| Aluminum alloy welding structures have been widely applied in many fields due to the lightweight requirements. Due to its large thermal expansion coefficient, high thermal conductivity, low elastic modulus and weak high temperature yield strength, the welding deformation of aluminum alloy structure is large, especially the aluminum alloy sheet structure’s deformation. And at the same time there also exist residual stress in the welded structure. The existence of deformation and residual stress greatly reduces the assembly precision and service life of the aluminum alloy structure. So find out the forming mechanism of welding deformation and residual stress, then accurately predicting and reducing them has important significance. In recent years, with the rapid development of computer hardware technology and improving of finite element theory about welding, numerical simulation technology has been widely used to predict the welding deformation and residual stress.However, it is difficult to use the simulated results to guide the actual manufacturing of welded structures directly because of the low computational efficiency and low accuracy of numerical simulation of welding distortion. This situation restricts the more widely application of numerical simulation technology in welding engineering. Therefore, improving the computational efficiency and accuracy of numerical simulation of welding is a key problem to be solved urgently at present.The complex thermodynamic behavior during welding process is a strong nonlinear problem. The calculation of welding simulation is difficult to converge and has a low computational efficiency due to the strong singularity of stiffness matrix equation and the use of 3D model. In order to solve this problem, a thermal elastic plastic finite element model based on ABAQUS software was developed to analysis welding distortion in an aluminum alloy joint, and the influence of convergence criteria on the analytical results was discussed. The simulated results show that the convergence criteria have influence on both the calculation accuracy and the computing time to some extent. Through choosing reasonable convergence criteria, it is possible to obtain a result with sufficient accuracy and to shorten computing time.On the basis of the above research, aiming at the situation that the simulated results can’t be used to guide the actual manufacturing of welded structure directly, a new material model was put forward to describe the softening phenomenon of aluminum alloy. Meanwhile,a thermo-elastic-plastic finite element method(T-E-P FEM) considering softening phenomena of aluminum alloy welding joint, material non-linearity, geometrical non-linearity and moving heat source was also developed to predict residual stress and welding distortion high precisely. The welding temperature fields, residual stress distribution and deformation in a welding process were simulated. Meanwhile, the welding deformation were measured by experiment. The welding deformation simulated by the T-E-P FEM considering softening phenomena agrees better with the measured data, this verified the validity of the developed T-E-P FEM and the proposed material model. The simulated results show that the softening phenomenon has a great influence on welding residual stress distribution of aluminum alloy joint. And the effect on the computational result of longitudinal stress is larger than the one of transverse stress. Especially in the area of weld and heat affected zone, the distributions of longitudinal residual stress and transverse stress are greatly different between the case considering softening phenomenon and the case not considering. The simulated results of longitudinal shrinkage, transverse shrinkage and angular distortion are all decreased when considering the softening phenomenon in the process of calculation, but on the whole, the decreases are not obvious. In other words, the softening phenomenon has a weakly effect on simulated results of deformation of aluminum alloy structure. |
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