On the Relationship between Structural Quality Index and Fatigue Life Distributions in Aluminum Aerospace Castings †
Abstract
:1. Introduction
2. Materials and Methods
2.1. Experiments by Ozelton et al.
2.2. Statistical Analysis
3. Results
4. Discussion
- the original rather fine scattering of defects remaining in suspension in the original poured liquid from the crucible or ladle (prior damage). These “old” bifilms have a typical minimum thickness of approximately 10 μm and show only coarse wrinkles.
- the large new bifilms (new damage) that would have been produced during the melt transfer and/or pouring and filling if the filling system was not designed properly. These “young” oxides have a minimum thickness of tens of nanometers or less and show fine wrinkles on fracture surfaces of castings.
5. Conclusions
- The quality index, QT, can be used to characterize the structural integrity of D357 and B201 aluminum alloy castings.
- Probability plots for both QT and Nf distributions for B201 showed strong indications of Weibull mixtures.
- There is a strong relationship between the mean QT and Nf values as calculated from estimated Weibull parameters.
- There is a strong negative correlation between the proportion of QT in Region 1 and probability of survival for 105 cycles. Similarly, a strong positive correlation exists between the proportion of QT in Region 3 and probability of survival for 105 cycles, providing further evidence for the strong link between elongation and fatigue performance.
- The statement that the elongation requirement in industrial specifications is a de facto fatigue life specification is justified.
Author Contributions
Conflicts of Interest
Nomenclature
β0, β1 | alloy dependent constants |
f | Weibull probability density function |
Γ | gamma function |
m | shape parameter |
σ | mean value of the Weibull distribution |
Nf | fatigue life |
σ0 | scale parameter |
p | fraction of the lower distribution |
σT | threshold value below which no failure is expected |
P | probability of failure |
σY | yield strength (MPa) |
PL | probability from lower distribution |
eF | elongation |
PU | probability from upper distribution |
eF(max) | maximum elongation, ductility potential |
QT | quality index |
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D357-T6 | B201-T7 | |||
---|---|---|---|---|
Solidification Rate | Slow | Fast | Slow | Fast |
Pouring T (°C) | 782 | 748 | 787 | 732 |
Chill Material | Iron | Copper | Iron | Copper |
Alloy | Solidification Rate | Distribution Tag | Weibull parameters | ||||
---|---|---|---|---|---|---|---|
p | σT | σ0 | m | ||||
D357-T6 | Slow | QT | 0.077 | 0.239 | 1.52 | ||
Nf | 37,291 | 57,340 | 1.43 | ||||
Fast | QT | 0.010 | 0.433 | 2.27 | |||
Nf | 38,688 | 120,966 | 0.74 | ||||
B201-T7 | Slow | QT | Lower | 0.250 | 0 | 0.066 | 1.13 |
Upper | 0.179 | 0.234 | 1.34 | ||||
Nf | Lower | 0.114 | 26,351 | 16,963 | 1.62 | ||
Upper | 67,720 | 90,284 | 0.82 | ||||
Fast | QT | Lower | 0.188 | 0 | 0.200 | 4.79 | |
Upper | 0 | 0.623 | 6.26 | ||||
Nf | Lower | 0.281 | 51,372 | 18,730 | 0.95 | ||
Upper | 113,610 | 58,081 | 0.57 |
Distribution Tag | P (QT ≤ 0.25) | P (0.25 ≤ QT < 0.70) | P (QT ≥ 0.70) | P (Nf ≥ 105) | ||
---|---|---|---|---|---|---|
D357 | Slow | 0.458 | 0.529 | 0.014 | 0.321 | |
Fast | 0.230 | 0.713 | 0.056 | 0.546 | ||
B201 | Slow | L | 0.989 | 0.011 | 0.000 | 0.000 |
U | 0.183 | 0.763 | 0.054 | 0.650 | ||
Fast | L | 0.946 | 0.054 | 0.000 | 0.084 | |
U | 0.003 | 0.871 | 0.126 | 1.000 |
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Özdeş, H.; Tiryakioğlu, M. On the Relationship between Structural Quality Index and Fatigue Life Distributions in Aluminum Aerospace Castings. Metals 2016, 6, 81. https://doi.org/10.3390/met6040081
Özdeş H, Tiryakioğlu M. On the Relationship between Structural Quality Index and Fatigue Life Distributions in Aluminum Aerospace Castings. Metals. 2016; 6(4):81. https://doi.org/10.3390/met6040081
Chicago/Turabian StyleÖzdeş, Hüseyin, and Murat Tiryakioğlu. 2016. "On the Relationship between Structural Quality Index and Fatigue Life Distributions in Aluminum Aerospace Castings" Metals 6, no. 4: 81. https://doi.org/10.3390/met6040081