Issue 46

T. Bounini et alii, Frattura ed Integrità Strutturale, 46 (2018) 1-13; DOI: 10.3221/IGF-ESIS.46.01

Influence of Welding Speed on Heat generation From the Fig. 9, it is remarkable that decreasing the welding speed produces a hotter weld.

Heat generation during friction stir welding arises from two main sources: friction at the surface of the tool and the deformation of the material around the tool. Increasing the welding speed produces less work of deformation and in result, less heat generated. The temperature distribution shows an asymmetric profile due to the stirring effect of the pin. Influence of welding Speed on Longitudinal Residual Stress It should be observed that residual stresses in FSW processes are due both to thermal and mechanical causes. The former are due to the friction forces work and to the deformation work both decaying into heat. The latter are strictly connected to the strong gradients of strain and strain rates occurring due to the tool pin action on the material to be welded and which determine relevant microstructure changes in the parent material but low influence in the residual stresses [10].

40 mm/min 80 mm/min 100 mm/min 200 mm/min

80 mm/min 100 mm/min 200 mm/min

1,2

3,2

1,0

2,4

0,8

1,6

0,6

0,4

0,8

0,2

Longitudinal Residual Stress (MPa)

Longitudinal Residual Stress (MPa)

0,0

0,0

-8,0E-04

-4,0E-04

0,0E+00

4,0E-04

8,0E-04

8,0E-04

4,0E-04

0,0E+00

+4,0E-04

+8,0E-04

Distance from the weld center (mm)

Distance from weld center (mm)

(a) (b) Figure 10: a) longitudinal stress profiles in a cross-section of the workpiece (Rotational speed: 710 rpm). b) Only 80, 100 and 200 mm/min welding speeds are represented.

40mm/min 80mm/min 100mm/min 200mm/min

40mm/min 80mm/min 200mm/min

1,2

10

1,0

8

0,8

6

0,6

4

0,4

2

0,2

Longitudinal Residual Stress (MPa)

Longitudinal Residual Stress (MPa)

0

0,0

-8,0E-04

-4,0E-04

0,0E+00

4,0E-04

8,0E-04

-8,0E-04

-4,0E-04

0,0E+00

4,0E-04

8,0E-04

Distance from the weld center (mm)

Distance from welding center(mm)

(a) (b) Figure 11: a) Longitudinal stress profiles in a cross-section of the work piece (Rotational speed: 1400 rpm). b) only 40, 80 and 200 mm/min welding speeds are represented.

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