最新刊期
卷 54 ， 期 8 ， 2024
- 摘要：Accurate prediction on the welding distortion of large and complex structure manufacture is always hard in the welding engineering. Digital twin (DT) technology which is characterized by a digital-virtual model, interaction through virtual reality information, perception of hidden knowledge behind real data, and accurate prediction, possess the ability to deal with welding engineering problem in high dimension along with the numerical simulation method. Therefore, DT could be used to control the welding distortion of the big scaled and complex welding structure. In this study, a shielding structure on the top of the nuclear power plant was investigated by developing technical route based on the DT technology. The welding distortion with its distribution mechanism were studied by conducting welding manufacturing experiment and simulation which used to match the DT characteristics, to precisely predict the welding distortion of the shielding structure on the top of the nuclear power plant, and support the experimental and theoretical basement for optimizing structure design and controlling distortion. The study shows the result that the welding distortion of the shielding structure on the top of the nuclear power plant is in mm grade of agreement with that obtained by DT technology. It is also demonstrated that using DT technology could obviously decrease the uncertainty of numerical simulation in predicting the welding distortion of large scale structure and improve the precision of prediction.关键词：digital twins;large scale nuclear structure;numerical simulation;welding distortion
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发布时间：2024-08-27 - 摘要：As an advanced welding technology, laser welding technology has been widely used in high-end manufacturing industries, while the complex thermodynamic behaviors of the keyhole and the molten pool determines the quality of the joint, which has influences on the further development and the applications of laser welding technology. Numerical simulation methods have been widely used in basic theoretical research of welding such as multi-physical filed behaviors of welding process because of its their low cost and high efficiency. At present, numerical simulation methods with different scales had been developed in the multi-physics field research of laser welding. Based on the research achievements at home and abroad, the main methods and research contents used in the numerical simulation of laser welding at the atomic scale, micro-scale, macro-scale, and multi-scale coupling were summarized in this paper, and their characteristics were analyzed. Finally, the prospect of the development of multi-scale numerical simulation of laser welding was discussed.关键词：laser welding;multi-scale;keyhole;molten pool;numerical simulation
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发布时间：2024-08-27 - 摘要：The constitutive equation is a crucial component of the fully coupled thermal-mechanical-flow simulation model for the friction stir welding (FSW) process. This paper conducts a fully coupled thermal-mechanical-flow simulation analysis of the FSW process for 6mm thick aluminum alloy 6061-T6 plates. To analyze the impact of the form of the constitutive equation on the simulation results, the Chen-Liu constitutive model, the Sellars-Tegart model, and the Johnson-Cook model were used in the simulation, and their results were compared. The simulation results show that the FSW temperature field and flow field calculated by the Chen-Liu model aligned more closely with experimental results than those calculated by the Sellars-Tegart model and the Johnson-Cook model. The reason was that under the temperature conditions near the tool-workpiece interface, the Sellars-Tegart model and the Johnson-Cook model predicted higher flow stresses, making material flow difficult. As a result, the interface state between the tool and the workpiece was primarily sliding friction. In contrast, the Chen-Liu model accurately reflected the rapid softening of the material as the temperature increases. Under the temperature conditions near the tool-workpiece interface, the shear flow stress of the material was lower than the friction stress at the tool/workpiece interface. Consequently, the workpiece undergoes plastic flow due to friction, reducing the sliding friction speed between the tool and the workpiece. This reduction in sliding friction heat generation was greater than the additional heat generated by the plastic flow of the workpiece, resulting in a lower predicted welding temperature using the Chen-Liu model. Overall, the influence of the material constitutive model on the FSW process's temperature field and material flow velocity field is due to the fully coupled thermal-mechanical-flow effects of FSW.关键词：friction stir welding;numerical simulation;Constitutive Models;temperature field;material flow
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发布时间：2024-08-27 - 摘要：Making the pin largely plunge into the lower plate is a common process of friction stir lap welding (FSLW) technology, but the induced hook with an up-bending morphology reduces the effective sheet thickness of the joint, which is not conducive to obtaining the joint with high bearing capacity. In this paper, in order to realize the down-bending morphology of hook, the X-shaped reverse-threaded pin was self-designed. By this pin, the material flow behavior was simulated numerically during FSLW, and the relationship between material flow and joint formation was studied. The results showed that under the driving action of pin, the materials in stir zone (SZ) top and SZ bottom respectively flowed downwards and upwards and then accumulated in the middle of SZ, and these accumulated materials had a flowing trend along the horizontal direction. When the material accumulated zone was located above the original lap interface, the hook bent downward and the SZ width was enlarged. At the rotating velocity of 800 rpm and the welding speed of 300 mm/min, the 2024-T4 aluminum alloys FSLW joint had a 299.6 MPa tensile strength, and this value was greatly higher than the reported tensile strengths of 2000 series aluminum alloys FSLW joint.关键词：friction stir lap welding;X-shaped reverse-threaded pin;numerical simulation;material flow;formation
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发布时间：2024-08-27 - 摘要：To investigate the effect of process parameters on the atomic diffusion behavior at the Fe/W interface, a low index crystal plane Fe(100)/W(100) interface structure model was established. Molecular dynamics (MD) method was used to simulate atomic diffusion at the Fe/W interface at 1 123~1 323 K, and the specific diffusion situation was observed and the diffusion coefficient was calculated.Resultsindicate that there is a significant asymmetric diffusion phenomenon at the Fe/W interface, mainly due to the diffusion of W atoms into Fe atoms, and the longer the simulation time, the more obvious this phenomenon becomes. The radial distribution function (RDF) indicates that the ordering degree on the Fe side is higher than that on the W side. According to the mean square displacement (MSD) curve fitting, the diffusion coefficient and diffusion activation energy were obtained. At temperatures of 1 123~1 323 K, the diffusion activation energies of Fe and W at the Fe/W interface were 1.326 and 0.841 56 eV, respectively. The absolute value of the diffusion potential energy of W atom in Fe crystal is lower, making it easier to break through the energy barrier. The increasing of diffusion temperature and pressure can effectively increase the thickness of the interface diffusion layer. Increasing roughness of the interface to some extent is beneficial for increasing the thickness of the diffusion layer, but it also affects the interface closure. The basic data of diffusion coefficient can provide a theoretical basis for the microstructure control of diffusion bonding interface between low activation steel and tungsten facing the first wall material in actual industrial production.关键词：Fe/W;atomic diffusion;molecular dynamics;diffuse activation energy;thickness of diffusion layer
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发布时间：2024-08-27 - 摘要：Coaxial one-side resistance spot welding (COS-RSW) is an advanced method of joining metal and carbon fibre reinforced plastic (CFRP). In the present research, the author-developed finite element code JWRIAN-RSW was employed to model the electrical-thermal-mechanical coupled phenomena of COS-RSW between Al5052 and CFRP. The welding thermal cycle was predicted numerically and verified by experimental measurement. Cross-tension test was used to evaluate the mechanical performance of joints, the influence of welding parameters on joining strength, fracture behaviours and interface morphology was clarified. The generation of molten zone dimension was also discussed. The results showed that the predicted thermal cycle presented a good agreement with measurement, which indicated the effectiveness of numerical model. The COS-RSW joints presented two fracture modes. Low welding current resulted in a weak joining, interfacial failing and brittle fracture. The large current led to a strong bonding and ductile fracture, the failure occurred within the resin matrix. Besides, the molten zone of COS-RSW can grow up even in the early stages of cooling. Therefore, it was necessary to consider the cooling stage in the numerical model of COS-RSW to predict the molten zone dimension via peak temperature distribution.关键词：CFRP;coaxial one-side resistance spot welding;numerical analysis;temperature field;welding parameters
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发布时间：2024-08-27 - 摘要：In the multi-layer and multi pass welding of marine Ti80 titanium alloy thick plates, the material has undergone multiple thermal-stress cycles. The welding joint needs to consider the thermoplastic deformation behavior of the material under cyclic loading, and different plastic constitutive models express quite differences in material mechanical properties. Therefore, the material plastic model has a direct impact on the simulation calculation of welding residual stress. This article obtains the material parameters of the ideal elastic-plastic model, isotropic hardening model, dynamic hardening model, and mixed hardening model of Ti80 titanium alloy material through tensile tests at different temperatures (20 ℃~900 ℃) and low cycle fatigue tests at different temperatures (20 ℃~800 ℃). Simulate and calculate the welding residual stress of Ti80 welded joints using different hardening models, and measure the residual stress using X-ray. Compare the obtained residual stress results and analyze the influence of different hardening models on welding residual stress. It can be concluded that the ideal plasticity model underestimates the magnitude of residual stress, while the isotropic hardening model slightly overestimates the magnitude of residual stress in the molten pool and its vicinity. The residual stress calculation values of the dynamic hardening model and the mixed hardening model are relatively close, with the former slightly smaller and the latter more accurately predicting residual stress. From the perspective of engineering applications, it is recommended to use an isotropic strain hardening model, which has the highest value in residual stress prediction. Using this model can obtain relatively conservative prediction values.关键词：hardening model;Ti80 titanium alloy;welding residual stress;welding technology;finite element calculation
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发布时间：2024-08-27 - 摘要：The service safety and service life of welded structures have always been concerned. The Master S-N curve established on the basis of fracture mechanics is suitable for the anti-fatigue design of steel welded structures with different types of joints. In this paper, the fatigue properties of orthotropic bridge decks, T-joints, plate and tube-plate welded structures are evaluated based on the mesh-insensitive structural stress method. In the process of fatigue assessment, the effects of welding deformation, weld size and residual stress on complex welding structures are quantitatively analyzed, and the fatigue data are modified with angular deformation and average stress as correction coefficients respectively. The results show that the fatigue data of orthotropic bridge deck, T-joint considering angular deformation, plate and tube-plate structure considering the effect of residual stress are all within a 95% confidence interval of Master S-N curve. It is proved that Master S-N curve is the preferred curve for anti-fatigue design of welded structures.关键词：welded steel structure;fatigue assessment;master S-N curve;repair-welded;residual stress
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发布时间：2024-08-27 - 摘要：Geometry character of deposition layers for thin-walled parts in GMA-based additive manufacturing is researched using GMA as the heat source and H08Mn2Si wire as the additive material. Layer geometries are measured by an optical microscope. Geometry characters of deposition layers are analyzed, and its forming mechanism is also illustrated. The results show that the layer geometries in the previous four layers are unstable and have a larger fluctuation. With the increase of the number of deposition layers, the layer height decreases and then reaches a stable value. With the increase of the number of deposition layers, the layer width firstly decreases and then gradually increased to a stable value, and the layer width has a minimum value in the second layer. A series of experiments are carried out for collecting the input-output data by applying a central composite rotatable design. Nonlinear relations between deposition current, travel speed, arc voltage and layer geometry are developed based on neural network algorithms. Testing data show that the neural network model has a great prediction capability, and maximum relative errors between predicted and measured values are no more than 6.98%. According to the model, closed and open path thin-walled parts are fabricated, demonstrating the effectiveness of the model employed in the adaptive slicing process for thin-walled components.关键词：additive manufacturing;GMA;thin-walled parts;geometry character
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发布时间：2024-08-27 - 摘要：The evaluation of hot cracking susceptibility in the welding of materials is important in the manufacture. In previous studies, the applicability of the hot tearing criteria has always been a hot issue because it did not consider the grain boundary effect. In this paper, taking Al-Cu alloy as an example, the dendrite morphology and solidified path were obtained by a quantitative phase field model of polycrystalline solidification. Based on the solidified path, the applicability of the widely-used hot tearing criteria was studied, including the RDG criterion, Clyne-Davies criterion, and Sindo Kou criterion. It is found that the RDG criterion is consistent with the actual welding hot cracking tendency, and the crack generation is mainly dominated by the pressure drop between dendrites in isolated grain boundary segments. The Clyne-Davies criterion and Sindo Kou criterion result in distortion because some isolated grain boundary intervals are ignored in the calculation process. Through the research of three criteria, a reference is provided for the evaluation of the hot cracking susceptibilities of materials.关键词：hot cracking susceptibility;solidification path;phase field model;grain boundary effect
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发布时间：2024-08-27 - 摘要：A finite element model of resistance ramp butt welding process of 5052 aluminum alloy with thickness of 4 mm was established by Abaqus, and the process test was designed under the same parameters. The relationship between the formation process of the welding nugget and the electric field and temperature field during the welding process under different welding process parameters was analyzed. The accuracy of the model was verified by comparing the metallographic samples with the results of the finite element model calculations. The results show that the welding nugget of resistance slant butt welding is an ellipsoidal shape that grows along the contact surface, and the thickness of the workpiece plays a certain guiding role in the growth direction of the nugget. At the same time, due to the different material properties of aluminum alloy and welding structure, a current concentration area was formed at the center of the lower electrode in the early stage of welding. The role mechanism of the minimum voltage drop principle in slant butt welding is also discussed, providing basic scientific data for further study of the resistance eccentric spot welding process.关键词：CFRP;coaxial one-side resistance spot welding;numerical analysis;temperature field
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发布时间：2024-08-27 - 摘要：In this study, the crack propagation behavior of internal defects in aluminum alloy double-sided welded butt joints under fatigue load was analyzed based on the joint simulation method of ABAQUS and FRANC3D. The accuracy of the symmetric model was verified by comparing with the stress intensity factor K and fatigue life N at the crack tip under different crack depth a in the full model of the welded joints. Based on the symmetric model, the fatigue propagation law of initial defects under different shape ratios (depth a / length 2c) was analyzed. The results show that when the depth a of the elliptical defect is constant, the initial stress intensity gradually increases with the increasement of the defect length 2c, and the fatigue life of the specimen is significantly reduced. When the length of the long axis is increased by 3 times, the fatigue life is reduced by 50%. As the crack propagates, the ratio of a/c gradually approaches 1, that is, the shape is close to a circle.关键词：internal defects;simulation;shape ratios;crack propagation;fatigue life
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发布时间：2024-08-27 - 摘要：Aiming at the problem of weak performance and easy fatigue fracture of welded joints of Marine steel, three methods were used to strengthen the welded joint of marine high-strength steel, including ultrasonic impact, weld toe repair and weld toe repair + ultrasonic impact composite treatment. The residual stress, stress concentration factor and fatigue performance of the joint strengthened by different processes were compared and studied. The results show that: (1) ultrasonic impact treatment can effectively reduce the residual stress of the joint and form beneficial compressive stress on the surface, while weld toe repair can not improve the residual stress of the joint, and even slightly increase the residual stress; (2) All three treatment processes can reduce the stress concentration at the weld toe, and the weld toe repair treatment can significantly reduce the stress concentration coefficient; (3) All the three treatment processes can improve the low-cycle fatigue performance of the joint. The fatigue life of the joint is increased by 58% after ultrasonic impact treatment, by 249% after weld toe repair, and by 460% after weld toe repair combined with ultrasonic impact treatment. The compound treatment process of weld toe repair and ultrasonic impact gives consideration to the advantages of weld toe repair and ultrasonic impact treatment, which can not only significantly reduce the stress concentration of weld toe, but also obtain beneficial residual compressive stress, and can be applied to strengthening key parts of ship welded structure.关键词：ultrasonic impact;weld toe repair;residual stress;fatigue performance;weld joint
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发布时间：2024-08-27 - 摘要：The ring-stiffened cylindrical shell structure has strong pressure resistance, convenient assembly and welding process, and is widely used in the industry. However, welding usually involves residual stress and deformation, which may have a certain impact on the load-bearing capacity. Using the finite element analysis method, the full process of welding and pressure bearing was simulated on the titanium alloy of ring-stiffened cylindrical shell structure. It was found that the equivalent Mises stress is close to the yield strength of the material after welding, and the total deformation was small, with a maximum of 17.23mm. For simulating actual pressure, the deformation of the structure shows an approximately linear change when the pressure is loaded from 0 to 20MPa. The structures can bear the load well. As the pressure continues to increase, the stress level increases, and the model will begin to appear nonlinear deformation trend. It was found that the presence of residual stress has no significant impact on the load-bearing capacity of the structure. Therefore, by analyzing the welding stress/deformation and carrying capacity of the structures, the technical support is provided for load-bearing level.关键词：titanium alloy;ring-stiffened cylindrical shell;welding stress and deformation;carrying capacity;FEM simulation
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发布时间：2024-08-27 - 摘要：The long-distance pipeline passes through mountains and hills, and the laying and welding process sometimes needs to be carried out at a 5°~45° slope. The pipeline in mountain areas with large slopes often fails due to excessive tensile stress, so its stress distribution becomes a necessary research topic. In this paper, the stress distribution of welded joints of X70 steel with a slope of 25° using automatic welding is studied. Based on the Thermal-Metallurgic-Mechanical theory, the finite element model of the welded joints of pipelines in mountainous areas with high slopes is established, and the actual heat source model and construction environment are taken as the boundary conditions. The welded joints are uniquely divided into higher and lower sides, and finally, the stress distribution is obtained, which fills the gap in the study of the stress distribution of welded joints in mountainous areas with large slopes. The hole-drilling method and the coercive method are used to measure the stress level of the inner and outer surfaces of the pipeline to verify the accuracy of the stress simulation. The welded joints are subjected to axial stress along the pipe due to gravity and supporting force. So the stress distribution of welded joints of pipelines in mountain areas with large slopes is different from that of pipelines without slope. The average width of the coarse-grained zone of the root welding layer of the higher side is 27 μm wider than that of the lower side. The average width of the coarse-grained zone of the hot welding layer of the higher side is 21 μm wider than that of the lower side. The tensile stress of the root welding layer of the higher side is 135 MPa higher than that of the lower side, and the high tensile stress zone of the root welding layer of the higher side is 1.6 mm wider than that of the lower side.关键词：large slopes;automatic welding;numerical simulation;higher and lower sides
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发布时间：2024-08-27 - 摘要：Since a small deviation in the off-focus value can lead to an unstable weld pool, the laser welding of thin plates is highly susceptible to this parameter. Based on numerical simulation, effects of off-focus on the dynamic behaviors of the weld pool in laser welding of 430 ferritic stainless-steel plates in 0.6mm thick were investigated. The reasons behind the formation of spatters on the back of the weld bead were examined. The results show that the position and distribution of laser heat input in the weld pool are primarily determined by the off-focus. As the off-focus value decreases, the keyhole in the weld pool gets deeper. A negative off-focus (-0.1 mm) creates a fully penetrated keyhole, while zero (0 mm) and positive (0.01 mm) off-focus creates smaller keyholes. All off-focuses form weld pools with a same waist structure, and the maximum flow velocities are observed on the surfaces of the weld pool and keyhole. Two eddy currents flowing from the middle waist to the upper and lower surfaces exist in the weld pool, and the molten metal on the upper surface of the weld pool flows forward from its rear to its front. Due to the evaporation force and high surface flow velocity, the keyhole continuously seals off in its middle, leading to closed bubbles at the bottom. Only negative off-focus causes back spatter, while zero and positive off-focus do not cause it. In the case of negative off-focus, small droplet spatters form on the back of the weld during the initial formation of the weld pool, chiefly caused by the gravity and surface flow. Jet spatters resembling large particles are formed due to bubble rupture during the final stage of the formation of the penetrated keyhole. There is a relatively stable shape and flow of the weld pool in the case of positive off-focus, and the predicted profile of the weld bead on the cross-section is in good agreement with the experimental results.关键词：laser welding;ferritic stainless-steel;off-focus;weld pool dynamic;back spatter
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发布时间：2024-08-27
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