Issue 48

R. Baptista et alii, Frattura ed Integrità Strutturale, 48 (2019) 257-268; DOI: 10.3221/IGF-ESIS.48.27

50 o

0,5

8

(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 k Q 

2

1

1





5

 

4300 4.3 10 T 







t

F

(1)

8/5

0

2

2





T

T

500

800

t

0

0

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].

t 8/5 (s)

Current (A)

Voltage (V)

Wire feed (m/min)

Travel speed (cm/min)

Heat input (kJ/mm)

Pass

root face

5

253 270

25.8 28.6

11.7 12.7

55.7 46.3

0.7 1.0

10

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

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