Issue 48

R. Baptista et alii, Frattura ed Integrità Strutturale, 48 (2019) 257-268; DOI: 10.3221/IGF-ESIS.48.27 259 (a) (b) Figure 1 : Schematic representation of (a) joint design and (b) welding sequence (A: base metal; B: face pass; C: root pass) (dimensions in mm). The applied heat input in each weld was determine using Eqn. (1) [6]. For the first pass the resulting t8/5 cooling time was 5 s while for the second pass was 10 s (Tab. 3).   2 2 2 2 5 8/5 0 2 2 0 0 1 1 4300 4.3 10 500 800 k Q t T F T T t                               (1) where T 0 represents the working temperature (in this case 23 0 C), Q the heat input (kJ/mm), k is the thermal efficiency of the welding procedure (0.8 for the MAG welding case) and t is the workpiece thickness (8 mm). Finally, F 2 and is the joint type factor in two-dimensional heat conduction (0.9 in butt welds) [6]. Pass t 8/5 (s) Current (A) Voltage (V) Wire feed (m/min) Travel speed (cm/min) Heat input (kJ/mm) root 5 253 25.8 11.7 55.7 0.7 face 10 270 28.6 12.7 46.3 1.0 t 8/5 : cooling time from 800 ºC to 500 °C. Table 3. Welding parameters used . Figure 2 : Paris Law data fit for the experimental results obtained on the heat affected zone. Experimental Paris Law determination Fatigue specimens were produced according to ASTM E466 96 [7]. Fatigue crack growth behavior was evaluated in the HAZ region at room temperature, according to ASTM E647 [8]. Fatigue tests were also carried out at room temperature with an MTS 810 servo hydraulic machine. The tests were performed under force-controlled mode using sinusoidal axial loading with constant amplitude. The stress ratio was 0.1 with Pmax = 10 kN, and Pmin = 1 kN. The load frequency was 5 50 o 8 0,5