To examine the generation characteristics of excessive distortions involved with the welding-induced buckling of a thin steel plate, the temperature profiles and distortion behaviors of welded plates ...during tungsten inert gas (TIG) welding were experimentally measured. Large-deformation thermal elastic–plastic analysis based on arc physics-based heat source modeling was utilized to accurately simulate the thermomechanical behavior of the plate during welding. The calculated and measured temperature profiles and distortion behaviors were compared to validate the developed numerical analysis technique. On the basis of the developed analysis technique, the effect of geometric imperfections on the thermomechanical behavior of welded thin steel plates was further investigated. Both angular and longitudinal bending distortions were found to monotonically increase with increasing heat input because of excessive longitudinal bending distortion and the secondary generation of angular distortion during the cooling process when buckling occurred. The through-thickness gradient of the plastic strain that developed with the transient distortion behavior during welding resulted in excessive angular distortion in the welded thin steel plate. It was concluded that the transient distortion behavior during welding should be taken into consideration to accurately predict and control large welding-induced distortions in thin steel plates.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In this study, the effect of welding process and heat input conditions on the angular distortion induced by bead-on-plate welding was investigated through a numerical approach. Numerical models of ...gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW), which were developed in a previous study, were utilized for accurate distortion analyses. The calculated relation between welding conditions and angular distortion was quantified by using the conventional heat input parameter derived from welding thermal conduction theory. The results clarified the limits of applying the heat input parameter to quantify angular distortion under the various welding process and heat input conditions. In addition, the effect of the weld reinforcement generated in GMAW on angular distortion was coordinately examined by using a parameter, defined as the ratio of the area of weld reinforcement to the square of plate thickness. The effect was generally negligible except for in the case of a thin plate. Then, a parameter of the mechanical melting region on the plate thickness section was applied to quantify the angular distortion induced by GMAW and GTAW. As the results, a unified evaluation of the effect of welding process and heat input conditions on angular distortion was successfully achieved. Thus, it can be concluded that the developed parameter of the mechanical melting region on the plate thickness is the dominant factor for accurately quantifying angular distortion.
This paper presents a method to improve accuracy of measuring through–thickness residual stress for welds through deep hole drilling (DHD) technique. The focus of this study is the effect of ...dimensions of the hollow cylinder, which is manufactured by drilling and trepanning processes, on residual stress measurement at the welds. First, stress concentration–induced plastic region around a reference (drilled) hole was theoretically quantified according to value of existing stress. The plastic region around the hole is not negligible for the welds at where high tensile residual stress exists. In order to reduce the influence of the plastic region, it is considered effective to set a large ratio of trepanning diameter to drilling diameter. Another noteworthy thing is that weld residual stress is present in a relatively narrow region along a weld line. Then, DHD technique was applied to measure through–thickness residual stress at the welds of melt–run welded–plate specimens under conditions of various drilling and trepanning diameters. These DHD residual stress measurement results were compared with those measured by X–ray diffraction and contour methods and calculated by weld thermal elastic–plastic analysis. As the results, it was shown that through–thickness residual stresses measured by DHD technique were obviously influenced by dimensions of the hollow cylinder. Measurement accuracy becomes higher with increasing the ratio of trepanning diameter to drilling diameter. Meanwhile, trepanning diameter should not be larger than width of generation area of high tensile residual stress to be measured at the welds. It was concluded that a method for determining appropriate dimensions of the hollow cylinder to be drilled and trepanned was successfully proposed to accurately assess through–thickness residual stress at the welds through DHD technique.
The hot cracking susceptibility in the Trans-Varestraint test was evaluated using the nominal strain calculated using the curvature radius of a bending block and the thickness of a specimen based on ...the theory of material mechanics. The nominal strain was calculated using the material properties at room temperature. Thus, in the Trans-Varestraint test, the non-uniformity of the strain around the weld part due to the temperature distribution is not considered. Therefore, the strain in the Trans-Varestraint test cannot be evaluated correctly. The aim of this study is to reveal the loaded strain at the weld metal to understand the evaluation of hot cracking susceptibility in the Trans-Varestraint test. The loaded strain around the trailing edge of the weld pool of pure iron was measured in-situ using a high-speed camera and high-resolution optical lens. The results of strains measured using image analysis and the finite-element method at the center of the weld bead were compared. Accordingly, it was clarified that the strain was concentrated on the weld part owing to the bending occurring along the weld line, and the strain exceeding the nominal strain was loaded to the trailing edge of the weld pool.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The thermal shrinkage technique, which uses shrinkage strain to determine weld distortion, shows promise as a simple simulation for predicting the weld distortion of large welded structures. To date, ...there has not been adequate research on how to set input data based on welding conditions. In this work, we perform a parametric study using thermal shrinkage technique in which we vary the input data to investigate the optimum setting method. To compare angular distortion obtained by the thermal shrinkage technique, Metal active gas welding was conducted under five welding conditions and thermal elastic-plastic analysis was conducted under the same welding condition. Under all five conditions, the angular distortion obtained by the thermal shrinkage technique accurately reproduced that obtained by experiments and by thermal elastic-plastic analysis. We found that the optimum input data settings were the shrinkage strain of −0.012 and a shrinkage zone in which the maximum temperature reached 500°C or more. From the results, the similarity and the difference between the characteristics of angular distortion in the thermal shrinkage technique and that in the thermal elastic-plastic analysis was discussed based on the inherent strain and the moment. Moreover, the way in which inherent strain based on the both-ends-fixed-bar analogy occurred can explain the agreement in angular distortion in the case of the optimum input data settings. Our results demonstrate that a suitable setting method of input data has been established.
This study presents a computational framework for an efficient distortion analysis based on coupled process-mechanics modeling of metal active gas (MAG) welding. For coupled process-mechanics ...analysis, an integrated simulation model between bead formation, thermal conduction, and thermo-mechanical behaviors during MAG welding was developed. A combined bead formation and thermal conduction model provided bead surface and temperature profiles during welding from welding process conditions. Then, heat source parameters estimated based on welding process conditions enabled a predictive simulation of MAG welding process. The bead surface and temperature profiles obtained were used for a large deformation thermal elastic–plastic analysis of weld angular distortion. The calculations were compared with the measurements, which were obtained in a previous study, under the same welding process conditions to validate the developed analysis model. From the comparison results, we concluded that the developed model has great potential to be efficient distortion analysis that estimate weld angular distortion from welding process conditions with a high degree of accuracy. Additionally, the effect of welding process conditions on weld bead morphology, temperature profiles, and angular distortion were discussed through the developed analysis model to obtain a more detailed understanding of dominant factor influencing the weld angular distortion of MAG welded structural steel plates.
The thermal shrinkage technique with previously proposed input parameter values for single-pass welding was applied to a multi-layer butt-welded joint with four layers and six welding passes to ...validate whether these input parameters are applicable to multi-layer welded joints. The out-of-plate displacement distributions of the multi-layer welded joint obtained using the thermal shrinkage technique were in good agreement with those obtained in a thermal elastic-plastic analysis and an experiment. The angular distortion and transverse shrinkage at the center of the welding line obtained using the thermal shrinkage technique well agreed with the experimental and thermal elastic-plastic analysis results for each welding pass. Furthermore, the calculation time for the thermal shrinkage technique was 1/6 of that for the thermal elastic-plastic analysis. Our results demonstrate that the thermal shrinkage technique with the previously proposed input parameter values could be applicable to multi-layer welded joints.
In this study, welding with a trailing heat sink was applied to austenitic stainless steel for reducing the weld residual stress and distortion. The effects on temperature profiles, residual stress ...and distortion were experimentally investigated through the use of gas tungsten arc welding with and without a water-cooling device. As the results, the weld residual stress and distortion can be reduced without affecting the weld penetration by welding with a trailing heat sink. Numerical investigation was also performed using the three-dimensional thermal elastic-plastic finite element analysis. A numerical model of gas tungsten arc welding was constructed based on the physics of the welding arc. The calculated weld penetration, temperature profiles, residual stress and distortion were in good agreement with those measured under the same welding conditions. Using the simplified model of homogeneously distributed heat sink on the basis of the developed welding simulation, the effect of intensity of the heat sink on the weld residual stress and distortion was quantified. Furthermore, the mechanism of the reduction of weld residual stress and distortion was discussed based on the temperature distribution variation in welding with a trailing heat sink. Based on the results, the effectiveness of welding with a trailing heat sink in reducing the weld residual stress and distortion of austenitic stainless steel has been clarified.
We constructed a detailed welding phenomenon analysis model and a simplified analysis model using the thermal shrinkage technique capable of predicting welding deformation for thin plate box-shaped ...lap-welded joints assuming automotive components. In the thermal shrinkage technique, a new method for setting the thermal shrinkage parameter was proposed to improve the accuracy of predicting welding deformation for thin plate structure. The accuracy of each model was confirmed by comparison with the experimental results, and the calculation cost of each model was compared and evaluated.
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