Issue 46

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

The crack length was measured using a magnifying optical binocular bezel and a stroboscope mounted on a device attached to the machine.

Figure 4: Dimensions of the CT50 specimen used for cracking tests.

Propagation rates The fatigue crack propagation tests were carried out for both materials (Fig. 5), in the range of speeds between 4.10 -5 and 2.10 -2 mm/cycle at ambient air and with a load ratio (R = 0.1). The values of  K vary from: - 10 to 47 in aluminum 6082-T6 - 10 to 45 in FSW welded aluminum 6082-T6. The results obtained for the different specimens are represented by Fig. 5:

1

6082 welded 6082

0,1

0,01

1E-3

da/dN (mm/cycle)

1E-4

10

100

 K (MPa m 1/2 )

Figure 5: Evolution of the cracking speed as a function of  K for the two materials.

In order to compare more clearly and more systematically the evolution of the cracking rate in the two grades, we chose to represent them by their respective linear regression lines obtained from the experimental points (seven point method) on the linear parts of the curves. Indeed, we can notice that the curves present an almost rectilinear look on a large part of the domain explored, being able to be presented by PARIS’ law of the form:

da C K dN  

  m

(2.1)

The results of the cracking tests obtained in the two materials respectively recorded in the Tab. (3).

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