicates plain carbon, then the code xxx after the number 10 indicates the carbon composition. So AISI 1045 steel means carbon steel or plain carbon steel which has a carbon composition of 0.45%. Steel of this specification is widely used as a component of gears, shafts and bearings. According to its function, it must be able to withstand wear and tear due to friction with the chain. Wear resistance is defined as resistance to abrasion or resistance to dimension reduction due to friction

Tensile efficiency and fatigue life of similar and dissimilar carbon steel joints subjected to rotary friction welding

Rotary friction welding (RFW) is a solid-state welding method that can address the melting point limitation of other welding types; however, the welded area remains at risk of failure due to fatigue during operation. Fatigue failure is difficult to detect and predict, making it a critical failure mode in engineering. Although many fatigue life prediction methods are available, they do not consider the impact of RFW parameters (such as pressure, speed, and friction time) on fatigue strength. Owing to their good mechanical properties and commercial viability, carbon steel of grades C35 and C45 is commonly applied to manufacture main parts in the automotive industry. This study centers on employing RFW to join C35 and C45, representing the first-ever instance of using this technique to weld them together. The primary goal of RFW for C35 and C45 is to construct optimum parts that meet specific design requirements and have a long fatigue life. Findings showed C45–C45 joints (77 %) were more tensile-efficient than C35–C35 joints (73 %). Dissimilar C35–C45 joints reached 60 % of C45 base metal and 76 % of C35 base metal in terms of tensile efficiency. RFW welds had lower tensile strength than their base metals. Optimal results came at 35 MPa friction pressure and 8–12 s friction time for both similar and dissimilar RFW joints using the Coffin–Manson method, dissimilar C33–C45 joint fatigue life improved by over 85 %, aligning C35 and C45 engineering aspects. SEM microstructure analysis showed two regions: non-deformed (NDZ) and plastically deformed (PDZ), with broader PDZ indicating better tensile strength. These findings enhance RFW's efficiency, promoting automotive part longevity and safety.

New possibilities for laser welding of highly loaded transmission components by strategic use of simulation methods

Laser welding in transmission manufacturing opens up completely new kinds of product solutions with excellent properties in terms of wear, corrosion resistance, and service life. Current welding designs are characterized in particular by difficult-to-weld material combinations (e.g., steel versus cast iron) and a high component stiffness, which is correlated with high residual welding stresses. The major challenge for these mass-produced components remains both their crack-free weldability and their complex cyclic load capacity [U. Stamm, “Rissfreies Laserstrahlschweißen von Mischverbindungen aus Gusseisen und Einsatzstahl, Jahresbericht Fraunhofer IWS 2006” (2006); X. Shu, “Untersuchungen zum Laserstrahlschweißen von Werkstoffkombinationen aus Gußeisen und Stahl,” Dissertation, Shaker, Band 4/94 (1994), ISBN: 3-8265-0098-9; G. Göbel, “Erweiterung der Prozessgrenzen beim Laserstrahlschweißen heißrissgefährdeter Werkstoffe,” Dissertation, Fraunhofer-IRB-Verlag (2007), ISBN: 978-3-8167-7671-0]. Therefore, this contribution presents practical solutions for weld-compatible joint constructions and the reduction of residual stresses on the basis of a representative transmission design. Specifically, a systematic study is being conducted to understand and qualitatively evaluate effective methods for reducing residual weld stresses in circumferential welds. The recommendations developed as part of this study take particular account of the influence of process modifications, material conditions, and geometric aspects on weldability and component distortion. Here, structural welding simulations are performed and verified by experimental welding trials, including metallographic examinations. To ensure the required component fatigue strength, a practical concept for determining Wöhler curves is presented, which is based on structural mechanical simulations and multiaxial fatigue strength tests on simplified test specimens. The adaptations developed in this way facilitate the production of difficult-to-weld and highly stressed transmission components. In particular, time-consuming and cost-intensive iterations of laser welding tests can be significantly reduced or even eliminated [Brenner et al., “Neuere Ergebnisse zum Schweißen von Eisenbasiswerkstoffen mit Faserlasern, 5. Laser-Anwenderforum,” Strahltechnik Band 28 (2006), pp. 139–148, ISBN: 3-933762-18-9, S]. Furthermore, the systematic investigations provide effective recommendations for phenomenological understanding and solving typical welding challenges in practice [J. Standfuß, “Ganzheitliche innovative fügetechnische Konzepte am Beispiel des PKW-Antriebsstranges,” Fraunhofer Verlag (2010), ISBN: 978-3-8396-0125-9]. This applies, in particular, to load-transmitting components in the fields of e-mobility, aerospace, and industrial engineering [Wagner et al., “Entwickeln und Auslegen von lasergeschweißten Getriebe-komponenten für die Luftfahrt,” DVS-Berichte Band 365 (2020), pp. 62–69, ISBN: 978-3-96144-098-6].

ANALYSIS OF SMAW IN DIFFERENT MATERIALS WITH ELECTRODE VARIATIONS

Welding is a technique for joining metals by melting part of the parent metal and filler metal with or without additional metal and producing a continuous connection. One type of welding that is often used is SMAW welding (Shield Metal Arc Welding). In SMAW welding, the influence of the electrode strength or amperage used plays an important role in welding, because it influences the results of the joint strength during welding. Therefore, the current setting must be appropriate to the material and choosing the right welding parameters will also improve the quality of the welding results. This research was conducted to determine the mechanical properties of tensile testing and the microstructure of the influence of the different electrodes and amperes that will be used. In this research, current variations of 70 A, 80 A, and 90 A were used and the types of electrodes used were E6013, E309-16 and E7018. The research results obtained from the tensile test had an optimum value for the E7018 electrode, 90 A with a tensile strength of 41 .60 kg/mm. The tensile test results for E7018 obtained an average tensile value of 33.19 kg/mm. The tensile test result value of E6013, 80 ampere has a value of 36.55 kg/mm, after being averaged the tensile strength of E6013 is 35.36 kg/mm, the tensile test result of E309, 80 A has a value of 38.15 kg/mm after being averaged got a tensile test value of 36.20 kg/mm.

Predicting the weld zones size in FSSW of 304L stainless steel plates by mathematical model based on RSM

The 300 series austenitic stainless steels are widely used in industries due to their special properties. High heat in fusion welding reduces the properties of these steels and causes many problems. Therefore, stir friction spot welding, which is a type of solid state welding, is useful and widely used in high-tech industries. In this paper, a 3D dynamic explicit finite element model is developed to simulate the friction stir spot welding of 304L stainless steel plates. Using this model, the temperature distribution and the size of weld zones (thickness of weld zones) are obtained. Then, by experimental study, the results of the temperature and the size of weld zones were obtained to be a criterion for comparing and validating the numerical results. Microstructure and hardness of these zones are determined experimentally. Finally, a mathematical model based on the response surface methodology is proposed to predict the size of weld zones. Good agreement between the numerical results that are produced by the finite element simulation, the proposed model and the experimental data is observed. The results show the maximum temperature level appears in the stir zone and it reduces by moving from the weld center. Also, by increasing the rotational speed, plunging depth and dwell time of the tool, the size of both the stir zone and the heat affected zone increase to a peak value and then the size of the latter zone decreases.

Dissimilar welding of UNS S31803 and UNS S30400 tubes superiority and adverse in rotary friction welding

Solid-state welding provides a distinct state of the art to joining various metal tubes. In contrast to other types of welding, dissimilar joining by solid-state welding maintains the integrity of its joints. Dissimilar joints of UNS S31803 and UNS S30400 tubes were carried out using rotary friction welding process. Three combinations of tube joints fabricated were, ASS to ASS, DSS to DSS and ASS to DSS joint. The tensile tests showed dissimilar weld joint achieved the minimum strength of ASS similar joint. Fractography for similar and dissimilar tube joints showed a ductile pattern of fracture with dimples and voids in the dissimilar tube weld. Microstructure analysis showed that diffusion bond line for similar and dissimilar joints confirms the sound weld tube joints. Corrosion test showed that among three combinations, ASS to DSS dissimilar joint had lesser corrosion rate than ASS to ASS or DSS to DSS similar joints.

Achieving superplastic TWIP steel welded joint via vacuum electron beam welding

A crack-free high-Mn TWIP steel welding joint with comparable strength and superplastic was obtained via vacuum electron beam welding (VEBW) where the microstructural evolution, mechanical behaviors and strengthening mechanism of welding joint were investigated. The results indicated that the welding joint with a typical nail-shaped welding cross-section was divided into three zones including the base metal (BM), heat-affected zone (HAZ) and fusion zone (FZ). Massive fine AlN-type precipitates with the hexagonal crystal structure were observed in welding join. The orientation relationship between the γ-austenite matrix and AlN precipitates was determined as [001]γ//[2110]AlN. In FZ, small-sized cellular grains or columnar grains with consistent growth directions were combined into large-sized columnar grains with obvious <001> preferential orientation. Compared with the base mantal, the yield strength, ultimate strength and elongation of the VEBWed specimen were slightly reduced by 6.03%, 4.7% and 13.23%, respectively. However, the impact toughness was obviously decreased from the 87.90 J–68.97 J after the VEBW process, which was mainly attributed to the brittle AlN precipitates, inhomogeneous microstructure and back stress induced by the plastic mismatch between gradient grains. The strength contributions of different regions to overall strength including of BM, HAZ and FZ in welding joint were calculated. Here, the dislocation strengthening and precipitation strengthening were the dominant strengthening mechanisms of FZ, which was attributed to the high level of density and massive fine AlN precipitates induced by micro-elements segregations during the VEBW process.

Discussion on Fatigue Reliability Evaluation Method of Welded Structure of Carbody Based on Digital Twin

Abstract Taking the key welds of the heavy-duty gondola carbody as the research object, first, the fatigue assessment of the carbody is carried out based on the quasi-static the main S–N curve method, and the quasi-static evaluation method is discussed; second, the typical welds are selected. Based on the full-size bench physical test and virtual test of railway freight carbody, the quasi-static method is discussed; finally, the line test is used to verify the results. The results show that: (1) among all the load conditions in the quasi-static analysis of railway freight cars, the damage of the core plate needs to be considered according to different parts of the carbody, and this condition is effective for the evaluation of the bearing area of the linear load transfer of the carbody for the welds with nonlinear load transfer such as floor, the stress response caused by core plate load has the problem of over-estimation of damage. (2) The lap weld of floor and beam is less damaged under heavy load, but the stress response is larger in empty state, which indicates that the vibration effect should be considered in the design. (3) The virtual test can make up for the problem of traditional quasi-static analysis. The combination of the two can better realize the fatigue reliability evaluation of carbody.

Influence of fusion welding processes on microstructure and mechanical properties of dissimilar metal (AISI 304 SS-Copper) weldment

Dissimilar metal welding of AISI 304 stainless steel (304 SS) and commercially pure copper (CP copper) has been taken up to understand the influence of the different fusion welding processes on microstructure and mechanical properties of the weldment. The fusion welding processes specifically involve continuous wave CO2 laser, pulsed wave Nd: YAG laser and pulsed wave tungsten inert gas (P-TIG) welding. The primary objective of the present work is to develop a successful weld between two dissimilar metals without using any filler material by different fusion welding processes. An overall comparison of the results obtained from different sets of analyses is represented. The optical image of the top surface of the weld revealed that the no spatter formation during CO2 laser and P-TIG welding process, whereas minimal spatter for Nd: YAG laser. In comparison to laser processes, the weld face formed by P-TIG welding was much wider. However, 100 % penetration was achieved with all three types of welding. The average widths of heat affected zone (HAZ) found to be 10 µm and 23 µm for CO2 and Nd:YAG laser respectively. The way the microstructure changes at the fusion zone was the same in all cases. For example, copper channels form, dendrites grow epitaxially, etc. SEM pictures indicate the Cu tubular channels observed more often for P-TIG welding. The microhardness distribution in the weld zone was found to be larger than that of copper and close to that of 304 SS. The acceptable ultimate tensile stress (UTS) for dissimilar metal welding of SS-Cu couples was found 275 MPa, 278 MPa and 195 MPa for CO2 laser, P-TIG and Nd:YAG laser respectively.