Figure 1.
Four points fatigue bending tests. (a) Schematic assembly and dimensions; (b) real assembly with electrical follow; and (c) fractured specimen.
Table 2.
Chemical composition of Al-alloy 2024 T351.
| Elements | Si | Fe | Cu | Mn | Mg | Cr | Ti | Zn | Pb | Ni | Al |
|---|---|---|---|---|---|---|---|---|---|---|---|
| % | 0.105 | 0.159 | 3.97 | 0.449 | 1.5 | 0.05 | 0.018 | 0.109 | 0.056 | 0.02 | Rest |
Figure 2.
Servo-hydraulic machine for fatigue tests: Instron 8500.
Table 4.
Experimental loading conditions and equivalents’ initial and final crack lengths for different stress ratios.
| R-ratio | a0 (mm) | af (mm) | Pmin (KN) | Pmax (KN) | P (KN) | N (cycles) | ΔK0 (MP√m) | ΔKf (MP√m) |
|---|---|---|---|---|---|---|---|---|
| 0.1 | 3.34 | 7.875 | 0.115 | 1.149 | 1.034 | 382.000 | 5.395 | 22.696 |
| 0.2 | 3.31 | 7.14 | 0.237 | 1.184 | 0.947 | 569.700 | 4.85 | 16.88 |
| 0.3 | 3.365 | 7.365 | 0.348 | 1.16 | 0.812 | 547.000 | 4.22 | 15.90 |
| 0.5 | 2.735 | 6.28 | 1.25 | 2.50 | 1.25 | 240.000 | 5.535 | 15.82 |
Figure 3.
Experimental fatigue life of V-notch in four-point bending specimens’ tests of 2024 T351 Al-alloy.
Table 5.
The values of the constants of the adjustment curves.
| R-ratio | A | B | C | D | E | F |
|---|---|---|---|---|---|---|
| 0.1 | −44,955 · 104 | 282,743 · 103 | −71,01 · 103 | 8932.6 | −566.95 | 15.047 |
| 0.2 | −16,180 · 104 | 139,644 · 103 | −42.59 · 103 | 6101.5 | −424.49 | 12.113 |
| 0.3 | −10,975 · 104 | 603,626 · 103 | −132.9 · 103 | 14.714 | −823.39 | 19.20 |
| 0.5 | −56,762 · 104 | 384,000 · 103 | −104.6 · 103 | 14.404 | −1008.9 | 29.449 |
Figure 4.
Comparison of predicted and experimental fatigue life at R = 0.1.
Figure 5.
Comparison of predicted and experimental fatigue life at R = 0.2.
Figure 6.
Comparison of predicted and experimental fatigue life at R = 0.3.
Figure 7.
Comparison of predicted and experimental fatigue life at R = 0.5.
Figure 8.
Comparison of predicted and experimental crack growth rate at R = 0.1.
Figure 9.
Comparison of predicted and experimental crack growth rate at R = 0.2.
Figure 10.
Comparison of predicted and experimental crack growth rate at R = 0.3.
Figure 11.
Comparison of predicted and experimental crack growth rate at R = 0.5.
Table 6.
Coefficient of Paris model.
| R-ratio | C | m |
|---|---|---|
| 0.1 | 1 · 10−8 | 3.645 |
| 0.2 | 1 · 10−8 | 3.7053 |
| 0.3 | 9 · 10−9 | 3.8712 |
| 0.5 | 5 · 10−8 | 2.9287 |
Table 7.
Performance of Gamma model
| R-ratio | 0.1 | 0.2 | 0.3 | 0.5 | Mean value |
|---|---|---|---|---|---|
| %Dev | 4.520 | 3.892 | 1.220 | 5.200 | 3.708 |
| Prediction ratio | 0.961 | 0.968 | 0.988 | 0.951 | 0.967 |
Figure 12.
Error band scatter of predicted life at R = 0.1.
Figure 13.
Error band scatter of predicted life for at R = 0.2.
Figure 14.
Error band scatter of predicted life at R = 0.3.
Figure 15.
Error band scatter of predicted life at R = 0.5.