Issue34

K.L. Yuan et alii, Frattura ed Integrità Strutturale, 34 (2015) 476-486; DOI: 10.3221/IGF-ESIS.34.53 480 The welded joints for as-weld and UIT were fabricated by one pass welding with leg length of 7mm.The used UIT equipment was Esonix TM 27 UIS. The operating frequency of ultrasonic generator was 27 kHz, shifting speed of 10 mm/s and 3-mm-diameter hardened metal pins. Welding material Wire diameter[mm] Speed [mm/min] Current [A] Voltage [V] Arc efficiency SF-1 1.2 300 250 29 80% Table 1 : Welding conditions. Simulation of welding process For welding simulation, a half symmetrical 3D model of cruciform joint is created. This FE model has been constructed for small width of 4 mm, in order to be most effective considering the accuracy and computational effort (see Fig.6). Therefore both sides of this segment are restrained in Z-direction, to simulate the specimen in plane strain state. The FE model mainly employs 8-node hexahedral solid elements except for few wedge elements in the weld bead region. Near the weld toe, an extremely fine mesh (0.2×0.1×0.2mm) is required for the following UIT process simulation. In the first step of thermal analysis, heat input (1160 J/mm) is given all at once to the weld metal and an initial temperature of 1400°C for activation of the weld bead material elements is assumed. Accompanying with heat radiation and convection, the cooling-down period between the subsequent weld is set as 1 hour. For the second step of mechanical analysis, the material model is assumed to follow von Mises yield criterion with bilinear kinematic hardening. The used temperature-dependent thermal and mechanical material properties are illustrated in Fig.7. Figure 6 : Finite element model for welding simulation. a) b) Figure 7 : Temperature-dependent material properties referring to SYSWELD material database [23].