PSI - Issue 42

P. Ferro et al. / Procedia Structural Integrity 42 (2022) 259–269 P. Ferro et al./ Structural Integrity Procedia 00 (2022) 000 – 000

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where elastic, plastic and thermal stiffness matrix are denoted by [D e ], [D p ] and [D th ], respectively, while stress, strain and temperature increment are represented by d  , d  and dT, respectively. Among the components of total strain, elastic, plastic, and thermal strains are governed by the isotropic Hooke’s law, Von Misses criterion, and temperature dependent coefficients of thermal expansion, respectively. The differential form of total strain in terms of the above three components are: (12) Finally, the kinematic strain hardening model was chosen while clamping condition was imposed as isostatic and thermo-mechanical properties as a function of temperature were taken from Special Metals® data base (www.specialmetals.com) Fig. 4 shows the mesh used in the numerical model with a detail of the elements group, B1, B2 and B3 that were progressively activated according to the simulated welding pass. It is observed that for symmetry reasons only one half of the joint was modelled using 25340 8-node brick elements. Moreover, the mesh was refined near the weld bead to correctly capture the thermal gradients induced by the heat source. d ε ij = d ε ij e + d ε ij p + d ε ij th

Fig. 4. Mesh of the numerical model with a detail of elements groups (B1, B2 and B3) used to simulate the multi-pass welding process.

3. Results and discussion Metallographic and X-ray radiography analyses of the welded joints revealed sound welds without defects and a fully penetrated bead. This allowed confirming the good welding parameters used in the experiments. The starting point of any CWM-based simulation is the calibration of the heat source parameters (Tab. 4) via experimental analysis. In this work, a cross section of the welded joint was used to compare the FZ dimensions and shape with those obtained by the numerical model. The results of the calibration are shown in Fig. 5 while the corresponding source parameters values were already reported in Table 4. The thermal calibration resulted quite good and sufficient to obtain a good residual stress-strain field prediction. Figure 5 shows the 3D shape of isotherms, as well, according to the analyzed welding pass.