Welding in the World最新文献

Analysis of mechanical properties of welded joints considering material and geometric inhomogeneity helps to improve the accuracy of joint performance prediction. The influence of material and geometric inhomogeneity on the mechanical properties of welded joints, encompassing stress–strain behavior, microstructural characteristics, and hardness profiles, was investigated. The present study focuses on the aluminum alloy oscillating laser welded (OLW) joint and employs response surface method and entropy weight method to establish an approximate model, thereby determining the optimal welding parameters. Subsequently, the stress–strain characteristics and microstructure of the weld (WM), base metal (BM), and heat-affected zone (HAZ) were obtained. To characterize the overall stress–strain characteristics of welded joints, three equivalent meso-damage model methods based on the Gurson-Tvergaard-Needleman (GTN) model were proposed, and the advantages and disadvantages of the methods were comprehensively evaluated by comparing the accuracy and efficiency of joint performance prediction. In addition, the stress–strain simulation analysis of the joint’s sub-region was performed to verify the effectiveness of the three-material equivalent model method in predicting the performance of the welded joint sub-region. Built on the study contents discussed above, the equivalent meso-damage model suggested in this paper completely accounts for the joint’s inhomogeneity and can accomplish high-precision prediction of the joint’s overall and local performance.

Novel generations of shipbuilding steels have outstanding toughness due to the improved steel producing processes. Their microstructure mainly consists of ferrite and bainite, while the presence of acicular ferrite has a role in high impact energy of the welded joint. This research aims to analyze the effect of multipass welding on weld characteristics of S500 shipbuilding steel. A Gleeble 3500 simulator machine is used to produce the welding thermal cycles by the Rykalin-3D model on 70 (times) 10 (times) 10 mm samples manufactured in transversal direction from a submerged arc welded joint of 16 mm plate. Temperatures for the simulations were set at 1350 °C for the coarse-grained zone forming in the weld metal (CGHAZ-W), 815 °C for the intercritical zone (ICHAZ-W), and a combination of these peak temperatures for the intercritically reheated coarse-grained zone (ICCGHAZ-W). The examined t_8/5 interval was 5–30 s. The weld properties were examined by microstructural examination, hardness test, and instrumented Charpy V-notch impact toughness test. The impact energy values of subzones were below the unaffected weld metal. Longer cooling time resulted in lower impact energy in ICHAZ-W. However, this tendency was not observed in CGHAZ-W. ICHAZ-W and ICCGHAZ-W resulted in the lowest impact toughness, which was indicated by the large unstable crack propagation.

Steel structures play a vital role in the marine industry for application in ships, platforms, wind turbines, bridges, or pipelines. This leads to challenges if parts made from higher strength steels have to be repaired underwater. Underwater wet welding is the most common underwater repair method and highly prone to hydrogen-assisted cold cracking, especially in higher strength steels. A common method to access this risk in dry welding is based on the calculation of the carbon equivalent (e.g., CE or CET) representing the behavior of the parent metal based on its composition. However, these formulas were not specifically developed for wet welding conditions, and the applicability of these formulas on the special requirements of wet weldments has not been validated. In the present study, the effectiveness of existing CE formulas for underwater wet welding was evaluated. It is demonstrated that the conventional approaches designed for conventional welding under dry atmospheric conditions are hardly applicable to underwater wet welding. Based on comprehensive experimental data, a mathematical model leading to improved hardness and CE formulas dedicated to underwater wet welding was developed. The new formulas demonstrated greater efficiency in predicting hardness and carbon equivalent within the analyzed data, when compared to the existing formulas used for welding under dry atmospheric conditions.

Fatigue design guidelines for welded joints are mainly derived from tests on joints with a thickness of approximately 10 mm. As thickness increases, fatigue strength typically declines, likely due to greater stress concentration or changes in stress distribution. Consequently, these guidelines adjust fatigue strength downward for thicker joints. However, for thinner plates, such as those frequently used in railway cars, test data is limited, making it uncertain whether the guidelines are applicable. This study performed a 4-point bending fatigue test on a 3 mm thick fillet-welded joint to evaluate fatigue strength. Contrary to expectations, reducing the thickness from 9 to 3 mm resulted in a decrease in fatigue strength. Nevertheless, the test results indicated a higher fatigue strength than the recommended value, supporting the applicability of the guidelines to joints with a 3 mm thickness. The study also examined the factors contributing to reduced fatigue strength in thin plates, focusing on the relationship between the number of cycles to crack initiation, local stress range, and crack growth analysis using Paris' law. It was observed that as the thickness decreases, the stress concentration at the weld toe reduces, and the number of cycles to crack initiation increases. However, the decrease in ligament length leads to a shorter crack propagation life.

Friction stir welding is a solid-state joining process that operates below the material’s melting point commonly used to join aluminum parts, avoiding the drawbacks of fusion-based methods. These resulting advantages have accelerated growth and are increasing the number of applications across a range of industrial sectors, many of which are safety–critical. Along with the increase in applications and rise in productivity the need for reliable and cost-effective, non-destructive inline quality monitoring is rapidly growing. This publication is based on the research group’s ongoing efforts to develop a capable generalized inline-monitoring solution. To detect and classify FSW defects, convolutional neural networks (CNNs) based on the DenseNet architecture are used to evaluate recorded process data. The CNNs are modified to include weld and workpiece-specific metadata in the classification. These networks are then trained to classify transient weld data over a wide range of welding parameters, three different Al alloys, and two sheet thicknesses. The hyperparameters are incrementally tuned to increase weld defect detection. The defect detection threshold is tuned to prevent false negative classifications by adjusting the cost function to fit the needs of a force-based detection system. Classification accuracies > 99% are achieved with multiple neural network configurations. System validation is provided utilizing a newly recorded weld dataset from a different welding machine with previously used parameter/workpiece combinations as well as parameter combinations and alloys as well as sheet thicknesses outside the training parameter range. The generalization capabilities are demonstrated by the detection of > 99.9% of weld defects in the validation data.

This study investigates the influence of surface integrity and the localized fatigue phenomena on the initiation and propagation of short fatigue cracks in high-frequency mechanical impact (HFMI)-treated welded joints. The treated surface region, characterized by a compressive residual stress field, smooth notch geometry, and work hardening layer, improves welded joints’ fatigue strength. However, how these surface conditions influence the fatigue damage process zone during short crack initiation and growth is not yet well known. Therefore, this study systematically investigates the influence of different surface characteristics on fatigue life modeling of HFMI-treated welded joints made of high-strength steel. This is achieved using a non-local continuum damage mechanics-based approach of crack growth and elastic–plastic finite element simulation, explicitly modeling treated surface conditions. The simulated fatigue life is first verified with experiments and then applied to various surface conditions. The simulation results show that most of the fatigue life is spent until a crack size of 0.2 mm. The compressive residual stress field greatly extends both short crack initiation and propagation life, with its degree of contribution highly dependent on loading history and residual stress change. The role of the work hardening layer is mainly concentrated on improving fatigue life during short crack initiation and the very beginning of short crack growth.

The weld diameter is the most important quality criterion in resistant spot welding and is unsually determined after destructive testing. Several standardized destructive testing methods are available for this purpose. The determination of the spot weld diameter is influenced by numerous factors. These include the measurement conditions, such as the lighting conditions, the measurement equipment used, and the person performing the measurements. The human aspect is influenced by experience and is therefore subjective. To manually evaluate a resistance spot weld, the weld diameter can be measured according to ISO 17677-1, AWS D8.1M, or DVS 2916-1, among others. The challenge here is that the statistical variation in the destructive evaluation of the spot weld diameter due to human experience is still insufficiently researched. In addition, the results of destructive testing are not statistically validated or are questioned in many scientific publications. The suitability of the destructive test methods used is often not justified or compared with other test methods. The purpose of this contribution is to statistically evaluate the human experience on manual weld diameter measurements and give recommendations, that should be taken into account in the future of some kind of issues. For this purpose, more than 180 spot welds were destroyed by torsion testing and the weld diameters were measured by 20 different participants with different levels of experience. The results show that the measurements are influenced by a number of factors, including the level of experience of the participants, the size of the weld diameters measured, the failure mode, and the duration of the measurements on a sample.

Post weld heat treatment (PWHT) is frequently employed to relieve residual stress, which affects the service performance of linear friction–welded Ti17. In this work, a Norton-Bailey creep model was introduced into the finite element analysis to investigate the mechanism of residual stress relief in linear friction–welded Ti17 during PWHT. The results show that the Norton-Bailey model can accurately predict the residual stress after PWHT, as verified by experiments. The primary mechanism of residual stress relief is stress reduction induced by the development of creep strain. Most of the residual stress relief occurs during the heating stage and the initial holding stage due to the sufficient development of creep strain. The increase in PWHT temperature is beneficial for residual stress relief. However, as the PWHT temperature exceeds ~ 630 °C, the improvement of residual stress relief is no longer significant. The relationship regarding PWHT temperature and residual stress relief is developed, which can be applied to the rapid prediction of residual stress in linear friction–welded Ti17 after PWHT.

This study investigates the friction stir butt of 2024 aluminum alloy with 6061-T6 aluminum alloy using both double rotating shoulder friction stir welding (double rotating shoulder friction stir welding, DRS-FSW) and conventional friction stir welding (FSW) techniques. The differences in joint structure and morphology and mechanical properties between DRS-FSW and FSW joints were investigated. Defect-free joints were obtained for both DRS-FSW and FSW at a rotational speed of 600 r/min and a welding speed of 30 mm/min. Compared to the cross-section morphology of the dissimilar aluminum alloy joints of FSW, the morphology of the shoulder-affected zone (SAZ) and weld nugget zone (WNZ) of the DRS-FSW joints is more complex. The longitudinal morphology of the DRS-FSW joints shows complex material flow variations. The microstructure of the weld nugget zone (WNZ) of DRS-FSW joints is dominated by recrystallization. The microhardness magnitude and distribution are approximately the same for both. The FSW tensile properties are higher than those of DRS-FSW. Both DRS-FSW and FSW tensile fracture locations are in the heat-affected zone (HAZ) on the retreating side (RS) of the joint, and both exhibit ductile behavior. This paper is a further exploratory study of the double stirring technique.

The weldability of stainless steels is largely controlled by the chemical composition, and alloys with ferritic or ferritic-austenitic solidification show the highest resistance to hot cracking. As the resulting phase balance also affects the final properties, it may be beneficial to both foresee and measure the weld metal ferrite content. The WRC ‘92 constitution diagram is currently the most accurate prediction tool available, but it does not take the cooling rate into consideration and the precision may be less accurate for stainless steels with high ferrite numbers (FNs). This study aims to assess the reliability of the WRC ‘92 diagram for weld metals with FN > 50. The chemical composition was altered through gas tungsten arc welding (GTAW) of UNS S32205 with ER347 filler wire that had been coated using physical vapor deposition (PVD) with either niobium (Nb), copper (Cu), nickel (Ni), manganese (Mn), carbon (C), or silicon (Si). The actual ferrite content was evaluated using image analysis, FeriteScope and X-ray diffraction (XRD). While predictions from the WRC ‘92 diagram were deemed acceptable for Ni, Si, and Mn, notable deviations were observed for Nb, Cu, and C. The FeriteScope exhibited a consistent trend with image analysis, albeit with slightly higher FN values, wider scatter, and the conversion factor from FN to vol% is open for discussion. The lowest accuracy and largest spread were obtained using non-contact XRD, rendering it unsuitable for ferrite measurements of welds. These findings underscore the need for improved prediction tools and appropriate measurement methods for assessing ferrite content in duplex weld metals.