PSI - Issue 23

F.V. Antunes et al. / Procedia Structural Integrity 23 (2019) 571–576 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

575

5

explained by the initial yield stress. Figure 5 presents the variation of  K el with Y 0 . The increase of Y 0 increases  K el , which is logical since the limit of elastic deformation is defined by the yield stress. The reduction of  K eff (by  K el ) moves the da/dN-  K eff to the left side.

5

5

7050-T6 AA 6082-T6 AA 6016-T4 AA 304L SS

4

4

7050-T6

0.5 ]

0.5 ]

3

3

2  K el [MPa.m

2  K el [MPa.m

6082-T6

6016-T4

1

1

0

0

0

100

200

300

400

500

0

5

10

15

20

25

Y 0 [MPa]

 K [MPa.m 0.5 ]

Fig. 5. Effect of yield stress on  K elas (plane stress).

Fig. 4. Effect of load range on  Kelas (plane stress).

3.3. Elastic-plastic regime

Figure 6 shows the variation of plastic CTOD range,  p with the elastic deformation range,  e . There is a well defined relation between  p and  e , which is non-linear. However, there is a great influence of material, and a relatively influence of stress ratio (R) on this relation. Figure 7 plots the fatigue crack growth rate, da/dN, versus plastic CTOD obtained for different materials. For each material, the increase of  p increases da/dN, as is logical since FCG is expected to be linked with crack tip plastic deformation. There is a great difference between materials, which means that for the same plastic deformation at the crack tip there are different fatigue crack growth rates. These da/dN-  p relations are expected to be material properties which can be used to predict FCGR for other loading conditions. The CTOD versus load curve can also be used to predict fatigue threshold.

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

1.4

304L

18Ni300; R=0.05 18Ni300; R=0.3 18Ni300; R=0.6

304L

1.2

R² = 0.9994

R² = 0.9994

AA2024-T351

AA2024-T351

R² = 0.9887

7050-T6 AA 6082-T6 AA 2050-T8 AA 304L SS

R² = 0.9887

1

R² = 0.999

R² = 0.999

2024 - R07 2024 - R05 2024 - R03 2024 - R01 304L - R07 304L - R05 304L - R03 304L - R01

2024 - R07 2024 - R05 2024 - R03 2024 - R01 304L - R07 304L - R05 304L - R03 304L - R01

R² = 0.9957

R² = 0.9957

0.8

R² = 0.9837

R² = 0.9837

R² = 0.9959

R² = 0.9959

R² = 0.9964

0.6

R² = 0.9964

δ p [ μ m]

δ p [ μ m]

da/dN [  m/cycle]

0.4

R² = 0.9987

0.2

R² = 0.9987

0

0

0.5

1

1.5

2

0

0.5

1

1.5

2

0

0.5

1

1.5

2

 p [  m]

δ e [ μ m]

δ e [ μ m]

Fig. 6. Relation between elastic and plastic deformation.

Fig. 7. da/dN versus plastic CTOD range,  p .