2. Theoretical research results of numerical simulation of welding mechanics

Over the years, we have been engaged in the field of numerical simulation of welding mechanics, and have carried out extensive international cooperation and achieved the following main results:

1) The finite element analysis method and corresponding computer program for welding heat transfer under various welding heat input conditions are developed, which solves the problems of “oscillation” and improves the calculation accuracy.
2) The effective methods for improving the accuracy and stability of 3D welding thermoelastic-plastic finite element calculation are studied and the corresponding computer programs are developed. It has been successfully applied in the analysis of several 3D complex welded structures and the analysis of instability deformation.
3) The analysis of dynamic and residual stress considering phase transition was successfully carried out.
4) Introducing the viscoelastic-plastic finite element method considering high temperature creep, the comprehensive evaluation of the evaluation criteria of local post-weld heat treatment is carried out, and a new evaluation method is proposed, which has received extensive attention internationally.
5) Proposed and developed a residual plastic deformation finite element method based on elastic calculation for predicting welding deformation, including the use of three-dimensional and shell-shell elements and considering large deformations, providing a powerful tool for the analysis of large complex welded structures. This technology has brought breakthroughs to practical engineering applications.
6) Successfully established mathematical models for several special welding and joining methods, such as residual stress and transition layer optimization of ceramic metal diffusion joints, resistance spot welding of galvanized steel sheets, expansion joint model, water-fire bending plate, friction stir welding The heat transfer and mechanical models have achieved good results.

3. Comparison of welding deformation and stress prediction methods and their application scope

According to the development of prediction theory of welding deformation and residual stress, the following methods can be summarized, each of which has its advantages and disadvantages and its application range:

1) Empirical curves and formulas based on experiments and statistics 2) Residual plastic deformation method based on one-dimensional analysis 3) Thermal elastic-plastic finite element analysis of welding 4) Intrinsic strain based on elastic finite element analysis 5) Considering phase transition and coupling Finite element analysis of effects 6) Viscoelastic-plastic finite element analysis considering high temperature creep

The following is a simple T-beam longitudinal bending caused by the bending deformation, comparative analytic method, three-dimensional thermoelastic finite element method, three-dimensional solid element inherent strain method and plate element inherent strain method and other four methods of prediction results, and measured The data were compared and analyzed for their advantages and disadvantages and applicable conditions. The structural dimensions of the T-beam: the cross-section of the composite plate is 180×6 mm, the cross-section of the panel is 30×6 mm, and the length is 900 mm. The material is low carbon steel. Welding parameters: one-sided welding of a fillet weld with a height of 6 mm, welding heat input qv=10.5KJ/cm, welding speed v=1cm/s. The average bending deflection of the six beams obtained was found to be f = 1.42 mm. Fig. 2 is a welding deformation diagram predicted by the inherent strain method of the plate unit. Tables 1 and 2 compare the results and characteristics predicted by the four methods.

Figure 2 T-beam welding deformation diagram

It can be seen from Table 1 and Table 2 that the results of several welding deformation predictions are close to the measured data and thus reliable. For beam-type structures with regular cross-sections, the welding deformation can be directly obtained by analytical methods. When only the welding deformation of large three-dimensional structures is predicted, the three-dimensional solid element inherent strain finite element method can be used. For the prediction of welding deformation of thin-walled complex structures, the inherent strain finite element method of the shell-and-shell element can be used. At this time, the unit mesh division can be further simplified. The 3D thermal elastoplastic analysis has a large calculation workload (this example is more than 24 hours). It records the whole process of welding thermodynamics, not only can obtain the overall residual deformation of the welded structure, but also can analyze the residual stress, and can also analyze Dynamic stress and deformation throughout the welding process. It is therefore a powerful tool when you need to understand the laws of welding deformation and stress in detail. In addition, the influence of phase change needs to be considered when analyzing high-strength steel. In the case of high temperature stress relief treatment, creep analysis must be introduced.

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