Issue 52

W. Xiangming et alii, Frattura ed Integrità Strutturale, 52 (2020) 25-32; DOI: 10.3221/IGF-ESIS.52.03 26 and analyzed the residual stress in the fusion zone and heat affected zone. In another study, Mato Peridic et al. [11] simulated and tested the residual welding stress and defects in T joint, and proved that the peak value of residual stress appeared near the weld toe. Inoue et al. [12] studied the effect of coupling of temperature, phase transition and thermal stress in the process of temperature change accompanying phase transition, and proposed a general form of constitutive equation under the coupling condition. However, reports on the welding simulation of T joint of S355 steel are scanty. Based on the finite element numerical simulation method, the residual stress of T joint of steel S355 after wielding was calculated as a function of the thermo-mechanical coupling characteristics of multi-layer welding. Then the residual stress of T joint with tangent tube and sheet was measured with X-ray diffraction test. The transient stress changes and the distribution of residual stresses during welding were simulated. The results of the numerical simulation laid a foundation for the subsequent optimization of welding process parameters and the realization of residual stress control based on numerical simulation. E STABLISHMENT OF FINITE ELEMENT MODEL Establishment of Finite Element Mesh Model inite element meshing was accomplished with Hypermesh software. The total number of meshes was 488910, with 452741 nodes. The maximum mesh element size was 5 mm × 3 mm × 0.8 mm, while the minimum mesh element size was 5 mm × 1 mm × 0.8 mm (Fig. 1 and 2). In order to ensure the convergence of the calculation results, the base grids of the weld and immediate vicinity of the weld were divided tightly in the mesh generation process, while the mesh far from the weld was sparsely divided [10]. Figure 1: Network model. Figure 2: The finite element model of T joint. At the end of mesh partitioning, Visual-Mesh was imported for grouping, and constraints were imposed. The constraints are shown in Fig. 3, i.e., exerting clamping on the node along the axes pointed by the arrow to ensure arrest of the rigid motion. Figure 3: Constraints. Establishment of Material Model Considering the effect of phase change on residual stress and deformation during welding, the main phases of materials such as ferrite, pearlite and martensite were loaded in the simulation process. Their thermophysical properties are shown in Fig. 4. F